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Post by chrisg on Oct 7, 2019 21:21:14 GMT 1
Hi, I have spoken to Grampian motors about a re-bore and they tell me all the older LC's go for the later YPVS pistons. Is this the case or just hype?
Also what kind of clearance should I be asking for? I think they are stockists of Mitaka. I guess original Yam pistons are my first choice, if I can find any.
Note: This type of question is hotly debated on the aircooled site and Im hoping this is not the case here
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Post by dusty350 on Oct 8, 2019 7:33:29 GMT 1
Original Yamaha Lc pistons are NLA, unless you can track down some old stock stashed away somewhere. Mitakas, as long as they are made in Japan and not Taiwan, are absolutely fine. You can use Ypvs Mitakas in an Lc with no problems, but it's wise to cut or file off the tang at the bottom rear edge of the piston skirts to save any potential problems - that will be debated !! Mitaka now produce a specific Lc piston, so just get those to save yourself some work !! Dusty
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Post by dusty350 on Oct 8, 2019 7:36:03 GMT 1
Oh, and a good firm will match the pistons to the bores. Grampians have a very good rep, as do Pjme. Dusty
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Post by midlifecrisisrd on Oct 8, 2019 9:01:08 GMT 1
Oh, and a good firm will match the pistons to the bores. Grampians have a very good rep, as do Pjme. Dusty Mitaka now do lc pistons PJME advertise them Steve
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Post by Tobyjugs on Oct 8, 2019 11:21:38 GMT 1
Normally the piston manufacturers supply the specified cylinder piston tolerance. There should be no debate about that. There is a debate however about removing the middle tang from a YPVS style piston when used in a 4LO engine.
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Post by chrisg on Oct 8, 2019 14:08:19 GMT 1
Normally the piston manufacturers supply the specified cylinder piston tolerance. There should be no debate about that. There is a debate however about removing the middle tang from a YPVS style piston when used in a 4LO engine. Thanks all. There is a debate on the aircooled forum, but there is a consensus that the tang should be removed. Also 1.1/2 thou appears to be the consensus of clearance on AC bikes.
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Post by midlifecrisisrd on Oct 8, 2019 16:10:59 GMT 1
Normally the piston manufacturers supply the specified cylinder piston tolerance. There should be no debate about that. There is a debate however about removing the middle tang from a YPVS style piston when used in a 4LO engine. Thanks all. There is a debate on the aircooled forum, but there is a consensus that the tang should be removed. Also 1.1/2 thou appears to be the consensus of clearance on AC bikes. Clearance will be marked on the boxes. If I remember I'll check a box in the garage Air cooled bikes would run a bigger tolerance I'd think Steve
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Post by chrisg on Oct 8, 2019 22:43:51 GMT 1
My guess is that the LC bike cylinders warm up slower than the piston does, so would need a slightly bigger clearance that the AC bikes,although I may be talking complete ballc**ks
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Post by Deleted on Oct 9, 2019 3:30:34 GMT 1
Heres a conrod after the tang hit the port.
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Post by midlifecrisisrd on Oct 9, 2019 7:57:34 GMT 1
My guess is that the LC bike cylinders warm up slower than the piston does, so would need a slightly bigger clearance that the AC bikes,although I may be talking complete ballc**ks I'd say the liquid cooled had more controlled temperature so the clearance is smaller An aircooled bike on a hot day will have a much higher temperature than an LC It's why you can get more power out an LC. Better heat dispersal 2 people, 2 opinions 🤣 Steve
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Post by beardy on Oct 9, 2019 8:08:21 GMT 1
I read that formula 1 car engines have hot water pumped through them when cold so as to allow the tolerance to grow allowing them to start. This is because the tolerances are so tight when cold they won't turn over.
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Post by chrisg on Oct 9, 2019 18:33:01 GMT 1
I saw a clip from top gear when one of the trio drove a F1 car and as you say it was very nearly seized when cold and had to be warmed up with hot water/oil.
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Post by rigga on Oct 9, 2019 21:14:46 GMT 1
I read that formula 1 car engines have hot water pumped through them when cold so as to allow the tolerance to grow allowing them to start. This is because the tolerances are so tight when cold they won't turn over. Correct, they have heated oil and water passed through, they are I gather practically siezed when cold. Edit beaten by chrisg above
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Post by steven on Oct 9, 2019 23:01:17 GMT 1
Hi, When PJME did my re-bore on my 4L0, six years ago, Paul at PJME phoned me to tell me the barrels were ready. I spoke to Paul for a while on the phone. He said, YPVS piston are what Yamaha recommend for a 4L0 now, and if the piston can coble over that far, that the tang can hit the port, then something else is seriously wrong. He said that he has done loads of 4L0 engines and never removed any tangs and never had a single issue. Paul also said that, in his opinion, removing the tangs is an Urban Myth. I took Pauls advice, and left my tangs intact, as recommended by Yamaha. I dont do a huge amount of miles on mine, but six years down the line, so far so good. Steven.
