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Kickstart
The Oracle



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PostPosted: 00:26 - 19 Oct 2012    Post subject: Reply with quote

tahrey wrote:

Pretty sure my airbox design IS dire Very Happy
Seen at least a couple of these with K&N's bodged on... though that might not actually make a short shit of difference.


Biggest difference is probably noise! With an air filter the important bit is surface area, but not sure how small the original filters surface area is (K&N being pleated does increase it quite a bit, but plenty of bikes have pleated standard filters).

Quote:

[quote="tahrey"]
Strange how a lot of that seems to then just get tossed out the window when people start "tuning" their engines though? And it all still appears to work? Confused


Probably does most of the time! As a rough rule of thumb anything less than 10% gain you will not feel, but what you will feel is changes in the power delivery. For example if you lose a bit of top end and a load of bottom end / mid range it will likely feel faster.

tahrey wrote:

It's starting to look that way Smile
It just seemed like the easier, lower risk option at first.


Thumbs Up

Quote:
Which is only 37mph if I'm calculating it properly? Erm. I don't know what I'm supposed to take from this. In any case, the engine can presumably handle 10500~11000rpm (as this is about where the limiter is) but I don't intend to take it much beyond 9000 should I be able to do any of this work, so hopefully it shouldn't be too much of a stress on the thing.


Mean piston speed is a good rough indicator of the limits of revs. Increasing that is quite risky.

tahrey wrote:
The liner looks to be about 2mm thick, though I haven't any calipers to put on it and check (maybe use a ruler at the top end?), and it thins almost to a point at the bottom.

So I guess I can bore it out by 1mm (or 2mm if we're measuring diameter?) and still have a reasonable amount of it left?


That seems quite a limited amount. I would expect the liner to be shaped like an upside down top hat and thicker at the top.

tahrey wrote:
So it'd need to be a solid lump of metal, maybe with a gasket each side for sealing?


Yep.

All the best

Keith
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tahrey
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PostPosted: 11:17 - 22 Oct 2012    Post subject: Reply with quote

Teflon-Mike wrote:
tahrey wrote:


Let us just recall Robert the Bruce and the spider Razz


Yes..... but he stood to gain a whole country by his perceverance.... I dont even think a lock-sporran Scot would be so tight as to think a couple of Cg cc is worth ALL THIS!


Eh, it's amusing me if nothing else!

After actually having the engine to bits, it is starting to look increasingly unlikely - maybe I'll just shove a NOS kit on it instead for the occasional tricky hill - but I'm still at least interested in the theoreticals.
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Teflon-Mike
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PostPosted: 12:34 - 22 Oct 2012    Post subject: Reply with quote

tahrey wrote:
Eh, it's amusing me if nothing else!

After actually having the engine to bits, it is starting to look increasingly unlikely - maybe I'll just shove a NOS kit on it instead for the occasional tricky hill - but I'm still at least interested in the theoreticals.


N2O...... on a CG...... for hills......... yup..... could work.......

Give it up Tahrey... just, just give it up.

Honda CD200 the 15bhp, you want with 80+mpg potential, and the extra low and mid-range stomp to do hills and shit.

Honda CB Two-Fifty.... stroked version of same in lighter more modern frame, even more of what you want

Good examples of either available for less than sorting your CG motor.

Better still CB250RS single, 31bhp 100mph potential and still 90mpg furgality, AND all three of them are often cheaper to insure than a 125 scrote magnet. probably enough to make up for the wopping extra £15 a year road tax you seem deturmined to try and avoid!

There's a certain pervesity of shedology going on here, that is well beyond 'amusement' and long into the arena of self-delusion, mate!

Kept in the cerebral, yes, its all quite interesting, but..... its a CG... it will ALWAYS be a CG, and the best thing about CG's is...... well, they are CG's!
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tahrey
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PostPosted: 13:30 - 22 Oct 2012    Post subject: Reply with quote

Kickstart wrote:

((air filter))
Biggest difference is probably noise! With an air filter the important bit is surface area, but not sure how small the original filters surface area is (K&N being pleated does increase it quite a bit, but plenty of bikes have pleated standard filters).


*holds hands in front and makes a thumb-and-finger square about the right size*

Er... roughly... 150~200 square centimetres? The paper side (it's got one side paper the other size gauze) is indeed pleated, but the metal one isn't.

It's fed by, and then feeds down into a tube that's probably more in the 10-15 cm^2 range, however, and a carb with a smaller aperture still. Exhaust valve is nice and large at least Very Happy



Quote:

Mean piston speed is a good rough indicator of the limits of revs. Increasing that is quite risky.


Ah, because it'll put more stress on the conrod joints I suppose? And 37mph is fairly quick if you're doing it within a small bore and changing direction a couple hundred times a second...

So the idea would be to try and keep the max piston speed about the same if possible? Maybe even requiring resetting the limiter "just in case" if it's stroked?


Quote:

((liner))
That seems quite a limited amount. I would expect the liner to be shaped like an upside down top hat and thicker at the top.


Good call. Once I'd cleaned the old gaskets off properly (oh good god was that a lot of work, I've never experienced anything quite so tenacious) the situation was more clear, and there's a bit more space to work with. The oilways do seem to be pretty close to the edge however, as are the guide dowels. I've measured up, got photos etc to pull actual figures from (to within the nearest millimetre, maybe half millimetre anyway, just for theoretical basis for now), and it seems like the story holds - you could put a thinner liner in the bore, if only it (and therefore the piston) would fit in the bottom end.


Aaaaaaaanyway, I have more pressing matters now, that I don't think are worth splitting to another thread.

1/ How much of a pain in the balls am I in for if there's a bolt stub stuck in one of the engine mount holes (don't ask me how, it came like that!) and nothing I have will touch it? I might get some harder drill bits (nothing I have at the moment is any better than HSS) and try it in something approaching a more professional fashion IE taking it slow and playing a hose on the drill site, but I'm not too confident. I ended up giving up on drilling out another one where the bolt had seized (managed to make a dent about 3 mm deep, if that) and just dremeled the nut into 3 pieces instead then whacked it with a hammer to break it off.

