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| lozza59 |
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lozza59
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lozza59
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| Teflon-Mike |
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Teflon-Mike
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 Posted: 00:35 - 06 Aug 2011  Post subject: |
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Top one is a Duplex chain & standard to early; as in twin shock CB125's and ALL the later TD models.
Lower chain is a Hi-Vo rollerless chain, not a duplex.
It has no rollers, plates engage with teeth on sprocket directly. Supposed to run more quietly & stretch a bit less, and take a higher load; but also more friction and more weight and not like such high revs.
NOT fitted to CB engines, but WAS fitted to CA Rebel engines.....
Are you SURE that the crank from 'later' CB125 is a 180 degree crank, and from a CB engine? NOT a CA Rebel?
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?' |
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| lozza59 |
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lozza59
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| Posted: 01:32 - 06 Aug 2011 Post subject: |
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thanks for your reply Mike i have been hoping to hear from you 
the top chain 'duplex' is from a honda cb 125 180 crank
and the other is from a jialing jh 125 33 which also is a 180 crank
but i do not wish to use the jialing crank being chinese and so i asked someone breaking a 88 cb 125 which chain theirs took and they confirmed it to have only 1 crank sprocket.
preferably i would like to keep the original but the bearing between the 2 rods makes a horrible noise when i spin it and the rods move considerably from left to right, more so than the jialing which also has a much quiter bearing when spun,
the engine has always had a loud whirring noise since i had it which i thought was the cam eating into the head but i changed the cam and bearings and head and it continued to make the noise so now im thinking it could be the crank which is why i dont want to put it back in as it is.
also your rebuilding 2 cb motors right? what else have/are you replacing whilst its in bits?
can the crank and con rods bearings be replaced?
thanks again |
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| Teflon-Mike |
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Teflon-Mike
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Posted: 17:21 - 06 Aug 2011  Post subject: |
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| lozza59 wrote: | thanks for your reply Mike i have been hoping to hear from you |
Been on hols 
My rebuild saga is confusing. Started with simple engine swap from the breaker into the corporal. That worked, but badly, so it got top end; new barrel, pistons & head overhaul.
Worked a treat. So shifted attension to 'The Black One', which came in a rally nice T&T'd bike, with non running engine, diagnosed as 'low compression' by bike shop before being flogged spares or repairs.
Intention was to do a 'top end' on that one, same as engine that went into the corporal.
MEANWHILE; running the Corporal about following Snowie, training, engine dropped it's cam chain.
So, finished top end on the Black-One. Low compression was due to gummed rings, and having been run on gummed rings, so excessive bore wear and scored pistons.
New barrel kit, sorted that nicely; all I did on top, while it was open was strip head, grind valves and replace stem seals. And timed it all in nicely, discovering that if you have a 'good' cam chain, its a damn site tighter and hence harder to time in than it was doing the donor engine that went into the Corporal!
So, That 'Done', I stripped the engine from the 'scrapper' that had been in 'The Corporal', with new barrel on it, & dropped cam-chain. It was ' a bit of a mess'.
To make 'good' I stripped the 'original' engine from the Corporal, which had come in reported as 'seized'.
It wasn't, but it wasn't exactly 'nice'. I'd freed it off and run it up, but it had sounded like a bag of spanners in a tumble drier. Hence fitting better sounding lump from the scrapper, than messing with it, first time round!
Intended to try and make one 'good' engine from parts from two duffers; and since numbers on Corporals original engine matched frame numbers, chose to use the original cases to build on.
Crank from scrapper, was 'OK'. Crank from Original lump, was sloppy on No1 big end, but ran ok on mains. Cam journals had 'gone' though.
Original engine's barrels weren't too bad, and cam chain was serviceable.
But, Scrappers engine, piston had touched valves on No2, and when I attempted to remove inlet, bowed stem cracked guide.
So I used Original engine's head, with scrappers rocker gear and cam. Decided to use brand new barrels and cam chain as precaution, and used 'good' cam from scrapper in original engine's cases, with that motor's gearbox, after inspecting drum and forks and gears and deciding that there was no real difference between them, and both looked remarkably good.