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Post by dusty350 on Oct 10, 2019 7:16:37 GMT 1
Paul told me exactly the same thing. He had never had a damaged engine come back to him where he had supplied Pv pistons in an Lc engine. I built my engine up, then had input from forum members regards the tangs. To err on the side of caution, I then stripped the top end and removed the tangs - easy job - and slept much easier once I had done it !! There were more than a couple of guys saying the tangs were at fault for their engine damage, so that was enough for me to remove them. You couldn't get the Lc specific pistons at the time, but you can now, so just buy those and save yourself 10 minutes with a hacksaw !! And Paul at PJME is an expert and does this stuff for a living, so he knows what he is talking about, but just a little seed of doubt was enough for me !! Dusty
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Post by rigga on Oct 10, 2019 8:13:52 GMT 1
I've asked this before, and don't recall an answer, the inlet windows on the two types of pistons are different, ypvs being larger .....any impact on performance fitting either style?
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Post by dusty350 on Oct 11, 2019 7:24:34 GMT 1
20181114_195716 by dusty miller, on Flickr Mitaka Lc piston on the left, Mitaka Pv on the right. As you say, a fair difference in hole size. Dusty
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Post by pdxjim on Oct 11, 2019 7:32:21 GMT 1
My tuner(s) say big holes are better (!).
And as much as I like 'tang, I'll be removing them off the ProX 'valve pistons going in my LC build.
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Post by midlifecrisisrd on Oct 11, 2019 8:40:03 GMT 1
Just actually had a think about the tang
1 - the bore would have to be worn oval to get that to catch as the piston would have to not be exactly in line
2 - the lc piston had the exact same bit of metal. It's just cut outs either side so if it's going to hit it will hit
Lights fuse and stands well back 😂
Steve
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Post by reedpete on Oct 11, 2019 10:43:00 GMT 1
I struggle with why there is a debate...
The tang emerged with the brigded inlet of the YPVS motor, doesn’t restrict intake area as its shadowed by the bridge itself.. No such central bridge on the 4L0 so for those applications it’s a redundant feature..in other words no functional benefit from being there... Then there is the question of whether it should be removed .... Well engine builders build engines, clearances all nicely measured and pristine running as quiet as chloroformed church mouse ! Then there are us...mere mortals.... Typically rebores only follow a bore that’s been damaged , but piston failure ( wrong mixture, airleak etc etc ) is much more common. The problem potentially comes when you put a random piston into a bore that is nominally sized correctly.....those of us who understand the importance of correct clearances might check and take action...but most others assume that a replacement piston of ‘the correct size’ is a suitable replacement.
So whereas in an out of spec YPVS engine the tang has absolutely no possibility of causing a problem, the same cannot be guaranteed to be true in a 4L0 and of course no comeback on yamaha or piston supplier is an engine is out of spec....
So pragmatic action has to be to remove as there is no benefit from leaving and a possible benefit, under out of spec conditions, from cutting off.
Of course , the other side of it is the application notes.....one can’t imagine any corporation recommending customers should take a hacksaw to their product in certain applications!
In final summary ...no 4L0 engines in whatever condition have blown up because the tang was removed....same can’t be said the other way around....
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Post by tony2stroke on Oct 11, 2019 11:42:10 GMT 1
I struggle with why there is a debate... The tang emerged with the brigded inlet of the YPVS motor, doesn’t restrict intake area as its shadowed by the bridge itself.. No such central bridge on the 4L0 so for those applications it’s a redundant feature..in other words no functional benefit from being there... Then there is the question of whether it should be removed .... Well engine builders build engines, clearances all nicely measured and pristine running as quiet as chloroformed church mouse ! Then there are us...mere mortals.... Typically rebores only follow a bore that’s been damaged , but piston failure ( wrong mixture, airleak etc etc ) is much more common. The problem potentially comes when you put a random piston into a bore that is nominally sized correctly.....those of us who understand the importance of correct clearances might check and take action...but most others assume that a replacement piston of ‘the correct size’ is a suitable replacement. So whereas in an out of spec YPVS engine the tang has absolutely no possibility of causing a problem, the same cannot be guaranteed to be true in a 4L0 and of course no comeback on yamaha or piston supplier is an engine is out of spec.... So pragmatic action has to be to remove as there is no benefit from leaving and a possible benefit, under out of spec conditions, from cutting off. Of course , the other side of it is the application notes.....one can’t imagine any corporation recommending customers should take a hacksaw to their product in certain applications! In final summary ...no 4L0 engines in whatever condition have blown up because the tang was removed....same can’t be said the other way around.... I just had to get in on this, I have been looking in from time to time and I have to back Peter up on this, there is no advantage in keeping the tang in place, but for the reasons explained above it should be removed, its there because of the bridge in the YPVS engine, but there is no bridge in the 4L1 or 4L0 cylinders, I remember I think it was Tobyjugs that posted pics of his cylinders with the tang just catching on the inlet ports, this was on one of dusty's early engine build threads, you don't need any more proof than that and with the photo of the conrod posted earlier in this thread, why would you take the risk.
