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Post by JonW on Dec 21, 2014 0:19:05 GMT 1
Anyone ever measured a set of new OEM bushes and PVs? Im happy to take a measurement off more than one person for each part as i expect the manufacturing tolerances vary as well. Im assuming the tolerances are pretty wide for these parts anyway as the seals do the sealing and the bush is plain and with one part being alloy and the other bronze, they will heat up in use and fill the gaps a bit too... Anyway, would love to hear a measurement if you have any of these parts brand new as I have a mate who will fix my not so great sets for me with custom parts  |
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Post by lb on Dec 21, 2014 2:11:25 GMT 1
Jon im also curious as to the materials used. Maybe one of the engineering types could shed some light,brass or oil sintered bronze?
Now to the sizes,oem 350cc pv & bush.
Bush o/d is 35mm,i/d is 17.20mm.
Pv shaft is 16.80mm
So 0.40mm clearance.
New bush bearing material looks to be sintered bronze too.
Just for comparison,i measured up a 250 pv asd well.
Bush o/d is 32.00mm.!!!
I/d is 17.20mm too...
Why Yamaha would make the bush o/d sizes different between the 250 & 350 is beyond me. Like 3mm is not going to change anything apart from market sales?
The 350 pv n bush i measured are brand new the 250 pv n bush are bout 15k km old. Measured with dial caliper 0.05mm.
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Post by JonW on Dec 21, 2014 2:22:40 GMT 1
Great info Jason, anyone else got a set to measure, were they all the same?
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Post by Deleted on Dec 21, 2014 3:45:03 GMT 1
I wish you'd asked that question about 3 months ago, before I put the engine together
Now I'm going to have to pull it apart again to measure the newies I got
Bugger
Having said that here are measurements of the old ones that have only 24000kms on them if that helps
35mm od on the bush, smallest id (ie on the bronze internal bush) 17.25mm larger ID 23mm
Powervalve OD 17.2mm
Clearance 0.05mm, there is no discernible play from the bush on the valve
So slightly different to lb
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Post by markhoopy on Dec 21, 2014 11:11:25 GMT 1
Just sold a new pair of Yam p/vs to northernmonkey - he got them three days ago so you could pm him and ask if he can get measurements too .. rdlccrazy.proboards.com/user/2989 |
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Post by JonW on Dec 21, 2014 22:34:09 GMT 1
Glyn tells me 'It's .14-.18mm that was/is the factory spec' so no need to measure guys, but thanks for the input!
So, anyone know about the material as Jason asked?
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Post by steeley on Dec 22, 2014 7:58:21 GMT 1
I cant tell you what the material is only that the engineer that did some work on mine said it was not very good.so it seems to me a better spec material is surely the way to go and sleeve the bearing surfaces on the power valves.
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Post by slinger on Dec 22, 2014 14:38:39 GMT 1
Glyn tells me 'It's .14-.18mm that was/is the factory spec' so no need to measure guys, but thanks for the input! So, anyone know about the material as Jason asked? The power valve is a aluminium silicon alloy and is really quite soft, the wear we tend to see is not from rotation but the shake rattle and roll the valves experience in there life time. When I serviced a set of valves I would turn the bearing shift concentric to each other and to a nominal size, the bush I used brass and pressed the old one out then pressed the new one it. Looking back at the question I asked about the valve manufacturing clearance has got me thinking after reading Jasons post after he measured a set of new valves Was the info supplied....... manufacturing tolerances or running clearance's, either way I machined mine to .14/.18mm bearing clearace and never had any problems. |
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Post by JonW on Dec 22, 2014 22:28:42 GMT 1
Thanks again mate, much appreciated!
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Post by lb on Dec 23, 2014 1:13:02 GMT 1
Thank you very much Glyn,just what i needed to hear. Brass is cheaper & will go with your clearances too.
This might help out alot of the 250 lads over here as ive never seen new 250 pv's or bushes advertised....