THAT mongrel of two engines has just gone back into the Corporal, and is running pretty well, but I only had about an hour to fettle carbs, before holiday, so not running as well as it ought to yet.
Manwhile; Snowie came back from ASDA at 2mph, one day, the slight blue fug from No1 pots exhaust having become a white out!
So, suspect her engine had gummed up and done what the lump in 'The Black One' had....
So she STOLE the engine I had rebuilt for 'The Black One'.... meaning I have to sort it for her to get it back!
And there is the Benley engine, to be 'played with'.
THAT about sums up activity on Super Dream engine's to date.
YOUR query about crankshafts;
They are a 'pressed up' crank. Rather than being a single bit of metal, either cast or forged, with bearing journals ground on it, and then having cased and con rods clamped around the journals; its made like a push-bike crank.
Each cylinder has two fly wheels, with a central 'main' journal and an offset big end journal, formed by pressing over sized pins into under sized holes in the fly wheel, to form a bog off tight friction joint or 'interference fit'
Means that the con rods and bearings they run on are fitted to the crank pin before the crank is pressed together.
Bearings being pure radial roller races, not split 'plain' shells, con rod being solid item, not split with big end main cap.
Likewise, inner main bearing, and baring housing, were fitted to crank journal before pressing up.
ALL 'can' be dissassmbled, and overhauled, but..... NOT a job for you to try in a garden vice with lump hammer and drifts!
M/C shop job, crank properly supported in blocks, on a ten ton hydraulic press, for preference!
'Precautionary' replacements?
I was very careful rebuilding Corporal's engine not to 'mix' bearings from different shafts; either in the gearbox, or on the crank or cam.
Only bearings that could 'easily' be replaced on the crank are the outer two mains.
This IS commonly 'done', but I wouldn't.
Crank is supported by three bearings that SHOULD equally share the crank loading and wear pretty much equally.
IF the outers are so worn as to require replacing, then middle will too, right?
But THAT demands pressing the crank.....
If you fit, NEW outers and LEAVE the old middle in, what do you get?
Well, wear in the center bearing, will man that under load, either the centre baring, having more 'wear' and hence running clerance, is going to NOT take its share of the load, OR under load the crank will have to flex slightly to take up the extra wear clerance on the centre journal.
Flexing, it will skew not only the crank but the con rod and bearings, and is likely to induce vibration, AND stress the interference fit pin joints in the crank....
IE: to my sense of engineering asthetics, mixing new and old bearings, particularly on a crank is likely to MAKE more problems than it solves...
Life of crank assembly ULTIMATELY is that of the shortest living component, right? So, if you have 'old' middle main, with a certain 'life' left in it, THAT is the life of the crank, and fitting newer outer mains, with more life in them wont find you any 'extra' life.... just man that when the center finally gives up, you have two part worn bearings with life left in them on the end.
Was always tought before Studying Mech Eng at Uni; ALWAYS change bearings on a shaft as a set, never individual bearings. Uni, explained better why, from the point of view of loadings and stresses.
Only 'niggle' pint is the cam bearings.
These are prone to 'going' is starved of lube. & They are a 'plain' bearing, basically a bush with a hole for pressurised oil feed, the hardened cam journal running directly on the 'white-metal' of the cam cap.
Analogy here is rocker assemblies; on car engines, common when the rocker gear wears to swap out JUST the rocker shaft, rather than replace rockers or attempt rebushing them. Mainly because a rocker shaft will be somthing like £10, where you have eight rockers, at something like a fiver a piece, or £40... so swapping the £10 shaft you remove, 'notionally' half the wear, and save 4/5th the cost.
In practice though, hardned steel shaft wars less than softer white metal or phosphur bronze bushing metal... so you don't remove quite half the wear, AND, softer bush material 'picks up' the hardened steel 'swarf' from wearing the 'old' shaft... so when you fit new one, old soft bushd rubbing on it, wear it out quicker, and you end up in the same place as you were not much after.....
In the case of the CB125 Cam, though, we're talking about replacing the soft cam caps, so more likely to remove half the wear, and not so likely to induce accelerated 'swarf' wear, so not SUCH a bad call.
BUT.... how far do you chase it? You will still have war on cam journals, but the more 'critical' regions of wear will be on the cam lobes and in the rocker and rocker shaft journals.