Right now the engine is in the frame (I cut the stub off flush with the engine casing) and seems relatively secure with only three bolts, but like hell am I riding it any distance like that given my usual luck. It is at least one of the front bolts so it's very easy to get at later on, just undo the mount plate and there it is...


2/ I've got everything back together so it runs with the new bottom end (with the main horrible noise being a currently loosely-attached exhaust echoing off the walls instead of screeching main bearings*), but the throttle is jammed wide open so I only feel comfortable running it for 2-3 seconds max, just as a confirmation that it will actually go. It appears to be something to do with how I've put the carb together (most likely, how the throttle needle assembly is going into it), but other than that I haven't a clue WTF. Any good ideas re: what I should look for when I revisit the scene? It goes in OK and I can do up the throttle top screw-cover, just when I turn the grip (or maybe before then?) it wedges open...

* when I hold the crank stationary with a breaker + socket and try to tug/push the conrod up and down, it's solid as a rock. But spinning the crank round makes a quite definite scrapey rubbing noise which the "new" bottom end doesn't exhibit. So, I guess main bearings? Not quite as hard to fix as big end?


Also I did briefly and very carefully pop the carb open, after draining it out, to see if I could alter the main jet at all (I figure it's running slightly too lean?), and I must admit I'm baffled. There's talk of moving things up and down on clips and the like, but the jet appears to be a single solid piece of machined brass with no clips or alterable parts whatsoever. Is this at all normal or has something come adrift somewhere? If it's par for the course with one of these, would my only recourse be to change the jet outright (for, I presume, the next larger number)?

And what's the throttle stop screw for, seeing as it just seems to be a peg that goes in and out when you screw it without having any clear way of thereby affecting the things that share its bore?
(I did put both of them securely back to the exact position they started from, btw. Not going to change the settings on something I so poorly understand at this point)
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tahrey
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PostPosted: 13:52 - 22 Oct 2012    Post subject: Reply with quote

Teflon-Mike wrote:


N2O...... on a CG...... for hills......... yup..... could work.......



Laughing
Sorry, thought exercises of putting nitrous systems on plainly unsuitable engines is just something that my brain does from time to time.

After all a +5hp kit shouldn't be too expensive and would use a pitifully small amount of gas. I could probably keep it on boost for a couple minutes at a time without too much worry... Rolling Eyes


Quote:

Honda CD200 the 15bhp, you want with 80+mpg potential, and the extra low and mid-range stomp to do hills and shit.


Agh! You're obsessed, man! Laughing
(*googles*)

I'm getting pictures of fairly cool looking bikes, but text to do with genetics and camcorders?! Internet fail.


Quote:

Better still CB250RS single, 31bhp 100mph potential and still 90mpg furgality,


I'm gonna need some proof of that one! Very Happy


Quote:

Probably enough to make up for the wopping extra £15 a year road tax you seem deturmined to try and avoid!


Let's say that's a challenge ceiling. It's keeping the exercise entertaining whilst the less interesting main business of actually getting the bloody thing back on the road in the first place carries on in the background.

Besides, I'm now left with a stock CG lower end, with knackered main bearings (IE it will need taking apart anyway to be usable again), onto which cheap and far more available top-end parts can be shoved if a strategy is found for making tab A fit into slot B, all the time whilst the rebuilt machine keeps trucking. It's the simplest way short of just tossing in the towel and taking a chance on something of much increased capacity (though 200 isn't too bad I guess).

It's not so much the money itself, just the principle of the thing. I'd like to get you into an argument with my mum, however, given how much of a strop she started to throw at me "wasting money" when I offered her the "spare" Lidl wireless doorbell I'd bought because she hates the one her house came with.
(I wanted to put two sounders at opposite ends of my flat, but they're only sold as full kits. Kits which each cost me... two quid.)

Quote:

There's a certain pervesity of shedology going on here, that is well beyond 'amusement' and long into the arena of self-delusion, mate!


You don't know where the limits are until you test them! And yes, they're closing in on me. But at least I haven't actually started hacking into the metal before figuring it out.

I do like to retain a spirit of optimism however, as I've been told on previous occasions "you can't do that" / "it won't work" etc, by others who also hadn't even tried the job, only for it to actually be fine. Including mating the dirtbike bottom end with my surviving top-end bits and having it run! (Or extending the gearing on the car beyond what popular skepticism said the engine would withstand ... only for it to be fine ... and manufacturers to actually "copy" the idea a few years after...) ... similarly in the electronic area Smile

It doesn't guarantee or even suggest success will actually be forthcoming, but at this point it doesn't absolutely guarantee massive fail (or even cost) either. How much do people pay for car and big-bike tuning chips that might give them, what, 5-10% extra power? Or intakes and exhausts with little provable benefit, etc?

(Thinking of exhaust "tuning" btw, as there are some reasonably flat straight isolated roads dotted round and about this borough, and I've now discovered just how easy it is to dismount the exhaust, I might grab some earplugs take it off and hide it behind a tree, and see what effect that has on my top speed vs a baseline run with it in place... better, as the much freer flow (literally directly out of the cylinder to the air) gives less resistance? Worse, as the oscillating pressure waves aren't sucking the gases out any more? No difference, because it's either completely ineffective either way, or has so little an effect it's not detectable vs that of a light breeze changing direction across the test course?)



Quote:

Kept in the cerebral, yes, its all quite interesting, but..... its a CG... it will ALWAYS be a CG, and the best thing about CG's is...... well, they are CG's!


I know I know... but if this one is going to have a habit of throwing shoes and being the runt of Honda's 2004 litter... in ways that may make it fit for scrap and of little resale value anyway... might as well satisfy a bit of curiosity with it.

I'll have to see how it behaves with this part in place, the closer ratio gearbox, and - hopefully not long after, as I now have the parts - the longer sprocket ratio... that might be enough, at least up top.
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Kickstart
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PostPosted: 19:34 - 22 Oct 2012    Post subject: Reply with quote

tahrey wrote:

Er... roughly... 150~200 square centimetres? The paper side (it's got one side paper the other size gauze) is indeed pleated, but the metal one isn't.

