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350 powervalve fun! - Update: Its getting less fun...

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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 12:59 - 15 Jan 2009    Post subject: 350 powervalve fun! - Update: Its getting less fun... Reply with quote
Hello fellow two stroke beardy people!

I've taken the head and barrels off of my 350 powervalve at the weekend. I've got photos so I'll update my show and tell thread at some point. But I have a question...

I didn't take the head and barrels off to do a top end rebuild. I did a compression test, and its bang on the money. No, I took the barrels off to access the powervalves. Some feckin eejit swapped the powervalves between barrels. When that didn't appear to work they simply removed the powervalve pulley and put a bit of threaded bar all the way through with a couple of nuts and washers to hold it all together... crazy.

Anyway, I digress. I've got a good set of powervalves from a chap on the RD discussion group, so thats all good I can get them working. My question is... while I've got the head and barrels off... is it worth me doing the piston rings? As I said earlier I've got good compression, the barrels look beautiful with no scoring and the pistons are good. The rings look a little worn... is this a job I should do while the top end is in bits?

Cheers!
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

Last edited by MarJay on 18:00 - 18 Jan 2009; edited 1 time in total
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Fadel
Trackday Trickster



Joined: 06 Feb 2006
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PostPosted: 13:04 - 15 Jan 2009    Post subject: Reply with quote
I would if it was me, false economy not to really while it's all apart, even if it was just for peace of mind that they were new etc.
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MarJay
But it's British!



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PostPosted: 15:13 - 15 Jan 2009    Post subject: Reply with quote
BLUEX5 wrote:
If your in there anyway do small ends and rings, for the price of them it doesn't hurt and keeps the motor nice and fresh.


Right so you reckon small end bearings too? cool. Thats just what I wanted to know! Smile
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MarJay
But it's British!



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PostPosted: 17:05 - 15 Jan 2009    Post subject: Reply with quote
BLUEX5 wrote:
Small ends are about £6 a piece, and you'll need a couple of gudgeon pin clips too. I always do them if I have the top end off on mine, keeps the top end quiet.


Now for the really hard stuff... what should I do to run in the new rings and bearings?
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Howling TerrorOutOfOffice
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PostPosted: 18:12 - 15 Jan 2009    Post subject: Reply with quote
Hi, i have a friend who's a RD junkie, he recommends a run in period of 600 miles. Don't enter the powerband if you can help it, use your gears so no over labouring up hills etc
He said its a pig of a job but its far far worse having to do a rebore which he says 1000 miles !


Pat
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Blue_SV650S
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Joined: 27 Nov 2008
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PostPosted: 18:24 - 15 Jan 2009    Post subject: Reply with quote
MarJay wrote:
BLUEX5 wrote:
Small ends are about £6 a piece, and you'll need a couple of gudgeon pin clips too. I always do them if I have the top end off on mine, keeps the top end quiet.


Now for the really hard stuff... what should I do to run in the new rings and bearings?


I'd be tempted to put some new rings in there to increase time before it next goes pop ...

But you do need to consider one thing ...

When an engine is made/rebored, the barrel is 'honed' isn't it ... the purpose of this 'honing' is to allow the bore and rings to 'seat' properly. If you put new rings in a bore that hasn't been re-honed, it won't have this initial seating ...

As such you are likely to have slightly less compression/power as the rings wont shape themselves to the bore properly...

I think having fresh rings is more important though Wink

If you do go for new rings, consider scuffing the bores up a bit with emery cloth (rotatory cross hatched - not up and down) ...
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 20:03 - 15 Jan 2009    Post subject: Reply with quote
Blue_SV650S wrote:
If you do go for new rings, consider scuffing the bores up a bit with emery cloth (rotatory cross hatched - not up and down) ...


That sounds a bit scary... BlueX5 didn't mention it and he's a 2 stroke Guuu ruuu.

Aren't you the anti two stroke man anyway?... no offense! Smile
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
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Blue_SV650S
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PostPosted: 21:11 - 15 Jan 2009    Post subject: Reply with quote
MarJay wrote:

That sounds a bit scary... BlueX5 didn't mention it and he's a 2 stroke Guuu ruuu.

Aren't you the anti two stroke man anyway?... no offense! Smile


To my mind a 2-stroke is a bit like really feisty women ...

Make for an interesting ride, but impossible/high maintenance to live with and oh so very fickle!! Wink

As a long term-er, I'd rather have a highly tuned 4-stroke ... can be a bit feisty if you twist the tube just right, but much easier/better to live with!! Thumbs Up

Oh and the honing is there for for exactly the same reason in 4-strokes too ... its not just 2-strokes that require the rings seating ....