Cams wear more on the ramp and peak of the load, when they have the force of valve springs pushing the rocker arm or follower against them, than they do on the base circle. Hence cam war will rob valve lift, and (though negligible in comparison) will tend also retard cam timing and shorten duration.
Wear on the rocker shaft is also asymetric, and you will get more war on the 'lift' than on the 'rock'... which is where you set valve clerances...
SO.... if the bearing caps are 'gone'.... new ones may only be a 'get you by' at best, to eek out a bit more life from worn out cam.
IF they aren't gone.... is it 'worth while' JUST replacing the caps?
My conclusion was, no, it wasn't. Lifan Caps are on -bay about £15 a piece, so £30 a pair, which is only £5 cheaper than replacement cam, which comes with cam caps.... so IF a precautionary is worth anything at all, might as well spend the extra fiver, and gt the new cam.
Which brings us to the matter of LIFAN BITS
Delibrating whether to use your Lifan Crank, I think I'd go with it.
Bottom line is, they aren't THAT bad, and most aftermarket parts being offered these days are coming out of the Lifan subbies, unless you go to OE Honda spars and pay through the frigging nose!
New Lifan crank assembly, or Barrl Kit or Cam Kit, to my mind, might not have the full 'life' of a genuine Honda replacement part, BUT darn sit MORE life than what you got, or likely to find second hand.
The CB125 Super Dream does NOT have a wonderful reputation for dependability or life to begin with. Bikes tend to run to about 20K-25K miles before problems creep in.
Badly looked after, neglected, thrashed, or left 'derelict', they can do themselves harm in under 15K, but even well looked after they will struggle to last 35K mils before needing major overhaul.
Chinky Fakeaway reputation is overly maligned, Gen-Jap, overly aplauded, in general, somewhere between lies a 'truth', possibly slightly closer to the lore than 'not', BUT, Lifan motors seem to be getting put into the better regarded Chinky bikes, and they aren't lasting 'as well' as hoped, but more often its cycle parts and electrics that are the problem than the engines....
SO, still your call, but worth a little thought..... ultimately cost of pressing a crank or buying gen Honda replacement I think will sway using what you got from the Lifan!
ONLY caution, I might offer, is that the early CB125's were 17bhp bikes, and components were rated to that power.
Last of the line CB125TD-E was only ever rated to 12.5bhp, and the CA rebel was detuned from that, by single carb, and its those two bikes that were 'blended' to crate the Lifan derivative.
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?' |
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| lozza59 |
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lozza59
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| Posted: 22:01 - 06 Aug 2011 Post subject: |
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thankyou Mike thats helped me make up my mind.
i also had a good laugh reading about the loss of your rebuilt engine i hope Snowie has better luck with the rebuilt motor,
i am going with the lifan crank as i could do with saving the money i may even use the cam chain, the motor only had 2,000 ish miles on the clock,
here is the crank i was interested in
https://www.ebay.co.uk/itm/HONDA-CB125T-CRANK-/260827780093?pt=UK_Motorcycle_Parts&hash=item3cba8c13fd
i have purchased from the seller before and the parts are great and also very cheap so i do believe the mileage of only 7,000 to be accurate, a very helpful ebayer too. though the crank has only 1 sprocket when i asked them, but from looking at the pic i can see its a 180 crank...
thanks for the info 
hope you had a good holiday sounds like you needed one! |
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lozza59
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| Teflon-Mike |
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Teflon-Mike
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lozza59
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| Posted: 23:23 - 12 Aug 2011 Post subject: |
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would like your help again please Mike 
i put the engine together thursday and got it running in the bike today (friday) fresh oil and poured a bit over the top of the engine before i hit the button, it did fire up swiftly with no oil leaks and considerably quiter running now, however i have worsened the oil supply issue to the cam.... i run it with the rocker cover off to keep an eye on it and no oil is getting up into the cam bearings.
im just sure i cleaned all the oil ways and the oil pump has come off again but that seems to work ok.
i have been thinking if i have got the metal dowels in the correct places (4 in total right? 2 for each rocker assembly?) would appreciate any info or ideas on how i can find the problem,
and where the locating dowels should be would be helpful.
thanks |
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