It's fed by, and then feeds down into a tube that's probably more in the 10-15 cm^2 range, however, and a carb with a smaller aperture still. Exhaust valve is nice and large at least Very Happy


A fair bit of the area of the filter is solid (ie, the actual material). Suspect 150~200 square cm is fairly high compared to a single filter.

tahrey wrote:
Ah, because it'll put more stress on the conrod joints I suppose? And 37mph is fairly quick if you're doing it within a small bore and changing direction a couple hundred times a second...

So the idea would be to try and keep the max piston speed about the same if possible? Maybe even requiring resetting the limiter "just in case" if it's stroked?


You can probably safely up it a touch probably, but be careful. It is mean piston speed, as the actual speed varies between 0 (at tdc and bdc) and something stupidly high between them

tahrey wrote:
1/ How much of a pain in the balls am I in for if there's a bolt stub stuck in one of the engine mount holes (don't ask me how, it came like that!) and nothing I have will touch it? I might get some harder drill bits (nothing I have at the moment is any better than HSS) and try it in something approaching a more professional fashion IE taking it slow and playing a hose on the drill site, but I'm not too confident. I ended up giving up on drilling out another one where the bolt had seized (managed to make a dent about 3 mm deep, if that) and just dremeled the nut into 3 pieces instead then whacked it with a hammer to break it off.


I would be inclined to use heat (and possibly something like a freeze spray carefully aimed to suddenly cool things). However I would also be tempted to try turning the bolt, but not sure if you have taken off both ends of the bolt.

tahrey wrote:
but the throttle is jammed wide open so I only feel comfortable running it for 2-3 seconds max, just as a confirmation that it will actually go. It appears to be something to do with how I've put the carb together (most likely, how the throttle needle assembly is going into it), but other than that I haven't a clue WTF. Any good ideas re: what I should look for when I revisit the scene? It goes in OK and I can do up the throttle top screw-cover, just when I turn the grip (or maybe before then?) it wedges open...


First thing to check is that the carb slide is in the right way round. On many carbs it will fit 180 degrees out but not seat properly and just be on full throttle.

tahrey wrote:
* when I hold the crank stationary with a breaker + socket and try to tug/push the conrod up and down, it's solid as a rock. But spinning the crank round makes a quite definite scrapey rubbing noise which the "new" bottom end doesn't exhibit. So, I guess main bearings? Not quite as hard to fix as big end?


Sounds right.

tahrey wrote:
Also I did briefly and very carefully pop the carb open, after draining it out, to see if I could alter the main jet at all (I figure it's running slightly too lean?), and I must admit I'm baffled. There's talk of moving things up and down on clips and the like, but the jet appears to be a single solid piece of machined brass with no clips or alterable parts whatsoever. Is this at all normal or has something come adrift somewhere? If it's par for the course with one of these, would my only recourse be to change the jet outright (for, I presume, the next larger number)?


The main jet is a set size. You adjust that by swapping it for one of a different size (or if you have some very accurate jet drills they can be increased in size, but don't even think about that!). The needle locates in the slide with a small clip and on many carbs you can move the clip onto a different groove on the needle. Move the clip to the sharp end to richen the mixture in the mid range and to the blunt end to lean the mixture in the mid range.

tahrey wrote:
And what's the throttle stop screw for, seeing as it just seems to be a peg that goes in and out when you screw it without having any clear way of thereby affecting the things that share its bore?
(I did put both of them securely back to the exact position they started from, btw. Not going to change the settings on something I so poorly understand at this point)


It pushes on an angled cutout on the bottom of the slide, so as it screws in the slide rests further up.

All the best

Keith
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tahrey
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PostPosted: 12:45 - 23 Oct 2012    Post subject: Reply with quote

Kickstart wrote:

A fair bit of the area of the filter is solid (ie, the actual material).


Ah, so the holes in it would likely overall be equivalent to the pipes going into the inlet?

Yknow, overall, I sort of feel there's a fairly good bit of breathing capacity left (aside from the "tuning" concerns). The air filter and main inlet/exhaust is a good fraction of the size of what my old 1-litre car had, and the pipework on the cylinder (and the valves) isn't much smaller than what each of its pots had.

...hmm, then again, though it was 8x the size, it did develop its power (and approx 1/2 as much of it per litre) at a little over half the rpms. So it's maybe about equal overall.


Quote:
You can probably safely up it a touch probably, but be careful. It is mean piston speed, as the actual speed varies between 0 (at tdc and bdc) and something stupidly high between them


Complicated maths may be involved ... but there's no way it'd be lower with a longer throw at the same revs anyway...


Quote:

I would be inclined to use heat (and possibly something like a freeze spray carefully aimed to suddenly cool things). However I would also be tempted to try turning the bolt, but not sure if you have taken off both ends of the bolt.


Unfortunately:

1/ I have blowtorched the everliving crap out of it and it wouldn't shift at all at any point in the process. I could probably nick a can of compressed air from work to act as a sort-of freeze spray, but think it likely wouldn't do much. Slightly worried about the potential effect of rapid heating and cooling on the block itself anyway.

2/ If that bolt and its hole are an exact match for the same one on my CG (as I very strongly suspect), then it's an unthreaded hole so turning really shouldn't do anything. As well as, given which end was sticking out, there isn't any thread in there anyhow. I have absolutely no idea how it's got stuck when what's in there should be a straight metal dowel, more or less. I have a feeling the donor bike was in a frame-mangling prang that partially pulled the head end of the bolt into the hole, either dragging a bent bit of head with it, or at least wedging the slightly flared part in a bore that's not quite wide enough for it.

The twisted remnant doesn't go all the way through, but starts about halfway in from the right-hand (clutch) side, and when I started work was poking out about 3cm from the left (alternator) side. And so it has largely remained.

3/ I did try turning it but it proved stuck utterly fast, and anyway...

4/ ...I have now cut it off (a centimetre at a time because of limited clearance) more-or-less flush (save a maximum of 1mm) with the casing. Strangely there is a gap around it where the bore is wider than the rod? This gap doesn't go in more than a centimetre or two. It might well be that there's a slight flare on each side so that it doesn't matter so much which way you put the bolt in? The other side is completely blocked from the halfway-ish depth without any suggestion of such an encircling gap.

Drilling it now appears to be my only option, unless someone can point me towards plans for a home-made thermal lance or an affordable high-hundreds milliwatt laser that can simply melt its way through the thing without having serious knock-on effects for the engine casing itself.