Interestingly there is quite an argument for trashing a freshly rebuilt (and honed) engine from the off (once it is hot) as it seat the rings better ...
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Last edited by Blue_SV650S on 21:31 - 15 Jan 2009; edited 1 time in total
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MarJay
But it's British!



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PostPosted: 22:24 - 15 Jan 2009    Post subject: Reply with quote
Blue_SV650S wrote:

Make for an interesting ride, but impossible/high maintenance to live with and oh so very fickle!! Wink


Ah yes, but which would you rather have for the odd ride? Fit supermodel prone to throw crockery, or frumpy librarian? Wink
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
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stevo as b4
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Joined: 17 Jul 2003
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PostPosted: 22:45 - 15 Jan 2009    Post subject: Reply with quote
Id definately get a hone that would fit in a decent electric drill to give the bores a bit of a key before you fit the new rings. TBH if you don't do engine work that often then it's probably cheaper to take the barrels round to a bike shop and get them to run a hone through them for you. My local shop did my Speedfight barrel for nothing!

Also when you fit the new rings, just check the ring gaps and also if there is any wear in the ring grooves in the pistons. You might have to use a feeler gauge to check this. I have been burnt before by fitting new rings to a worn piston that had too much slack in the ring lands. I like to always fit a new piston and rings together now as a set. Even if i just hone the bore and fit new std size pistons and rings to a part worn engine.
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 23:13 - 15 Jan 2009    Post subject: Reply with quote
stevo as b4 wrote:
Id definately get a hone that would fit in a decent electric drill to give the bores a bit of a key before you fit the new rings. TBH if you don't do engine work that often then it's probably cheaper to take the barrels round to a bike shop and get them to run a hone through them for you. My local shop did my Speedfight barrel for nothing!

Also when you fit the new rings, just check the ring gaps and also if there is any wear in the ring grooves in the pistons. You might have to use a feeler gauge to check this. I have been burnt before by fitting new rings to a worn piston that had too much slack in the ring lands. I like to always fit a new piston and rings together now as a set. Even if i just hone the bore and fit new std size pistons and rings to a part worn engine.


Well I checked the ring gaps on the rings that are in there, and its absolutely OK. I wouldn't be surprised if the pistons were quite new.

Thats not to say that the new rings will be OK of course though. Hmm. This is getting more complicated than I thought it would be. Still, its fun.

I've ordered a hone that fits on an electric drill, its a Draper one and cost £12 delivered.
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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MarJay
But it's British!



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PostPosted: 01:28 - 16 Jan 2009    Post subject: Reply with quote
I've just read on a US two stroke website that I shouldn't use a spring loaded hone on a two stroke bore as it will snag on the ports...

D'oh
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Robby
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Joined: 16 May 2002
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PostPosted: 13:10 - 16 Jan 2009    Post subject: Reply with quote
Stop being such an old woman Marje.

The engine is design is 30 years old and it isn't pushing 1000bhp/litre. You have some room for error.

If you think the pistons are ok, then put it back together with rings and little ends. If as a consequence you need to reopen the motor to do pistons, rings, little ends and gudgeon pins in 4000 miles, so be it. It'll take you a while to do 4k on that bike, and you love opening the engine up.

You bought the tool, so run a quick hone over it. In motorcycle mechanics magazine they recommend diesel as a lubricant when running a glaze buster/honing tool, because it offers some lubrication and also washes away anything you scrape off the side of the bore.

And don't go overboard. You're giving it a very quick hone, not trying to rebore it with the wrong tool.
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MarJay
But it's British!



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PostPosted: 13:42 - 16 Jan 2009    Post subject: Reply with quote
Well I've ordered a re-usable copper head gasket from the states. Its slightly thinner than a stocker, and with the head skim should give me the right squish gap. Apparently I've got to anneal it before I fit it, which should be great fun too.

I've also bought some 83mm centre to centre front brake calipers that will fit on the bike as the standard RD 2 potters are crap. They might be a little bit of overkill though as they are 4 pot Nissins from a TT600... Embarassed not bad for £30 though. There is a guy on the RD forum with them on his bike and they work... quite well shall we say?

As well as the engine rebuild, I also need to drain, clean and seal the fuel tank, remove the wheels and possibly get them powder coated, get new tyres, re fit the wheels, rebuild the front brake master cylinder, fit the calipers and then it should be vaguely ready for an MOT once its all back together. I might also have to find some suitable fork gaiters, because the brand new fork seals are weeping a bit ( I fitted new top and bottom bushes too so I think the fork leg might be pitted or something).