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Post by frosti on Jan 9, 2015 15:23:13 GMT 1
I am planning on having my Powervalves anodized (would like them in red,,;-) )because its a lot cheaper just changing the bushes instead of Everything. And those PV`s are expensive,,  |
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Post by slinger on Jan 10, 2015 3:41:42 GMT 1
I am planning on having my Powervalves anodized (would like them in red,,;-) )because its a lot cheaper just changing the bushes instead of Everything. And those PV`s are expensive,, Anodizing them won't help at all, the sub material is still soft. Machining them to what would be consider the correct tolerance will/does stop the valves wearing out so quick. Maybe just something else Yamaha got wrong from the get-go |
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Post by lb on Jan 10, 2015 7:35:46 GMT 1
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Post by frosti on Jan 10, 2015 12:24:40 GMT 1
I am planning on having my Powervalves anodized (would like them in red,,;-) )because its a lot cheaper just changing the bushes instead of Everything. And those PV`s are expensive,, Anodizing them won't help at all, the sub material is still soft. Machining them to what would be consider the correct tolerance will/does stop the valves wearing out so quick. Maybe just something else Yamaha got wrong from the get-go The surface of the valves would be a lot harder than the bushings, therefore the bushings will be the ones wearing out, i believe. Just my 2 cents. 
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Post by bare on Jan 12, 2015 4:06:19 GMT 1
I asked the '2stroke shop ' w**ker/ Bozo that exact question.
He wasn't happy I asked either IRRC.
MY just received Bespoke billet Valves had Stupid clearances on my Brand New OEm Yama bushes. Each one different!
Effing Fool claimed that was how they were supposed to be.. Bollocks!
I had MY 'billet' valves Fitted with steel sleeves heat shrunk onto the valves and precision matched to my New oem bushes by a friend/local.. Proven competent.. racer/ machinist.
Frankly I don't recall the running clearances fitted.
Actually I don't remember asking :-) as some people consider asking on their work as a slur on their competence /integrity.
All I know is they then fit 'perfectly' and have worked Sans issue for several seasons since.
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Post by JonW on Jan 12, 2015 4:59:51 GMT 1
LOL, Well I wobbled my TSS billet PVs in the TSS holders/bushes and they passed my 'feels ok?' test so i fitted em in my cyls on my F1, but these days im a little more scientific about this stuff, like many of us I guess :/
Im hoping to get my mate to fit some steel sleeves to some of my knackered OEM PVs and size new insert bushes to fit.
The other thing we've noticed is that the cylinders are pretty badly marked where the holders fit. I could have these bored and new holders made, but could I instead have a 2nd grove turned into the holders and just run a 2nd set of O rings to be sure of a decent seal? Anyone tried this? Seems easier than grinding meat off my cyls and creating a new holder for each cylinder...
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Post by midlifecrisisrd on Jan 12, 2015 9:04:42 GMT 1
Common over here to have the barrel machined and a thin insert to bring back to standard.
More typically we cover the bush inot silicone before fitting.
Won't move after that
Steve
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Post by JonW on Jan 12, 2015 9:53:57 GMT 1
My issue with High temp silicone is that its a bugger to get out and i thought the double o ring might be a more elegant solution :/
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Post by muttsnuts on Jan 12, 2015 21:52:54 GMT 1
Funny this, I've just measured up some today, got some new ones and measured them as I am going to be making some new inserts to replace the worn ones on a few sets I have, I am going make them out of oilite bearing material (self lubricrating sintered bronze), much harder than brass and the original Yamaha stuff, but self lubricates so shouldn't cause too much wear on the PV itself. I am going to be using 0.14 to 0.18mm clearance as mentioned previously as that is what the spec should be
HTH
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Post by JonW on Jan 12, 2015 22:48:13 GMT 1
Ta Mutts, its good more of us are working on these and improving them i think, all info is good |
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Post by jon on Jan 12, 2015 23:50:45 GMT 1
I don't think Yamaha got it too wrong to start with.
After all they have put together a concept through to production with the YPVS.
There are always tolerances during production, and some combinations will be better/longer lasting than others.
How many original YPVS engines failed after few miles? Very few I expect.
There is also the real need to produce a bike at a realistic price, so materials and machining was considered.
These days we (on this forum, amongst others) want to try and build as good as, if not better than the original. That means spending money on better materials and newer processes / technologies.
However let's not forget, the powervalves have an extremely hard life due to movement, heat and oil, the softer part is always going to fail first.
If you make the valves harder the bushes will fail first.
I personally think every case is different, and if the solution is proposed by a person with hands on realisation of the problem, solving abilities and mechanical ability (in this case) it will probably work.
JonW, I love your idea of a second o-ring, but can't comment as I have not seen your barrels. Sounds viable though. As does oversize o-rings, tapered bushings etc.
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