Quote:

First thing to check is that the carb slide is in the right way round. On many carbs it will fit 180 degrees out but not seat properly and just be on full throttle.


With what else you've written, but not having the Haynes to hand, I presume this is the plasticky sleeve thing around the needle that the spring appears to rest on top of? It goes in any which way round as far as I can tell, though as I didn't much disturb things other than undoing them and putting them to one side, I figured it probably would "naturally" go back in much the same alignment as it came out...


Quote:
tahrey wrote:
So, I guess main bearings? Not quite as hard to fix as big end?


Sounds right.


What might have caused that then? Simple high speed / poor lubrication abuse that somehow didn't also do for the big end, or something else?


Quote:

The main jet is a set size. You adjust that by swapping it for one of a different size (or if you have some very accurate jet drills they can be increased in size, but don't even think about that!).


No fear! They seem to be commodity parts so if I change it, I'll go by the conventional route of just buying a replacement.

Higher number = larger holes = more fuel = richer mixture, right?


Quote:
The needle locates in the slide with a small clip and on many carbs you can move the clip onto a different groove on the needle. Move the clip to the sharp end to richen the mixture in the mid range and to the blunt end to lean the mixture in the mid range.


Ohhhhhhh - so I should be looking at the throttle part rather than the "actual" carburettor part in order to adjust that?
(told you I was a noob when it came to these things - I'm much more comfortable with the idea of ECUs and map-ROMs Wink)


Quote:
tahrey wrote:
And what's the throttle stop screw for, seeing as it just seems to be a peg that goes in and out when you screw it without having any clear way of thereby affecting the things that share its bore?


It pushes on an angled cutout on the bottom of the slide, so as it screws in the slide rests further up.


One therefore presumes its function may become more clear if the slide is actually put in the right way round then? I think I recall seeing a diagonal slot on the slide (if that's what I was looking at), but it was just a hole in the slide wall rather than anything that projected inwards and so would cause it to move up and down as the peg went in and out.

Or is it supposed to have a more subtle range of adjustment, and the pointed end of the peg makes it turn one way or the other (and/or move up and down), with a large amount of the screw adjustment range actually not doing anything at all?

And which end of the range does it affect - limiting how wide "full throttle" is, or one part of the idle adjustment system? Allegedly these carbs aren't supposed to HAVE an idle speed adjuster, just a pilot mixture screw, which I already found and played with quite a while ago...

Ta Smile
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 23:25 - 23 Oct 2012    Post subject: Reply with quote

tahrey wrote:

Ah, so the holes in it would likely overall be equivalent to the pipes going into the inlet?


Something like that. It is why a tea strainer used as a filter over the end of a carb is actually pretty restrictive.

tahrey wrote:
Complicated maths may be involved ... but there's no way it'd be lower with a longer throw at the same revs anyway...


Aye, hence mean piston speed is used as an easy rough an ready guideline. About 25m/s is regarded as the absolute limit (ie, design everything from scratch to cope with the revs, etc, and that is the most that can be hoped for).

tahrey wrote:
2/ If that bolt and its hole are an exact match for the same one on my CG (as I very strongly suspect), then it's an unthreaded hole so turning really shouldn't do anything.


I would suspect the steel bolt has seized to the alloy of the engine, hence by turning it while heating it / clouting it from the other side you are more likely to free it off.

tahrey wrote:
With what else you've written, but not having the Haynes to hand, I presume this is the plasticky sleeve thing around the needle that the spring appears to rest on top of? It goes in any which way round as far as I can tell, though as I didn't much disturb things other than undoing them and putting them to one side, I figured it probably would "naturally" go back in much the same alignment as it came out...


The complete slide. A sort of tube, probably about 3/4 of an inch across and about 1.5 inches long. Likely has a cutout down one side that slides over a small pin on one side of the carb body.

tahrey wrote:
What might have caused that then? Simple high speed / poor lubrication abuse that somehow didn't also do for the big end, or something else?


Err, revving the nackers off it down hill with the wind behind you probably wouldn't do them the best of good Laughing . Poor lubrication wouldn't help but to be honest I would expect the big end to suffer first.

tahrey wrote:
Higher number = larger holes = more fuel = richer mixture, right?


Normally yes (can't think of a carb system that works the other way, but there could be one somewhere). Note that it is probably best to stick with the same supplier of jets if you do some fiddling. The flow rate is not 100% determined by the size (eg, there used to be plastic jets available for some carbs which would flow differently despite the same claimed size).

tahrey wrote:
Ohhhhhhh - so I should be looking at the throttle part rather than the "actual" carburettor part in order to adjust that?
(told you I was a noob when it came to these things - I'm much more comfortable with the idea of ECUs and map-ROMs Wink)


Yes. The mixture screw controls the mixture at idle and just off idle (up to about 1/8 throttle), the shape of the carb slide controls the progression from that to the needle (so about 1/8 to 1/4 throttle, nobody ever bothers to change the slide though) and the needle from about 1/4 to about 3/4 throttle. Main jet above that. Needles come in various different profiles, but starting point is to just adjust the clip on it.

tahrey wrote:
One therefore presumes its function may become more clear if the slide is actually put in the right way round then? I think I recall seeing a diagonal slot on the slide (if that's what I was looking at), but it was just a hole in the slide wall rather than anything that projected inwards and so would cause it to move up and down as the peg went in and out.

Or is it supposed to have a more subtle range of adjustment, and the pointed end of the peg makes it turn one way or the other (and/or move up and down), with a large amount of the screw adjustment range actually not doing anything at all?


It will have a range it works over, but will probably lift the slide about 3mm~4mm from fully out to fully in. That would make a massive difference to the idle speed. Probably 5~6mm of movement in / out of the screw to do this though.

tahrey wrote:
And which end of the range does it affect - limiting how wide "full throttle" is, or one part of the idle adjustment system? Allegedly these carbs aren't supposed to HAVE an idle speed adjuster, just a pilot mixture screw, which I already found and played with quite a while ago...


Honestly don't know but would be surprised if there was no idle speed adjuster.