Then I can concentrate on the rear end and seeing if I need stuff like suspension bushes and possibly a new rear shock. I might need to buy a grease gun so I can make use of my grease nipple! Embarassed Smile

As I said, I'm taking photos as I go and am going to do a big write up at the end I think. I can't be bothered to keep updating an old thread.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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Blue_SV650S
World Chat Champion



Joined: 27 Nov 2008
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PostPosted: 14:12 - 16 Jan 2009    Post subject: Reply with quote
MarJay wrote:
Well I've ordered a re-usable copper head gasket from the states. Its slightly thinner than a stocker, and with the head skim should give me the right squish gap.


Shocked I can see 2 causes of pre-ignition right there Wink .. its gonna give you the WRONG* squish!!

Are you gonna run it on super unleaded or retard the timing?

*i.e. wrong that it is not standard squish, right if you are trying to build a higher compression engine Wink
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MarJay
But it's British!



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PostPosted: 15:37 - 16 Jan 2009    Post subject: Reply with quote
Blue_SV650S wrote:
MarJay wrote:
Well I've ordered a re-usable copper head gasket from the states. Its slightly thinner than a stocker, and with the head skim should give me the right squish gap.


Shocked I can see 2 causes of pre-ignition right there Wink .. its gonna give you the WRONG* squish!!

Are you gonna run it on super unleaded or retard the timing?

*i.e. wrong that it is not standard squish, right if you are trying to build a higher compression engine Wink


Currently the squish is 1.9mm. I'm aiming for 0.9mm - and it won't increase the compression too much. 0.8mm is the smallest you can go on standard octane fuel. 0.75mm is the smallest squish gap you can run. So I should be well within tolerances.

John Penfold on 'The Elsie Cult' wrote:
Reducing the squish gap also reduces the compressed volume, which increases compression. This actually optimises the compression ratio for the stock YPVS because Yamaha have left a good bit of slack here, too. There are two types of cylinder head on the YPVS models, marked Y1 and Y2. They are clearly marked on the top. The Y2 is the higher-compression head. With a squish gap of 1.9 mm even the 'high compression' Y2 head gives a lowly compression ratio of 6.0:1 (measured from the top of the exhaust port). With a squish gap of 0.9mm the compression ratio rises to 7.1:1, which is actually a pretty good ratio for road use with ordinary petrol. As a rule of thumb, you can push the compression ratio to perhaps 7.7:1 on this engine with ordinary petrol, and retarded ignition, before detonation happens. However, 7.7:1 is not a hard and fast rule, and 7.5:1 is probably a better safe maximum.

The increase in compression can get a bit hairy when the engine has been overbored, which increases the compression ratio. For instance, with a 1 mm overbore and taking the squish gap right down to 0.75 mm, the compression ratio will rise to 7.5:1, which some would consider to be right on the limit for use with normal petrol. If you fall into this area, you might want to consider raising the exhaust port to 26mm from the stock 27.5 mm purely to lower the compression, rather than for other performance considerations. That would lower the compression from 7.5:1 to 7.2:1 in the above examnple, back into the safe area.


Info here:https://homepage.eircom.net/~johnpenfold/elsie/worksheet1.html
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 15:55 - 16 Jan 2009    Post subject: Reply with quote
I'm wondering if I ought to do the pistons and pins as well...
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Blue_SV650S
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PostPosted: 16:54 - 16 Jan 2009    Post subject: Reply with quote
MarJay wrote:
I'm wondering if I ought to do the pistons and pins as well...


Didn't realise there was that much 'slack' with the compression ... but then i guess as it is for a world market, it must be set for like 88ron or summin?

How much are a set of pistons?

Do you have any idea how many miles the old set have done?
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MarJay
But it's British!



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PostPosted: 17:07 - 16 Jan 2009    Post subject: Reply with quote
Blue_SV650S wrote:
How much are a set of pistons?

Do you have any idea how many miles the old set have done?


Trying to find that out... no idea how many miles the old pistons have done.

If I do get the squish gap a little wrong then I can always run it on stupid unleaded anyway. Tescos do a good line of 99 octane that I use in my car. It would be no hassle to fill up a Jerry can when I fuel the car. This bike is NOT going to be transport, so it doesn't really matter if I can't use 95 octane fuel.
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Blue_SV650S
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PostPosted: 17:10 - 16 Jan 2009    Post subject: Reply with quote
MarJay wrote:
Blue_SV650S wrote:
How much are a set of pistons?

Do you have any idea how many miles the old set have done?


Trying to find that out... no idea how many miles the old pistons have done.

If I do get the squish gap a little wrong then I can always run it on stupid unleaded anyway. Tescos do a good line of 99 octane that I use in my car. It would be no hassle to fill up a Jerry can when I fuel the car. This bike is NOT going to be transport, so it doesn't really matter if I can't use 95 octane fuel.


Just put new pistons in ... for the sake of what £80? it'll put your mind at rest ... that and if it went pop on you (and you hadn't replaced the pistons) its gonna cost you a lot more and you will kick yourself!! Wink
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