All the best

Keith
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tahrey
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PostPosted: 12:12 - 24 Oct 2012    Post subject: Reply with quote

After some abortive fiddling last night, where I managed to run the battery down and badly piss off my hosts, things have become a bit clearer. Unfortunately I didn't get as early a start as I'd liked because my car decided to throw its toys out of the pram in the work car park also... Nor did I get to buy any hardened drill bits...

Good news however is the engine is running and controllable, and with the battery on charge all I should - theoretically - have left to do is (after attempting a bit of drilling) tighten up the mount bolts that are currently in place, pop the hose clips on, fit the chain/pegs/gearlever/seat, realign the pillion peg mounts, properly fit the exhaust, and GTFO of the garage before I'm taken off the christmas list... Everything else (bulb and sprocket swaps etc) can be done at home in the unlit/unheated/unpowered/no-running-water garage Smile

Quote:

Aye, hence mean piston speed is used as an easy rough an ready guideline. About 25m/s is regarded as the absolute limit (ie, design everything from scratch to cope with the revs, etc, and that is the most that can be hoped for).


That IS about 1.5x higher, though Smile

Huh ... so ... just how short a stroke / wide a bore do the bikes (and race engines) that rev up to 17~18000 rpm have then?


Quote:

I would suspect the steel bolt has seized to the alloy of the engine, hence by turning it while heating it / clouting it from the other side you are more likely to free it off.


Turning isn't really an option any more. Did heat it and batter it pretty hard though. I used the already-mangled rear mount bolt I bought a replacement for as a drift and battered the shit out of it first with a hard rubber mallet and then a steel claw hammer. The end of THAT bolt ended up pretty badly splayed (only just got it back out!), but the wedged part didn't seem to move a millimetre.

I'm just going to resort to carbide drill bits, and if that doesn't work, seeking professional help.


Quote:
tahrey wrote:
With what else you've written, but not having the Haynes to hand, I presume this is the plasticky sleeve thing around the needle that the spring appears to rest on top of?


The complete slide. A sort of tube, probably about 3/4 of an inch across and about 1.5 inches long. Likely has a cutout down one side that slides over a small pin on one side of the carb body.


That's the bunny. Seems that once again my observation and memory are somewhat fail. But I was rather tired and rushed in a not brilliantly lit location (some bright spark had the idea to light the garage with a 3-way rosette of halogen downlighters instead of a nice long fluorescent strip ... and one of the sockets has burnt out. No, not the bulb... the socket).

Examining it more closely and carefully it's a bit more solid than I thought, and there IS a diagonal cutout that goes from the outer edge in towards the needle. And that/the screw ARE responsible for idle control.

Dicked about for ages trying to get it in. Ended up having to disconnect and take the whole carb back off to have a better play. Turns out there's a plastic guide peg for the back side of the slide (where the throttle cable also attaches) and one part or the other must be slightly burred, as it took a harder shove than what even the spring could provide to push the two parts past each other.

After that, it slid home just nicely - much, much further down the bore than any previous time (like about 1 1/2 inches!) - and operated exactly as it should have. Got it back on the bike and (after ten minutes of juicing up the already flattened battery) it fired up and idled just fine. Except at rather low revs following my messing with the idle screw trying to "get it out of the way" (not quite understanding where it was in 3D space), eventually stalling, with a subsequent restart attempt re-draining the battery.

Gave up for the night after tightening a couple of token minor bolts and re-setting the carb pipe clips and left the battery to top off.

I think I'll cock about with the needle setting some other time. Had a quick go at unhitching the throttle cable and thanks to how things moved and felt I got the fear that I might not be easily able to reattach it post-adjustment. Will leave that one for the chrimbo hols perhaps.


Quote:

Err, revving the nackers off it down hill with the wind behind you probably wouldn't do them the best of good Laughing .


I know, but it was definitely warm at that point and I didn't do it on that regular a basis Smile --- those actual motorway dash incidents were a fair way in the past compared to recent rides.

I did tend to end up on quick-ish roads in less than 5 minutes after starting, but I did have a mind towards that and didn't rev so hard as I otherwise might have (ah the benefits of torque Very Happy)


Quote:
Poor lubrication wouldn't help but to be honest I would expect the big end to suffer first.


Exactly, that's what's baffling me. Not that I'm ungrateful for it being an easier-than-expected fix, but it didn't make the diagnosis ever so easy and it doesn't make much sense either...


Quote:
Note that it is probably best to stick with the same supplier of jets if you do some fiddling.


Got it, ta!

Quote:

the shape of the carb slide controls the progression from that to the needle


This one looks like it mirrors/matches the curve of the actual carb inlet, so producing an actual "tube" that changes from a narrow eyeslit to a fully circular cross section. Seems fairly optimal to me, really. What other kind of shapes would you have anyway?


Quote:
Needles come in various different profiles, but starting point is to just adjust the clip on it.


That'll certainly do for now, as my only guess at diagnosing why it suddenly stalls out below a certain rpm with wide/full throttle is that it's either a bit too lean or a bit too rich, both of which are things that would be good to fix at high rpm / full throttle also.

Though I don't think it's out by much. It might just be that it is in fact optimally set and the carb itself just can't cope with full throttle in low-flow conditions for whatever reason. The piston crown and the combustion chamber/valves were fairly clean but not shiny. A little bit of surface carbon that came off very rapidly with just a small dab of dilute oven cleaner, suggesting very good (even if not actually "perfect") adjustment.

Not bothered if it still won't pull all the way down to idle afterwards, just so long as it's a little smoother and more reliable at around (20-)25-30mph in top.


Quote:

It will have a range it works over, but will probably lift the slide about 3mm~4mm from fully out to fully in. That would make a massive difference to the idle speed. Probably 5~6mm of movement in / out of the screw to do this though.


Given how far the screw moves, and the actual height/depth of the cutout now I've looked at it, there might be a good centimetre of adjustment available! Certainly after I'd moved it out a little (not fully out by any means), the engine could barely sustain a shaky tickover, and eventually cut out.

I'm just trying to figure out, now, how it gets any air at all when the choke's closed - purely out of interest rather than for any practical purpose (at least at present!). The flap seems to shut off the main bore entirely on full choke. There are a couple of teeny-tiny pipes that might be bypass ports (maybe?), but they're so small I can't see how the engine would be able to run at anything more than a slightly fast idle producing maybe a couple hundred watts net power, never mind still be capable of sustaining at least 40mph (4-5hp?) at moderately high revs. The restriction on half-choke (which is more like 3/4s if anything) should be enough to cause that much power loss...
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tahrey
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PostPosted: 00:26 - 25 Oct 2012    Post subject: Reply with quote

Roit! It's basically back together Dance!

Almost all the parts are where they should be and bolted in place. The engine starts and runs quite nicely. Exceptionally nicely in fact - it's so, sooo much quieter I can hardly believe it. The looseness in the bearings must have somehow made every part of the engine noisier, right down to the exhaust note - and it must have been getting worse for a lot longer than I realised (heck, maybe since before I bought it?) because I can't even remember it being this subdued. It ticks over like a timid sewing machine now, when it was quite raucous before even if you ignored the actual bearing noise. It even revs in a polite and modest fashion.

Haven't had chance to try drilling the stuck bolt, as my stopping by Toolstation (my new favourite supplier, not least because they sell 105-watt bayonet fitting halogen lightbulbs and give you free coffee) to pick up some Cobalt-steel drillbits and cutting fluid (learnt my lesson, did my research) meant I turned up at casa mama late enough that she didn't want me plugging the drill in.

So that's one job that'll have to wait for now. At least almost everything else is done.

I did however find two rather minor parts didn't quite go back together right for some reason.

First of all, one of the footpeg bolts simply refused to screw all the way into the bore as deeply as it needed to, no matter how I seated or threaded it. I can only assume either the hole is shallower, or whatever mishap wedged the errant bolt in the mount hole also stripped/mangled the thread below a certain depth. As the bar was already held on pretty tight by the other two, I just shimmed the last couple millimetres with some random roughly-the-right-side washers and had done with it. I'll just have to make a mental note not to try bunnyhopping it in anything except an emergency any more.

Secondly, well...

Turns out the only part that isn't directly cross compatible between the CG and XR is the front chain sprocket. The spline ribs on the gearbox output shaft are about a millimetre (if that) wider on the XR, meaning that neither the old or brand-new CG sprockets will fit on it. (T'other way round, an XR sprocket might have been a bit loose on the CG shaft, but could at least have been used to carefully limp the thing back home)

What the fuck, Honda?

So, it's not going anywhere until I can get another, XR compatible sprocket ordered up. I will also have to double check that they do actually use the same chain pitch, I guess? If they're not available (or at least, not available with the right number of teeth / right chain pitch) I'll probably just have to try shaving down the inner tangs of the CG sprockets to fit.

Strewth. I need a beer.

Mood at the moment:
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tomh
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PostPosted: 09:51 - 25 Oct 2012    Post subject: Reply with quote

Nice to hear your CG is nearly fixed. I had the same problem when removing my engine. Two of the bolts had corroded and seized inside the engine. A large rachet and lots of plus gas still managed to snap the head of the bolt.

We used a large punch, hammer and heat to get it out. It took so much heat from the torch that the crankcase has lots of bubbling marks although thankfully the gasket doesn't leak. I was thinking of drilling myself but really without a pillar drill and the engine in a jig it's going to be very hard to drill straight all the way through.
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kramdra
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PostPosted: 11:49 - 25 Oct 2012    Post subject: Reply with quote

Yeah, the bolt, you just need a bigger hammer. Id start with a 1kg club hammer to move most things.
If not, 6kg sledge hammer, used with a lot of care, will move anything else... although getting the rusted spindle out of my rear wheel did take the full force of the sledge, eventually it was out.
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Kickstart
The Oracle



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PostPosted: 00:11 - 26 Oct 2012    Post subject: Reply with quote

tahrey wrote:

That IS about 1.5x higher, though Smile


Aye, for the ultimate limit for things designed for it, not things designed to be cheaply lobbed together.

tahrey wrote:
Huh ... so ... just how short a stroke / wide a bore do the bikes (and race engines) that rev up to 17~18000 rpm have then?


Very short. Ducati 1199 has a 60.8mm stroke (and a 112mm bore!), and that revs nowhere near that high.

tahrey wrote:
I know, but it was definitely warm at that point and I didn't do it on that regular a basis Smile --- those actual motorway dash incidents were a fair way in the past compared to recent rides.


If you are over revving it that far whether the oil is hot or not is probably the least of your problems!

tahrey wrote:
That'll certainly do for now, as my only guess at diagnosing why it suddenly stalls out below a certain rpm with wide/full throttle is that it's either a bit too lean or a bit too rich, both of which are things that would be good to fix at high rpm / full throttle also.


Don't give it full throttle at low revs

All the best

Keith
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tahrey
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PostPosted: 15:45 - 26 Oct 2012    Post subject: Reply with quote

kramdra wrote:
Yeah, the bolt, you just need a bigger hammer.


Isn't it always the way...! Brick Wall
Miiiiiiight have a 2lb lump hammer sitting around somewhere, but I think that's about the limit. I'm not physically burly enough to accurately wield anything much bigger anyhow, not with the engine sitting in the bike rather than on a nice convenient bench as it was when I did the other work.

(well, on a nice convenient, borrowed Black and Decker workmate, whose load/impact ratings I wouldn't dare to test anyhow!)


TomH wrote:
It took so much heat from the torch that the crankcase has lots of bubbling marks


Shocked

Quote:
without a pillar drill and the engine in a jig it's going to be very hard to drill straight all the way through.


Well, either later tonight or sometime tomorrow, I'll give it a bosh with the cobalt bits and cutting fluid. Might actually go in from the "far" side - seeing as the rod part of the trapped bolt has clear air all around it, I might only need to clear a fairly short distance to free the thing, then it's a matter of just clearing the bore to a sufficient width for the replacement bolt to squeeze through.


Kickstart wrote:
((1.5x higher MCV))
Aye, for the ultimate limit for things designed for it, not things designed to be cheaply lobbed together.


I suppose ... there's usually some leeway in the system though, right?

Quote:
((how short are the strokes?!))
Very short. Ducati 1199 has a 60.8mm stroke (and a 112mm bore!), and that revs nowhere near that high.


Daaaamn.

Though I would think so too given that that STILL gives it a longer throw than I was considering extending the CG to, and it craps out around 10~11,000...

Quote:
tahrey wrote:
I know, but it was definitely warm at that point and I didn't do it on that regular a basis


If you are over revving it that far whether the oil is hot or not is probably the least of your problems!


Hey, now, I didn't take it beyond what the manufacturer intended. It's got what some might call a relatively conservative rev limiter (10500? 11000? rpm...), possibly partly because of the lack of tacho to give any other overspeed warning, so little power near the limiter that the indicated ~83mph (really more like 78-79) was probably at least 50% down to the gradient and slipstream, but enough that when the ignition started to cut at the limit it certainly wasn't going to go any faster.

Then a handful of seconds later we reached the bottom of the hill, which was a short cut-out valley under a surface-road bridge, and went into the slight incline and sharp right hander that followed it, meaning speed dropped right off and almost immediately back into the 60-65 zone.

The section BEFORE that downhill was a 3rd/4th gear thrash up a steep sliproad, just catching 5th at the point of merging into lane 1, then grinding up and over a reasonably substantial climb at 55 ... 56 ... 57... 57.5 ... 57.75..... mph Wink

S'not like I was holding it at supra-limiter speeds for hours or even minutes on end, or doing it within the first five minutes of starting up at 7.30am on a freezing monday.

However, it is a low-geared machine as standard, which means just cruising in the 60s is probably a risk factor, hence my intent to gear it up and see what happens. On that front, the front sprocket (AND CLIP AND BOLTS... I'm not that much of an eejit Very Happy) I'm waiting for WeMoto's courier to drop off at work's reception desk is a 15t, instead of the 14t came off the CG. And I already have a 44 to try and get on the rear wheel at some point in the near future. Hopefully it'll improve rather than ruin the performance and cruiseability.

(Also going to lobby my MEP to try and make it so, even if the "only big bikes may be modified" legislation goes ahead, those of us with Proper Licenses will still be allowed to derestrict and alter the gearing of our sub-60hp / post-2012 machines...)


Quote:
((poor low rpm performance))
Don't give it full throttle at low revs


Well, that's the simple solution to the problem, and what I've done so far anyway (along with being generally progressive with winding the throttle on in all situations), but any technical reason for it other than "if it stalls at low rpm and full throttle, don't give it full throttle at low rpm"? It smacks of poor tuning to me, unless it's an intrinsic feature of this kind of carb.

I mean, I was able to get at the jet without too much hassle, as well as remove and replace it, so if they're fairly cheap and easy to get hold of it doesn't seem like that potentially damaging or expensive an experiment to conduct. Ditto the needle clip, now I've been clued in to where it actually is Wink

Ta much Wink
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 18:57 - 26 Oct 2012    Post subject: Reply with quote

tahrey wrote:

I suppose ... there's usually some leeway in the system though, right?


Aye, abit. But nowhere near enough for a CG125 to go from ~16m/s to anything close to the ultimate limit.

tahrey wrote:
Though I would think so too given that that STILL gives it a longer throw than I was considering extending the CG to, and it craps out around 10~11,000...


It probably also has a far better design of rod, with better finish, well designed piston, conrod length chosen to match the stroke rather than just lobbed in to help stretch the stroke, etc.

tahrey wrote:
Hey, now, I didn't take it beyond what the manufacturer intended. It's got what some might call a relatively conservative rev limiter (10500? 11000? rpm...), possibly partly because of the lack of tacho to give any other overspeed warning, so little power near the limiter that the indicated ~83mph (really more like 78-79) was probably at least 50% down to the gradient and slipstream, but enough that when the ignition started to cut at the limit it certainly wasn't going to go any faster.


Think the speedo is marked with max speeds in each gear. Which work out as having a red line of about 9000rpm. So revving to 10500 is a long way into the red line.

tahrey wrote:
S'not like I was holding it at supra-limiter speeds for hours or even minutes on end, or doing it within the first five minutes of starting up at 7.30am on a freezing monday.


It is still massively over revving the engine. Entirely possible to blow up an engine from over revving with a split second (eg, guy I know racing a car had a drive shaft pop out while cornering hard, and the revs went through the roof and blew the engine before he could get off the throttle).

tahrey wrote:

Well, that's the simple solution to the problem, and what I've done so far anyway (along with being generally progressive with winding the throttle on in all situations), but any technical reason for it other than "if it stalls at low rpm and full throttle, don't give it full throttle at low rpm"? It smacks of poor tuning to me, unless it's an intrinsic feature of this kind of carb.


It is a slide carb. Opening it wide up at low revs means you are running on the main jet with barely any air flow through the carb. Fit a larger carb and the problem will get worse, and why CV carbs became so commonly used despite normally giving less power.

All the best

Keith
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tahrey
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PostPosted: 13:20 - 28 Oct 2012    Post subject: Reply with quote

Kickstart wrote:

Think the speedo is marked with max speeds in each gear. Which work out as having a red line of about 9000rpm. So revving to 10500 is a long way into the red line.


Mine doesn't have the gear range marks on the speedo, as it's got electronic ignition and therefore the max engine speed is determined by Honda and the circuitry they put in the box, rather than either "however high it'll rev whilst still producing surplus power" or being limited by a commonly somewhat bendable mechanical governor in the points.

As peak power isn't until 8500~9000 depending on model (I think mine might be the latter) it seems odd that the redline would also be there. It means you can't actually get full power out of the engine without over-revving it? Why would you build your engine that way? And why set a rev limiter that's so high you still end up damaging the engine if reaches that speed, whilst warm, for any length of time? It doesn't make any sense. This bike is allegedly built to withstand massive abuse, which I would consider may also include thrashing it against the revlimiter in first gear up a third world mountain track with a heavy load on. If I then took it down the other side of said mountain, with that load on, using the engine braking in first and hitting 30+mph in the process, THEN I might expect the big end / conrod / pushrods to suffer some damage.

The fact that mainbearings gave out whilst the big end was still fine (and the pushrods completely straight) also makes me wonder if there was something wrong with them or if they received damage another way. They're under a bit less load than the other parts after all.

Also when I've seen them used elsewhere, speedo markings tend to be a bit conservative, probably because they're taking the place of the revlimiter and are using the human operator (a device known to be quite unreliable when it comes to sticking to limits, and prone to pushing the boundaries) as the primary means of limiting engine speed.

EG my VW had the shift points marked such that you would be pulling no more than 5000rpm - but the engine's peak power was itself at 5200, and the revcounter + limiter equipped models had a redline at 6000 and limited around 6500. To reach the listed top speed (should you be on an autobahn) vvould have rekvvired sitting at an engine speed in the lovv 5000s in 4th... something they presumably didn't think vvas an issue because there vvere only markings on the dial for 1st, 2nd and 3rd.

Then again the marked CGs do seem to show 5th being good for about 70mph...

All the same, knowledge and concern of much of the above is why I want/ed longer gearing in the first place...


Quote:

It is still massively over revving the engine. Entirely possible to blow up an engine from over revving with a split second (eg, guy I know racing a car had a drive shaft pop out while cornering hard, and the revs went through the roof and blew the engine before he could get off the throttle).


It's not though. It might have gone 5 or 10rpm over the electronically limited engine speed at best, for a mere fraction of a second (two or three turns of the crank). It's not like I even pulling 11500 (vs an 11000 limiter) let alone 12000, 13000 etc. It's not even like the effect of accidentally going down a gear during an overtake instead of up, something I've done in a previous car without long term damage resulting (obviously as soon as I realised, in a split second, I hit the clutch and pulled over... it did something like 8000 vs a 6000 limit/redline but survived ok)

If you have something like what you describe happen, then you're probably looking at a terminal rpm several thousand above the limiter speed, or possibly even briefly double whatever the engine was revving to start with, naturally causing massive and instant damage to it by things going snap. Plus that's a race engine that shaves a lot closer to the absolute engineering limits in the first place.

Quote:

It is a slide carb. Opening it wide up at low revs means you are running on the main jet with barely any air flow through the carb. Fit a larger carb and the problem will get worse, and why CV carbs became so commonly used despite normally giving less power.


Knowledge and experience - 1
Me - 0

well there you go then. Very Happy

Anyhoo my external keyboard just died on me making typing both e's, vv's and kyoo's rather difficult and longvvinded (I can at least map e to ctrl-v and do double-v's...), and I need to pop to homebase or somevvhere to get a drill cutting/grinding vvheel, so I shall bid you anon Smile

(another thing that doesn't match betvveen the tvvo bikes - hovv far out the front sprocket shaft sticks from the casing. so the chain ends up rubbing slightly on the chain guard support (managed to bend it sufficiently AND still have the guard held on OK, yay)... aaaaaaaaand the sprocket cover vvon't go on because there's some tubular bit of moulding vvho's purpose I can't fathom that ends up rubbing on the sprocket. Given that my choices at this point are 1/ ride vvithout and probably lose a toe, 2/ order up an XR cover off ebay and vvait for ages before fitting, 3/ attempt this and either succeed, or fail and have to do 2 anyvvay, I'm trying to trim a fevv millimetres off said moulding's height, but the tools vve have available just aren't good enough.
Also the stuck bolt, I am leaving as-is and vvill have a professional look at sometime soon. The bike is independently mobile and rideable and seems to hang together at least, but four bloody hours of careful drilling vvith cobalt bits and cutting oil managed to shave... oh... 5mm off the thing? VVith no improvement viz. actually getting it out? It might need as much as another 30mm grinding out, and I have no desire to spend 24 straight hours plugging avvay at it...)
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Kickstart
The Oracle



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PostPosted: 13:37 - 28 Oct 2012    Post subject: Reply with quote

tahrey wrote:

Mine doesn't have the gear range marks on the speedo, as it's got electronic ignition and therefore the max engine speed is determined by Honda and the circuitry they put in the box, rather than either "however high it'll rev whilst still producing surplus power" or being limited by a commonly somewhat bendable mechanical governor in the points.


Most vehicles with rev limiters have them well into the red line. Doesn't mean it is safe to scream them into the red under load. OK doing it occasionally might not be suddenly catastrophic but that doesn't mean it will do no damage at all.

tahrey wrote:
And why set a rev limiter that's so high you still end up damaging the engine if reaches that speed, whilst warm, for any length of time? It doesn't make any sense.


Forget being warm. Temp isn't really going to change sudden damage, just greatly increase wear if cold (ie, oil not yet circulated and / or clearances all over the place). Bigger thing they prevent is sudden over revving if you miss a gear change and land up in a false neutral. And then there is next to no load on the engine.

tahrey wrote:
The fact that mainbearings gave out whilst the big end was still fine (and the pushrods completely straight) also makes me wonder if there was something wrong with them or if they received damage another way. They're under a bit less load than the other parts after all.


Unlike the big end and little end, they are also rotating at engine speed rather than just back and forward.

tahrey wrote:
Also when I've seen them used elsewhere, speedo markings tend to be a bit conservative, probably because they're taking the place of the revlimiter and are using the human operator (a device known to be quite unreliable when it comes to sticking to limits, and prone to pushing the boundaries) as the primary means of limiting engine speed.


More taking the place of the red line, NOT the rev limiter. Also if they are shift points (rather than the max speed in any gear) they probably relate more to peak power, peak torque, fuel economy or something like that

tahrey wrote:
It's not though. It might have gone 5 or 10rpm over the electronically limited engine speed at best, for a mere fraction of a second (two or three turns of the crank). It's not like I even pulling 11500 (vs an 11000 limiter) let alone 12000, 13000 etc.


No, but you are already 1500rpm beyond the point Honda red line it, and revs it is safe to take it to on a regular basis. You are doing 10500~11000rpm against a safe 9000.

tahrey wrote:
If you have something like what you describe happen, then you're probably looking at a terminal rpm several thousand above the limiter speed


Possibly, but also under pretty much zero load unlike your engine which is doing well above max rev while also under heavy load.

tahrey wrote:
(another thing that doesn't match betvveen the tvvo bikes - hovv far out the front sprocket shaft sticks from the casing. so the chain ends up rubbing slightly on the chain guard support (managed to bend it sufficiently AND still have the guard held on OK, yay)...


That is a BIG issue if I am reading you correctly. The chain will be out of line between the front and rear sprockets. You can get offset sprockets (possibly even a standard one from another bike).

All the best

Keith
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