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Post by chrisg on Oct 11, 2019 13:19:59 GMT 1
I have seen this bridge in the YPVS cylinders and it does line up with the tang, so I guess that's is job. My personal view is that the tang should go, when in use on a 4L0 without the bridge fitted.
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Post by midlifecrisisrd on Oct 11, 2019 14:14:11 GMT 1
You're not getting my point 🤣
Look at the pic Dusty put up of the 2 pistons beside each other
The bit of metal that is the tang is on both pistons. They are the same length from crown to the skirt/tang
If the tang is going to hit the skirt would too
If anything removing the tang shortens the skirt so will cause more rock
I know sh1t about this by the way. Never owned or built an lc engine
Just mixing it 😜
Steve
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Post by midlifecrisisrd on Oct 11, 2019 14:16:34 GMT 1
I blame the cut outs, not the tang
Being a tangist should be an offence 😆
Steve
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Post by shaunthe2nd on Oct 11, 2019 14:34:46 GMT 1
Reading this and I think I've been tango'd.
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Post by tony2stroke on Oct 11, 2019 19:25:16 GMT 1
I blame the cut outs, not the tang Being a tangist should be an offence 😆 Steve I think your right there, a slight movement at one point in a cylinder can create a larger movement else where, just think about how piston a can move around in the cylinder. It is only the one tang you want to remove, the middle one. Lets face facts here, if the bridge wasn't there then there would be no tang, as 4L0 and 4L1, the bridge is there to stop the piston from wearing as much from the said movement in a port without a bridge, Yamaha say somewhere that the bridge is to allow larger ports and reduce wear on piston due to large port, the cut outs in the piston besides the tangs increases port opening period, the piston needs to be a certain length to help with piston rock and set timing, to increase port timing without massive ports that will cause more piston wear, or too short a piston and risk more piston rock / wear, the best option is is to raise the skirt as Yamaha have done, ie the cut outs and the bridge. I hope this makes sense.
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Post by jon on Oct 11, 2019 20:12:16 GMT 1
Ah the old tang debate again. I agree with reedpete, why the debate?
Now firstly as has been said there are a FEW reports of trouble leaving it, but NONE for removing it.
I think on a fresh bore and standard porting it’s no problem at all.
However why not spend a few minutes removing it just in case?
My take on it is as follows.
The bottom of an LC barrel inlet is curved at the edges. This allows the LC piston to slowly be coersed back into the bore as it tends to rock over the unsupported inlet.
This is not the case with a YPVS piston in an LC barrel. With a lot of wear to the bore, or tuning widening the inlet port; tang can be caught on the bottom of the inlet before it’s coersed back in.
The tang sticking out is also a stress raiser, albeit a small one due to the radii.
I also wonder how much extra heat builds up here due to the friction of a colliding part in bad circumstances? Does this add to the problem?
Jon
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Post by Tobyjugs on Oct 11, 2019 20:42:39 GMT 1
I was going to make a comment but Jon has more or less said it.
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Post by steeley on Oct 12, 2019 5:37:22 GMT 1
Hi, years ago a mate of mine said the LC is making a bit of noise ray could you have a look for me . So i went round took the head and cylinders off and noticed the tangs on the back and thought i take these off on my own builds . So i took the pistons off and pushed one down the cylinder to see if it would catch and it did . I took both tangs off and put a chamfer on the lower edges of the pistons and put it back together . Noise gone. Just to say the engine was fresh as in recon crank and re bore with new pistons with a few hundred miles on it.
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Post by jon on Oct 12, 2019 7:44:15 GMT 1
Hi, years ago a mate of mine said the LC is making a bit of noise ray could you have a look for me . So i went round took the head and cylinders off and noticed the tangs on the back and thought i take these off on my own builds . So i took the pistons off and pushed one down the cylinder to see if it would catch and it did . I took both tangs off and put a chamfer on the lower edges of the pistons and put it back together . Noise gone. Just to say the engine was fresh as in recon crank and re bore with new pistons with a few hundred miles on it. Well there you have it, With some engines failing with the tangs, it could be a red herring. However in this case with only one variable it had to be the tangs. What I was trying to say is it’s more likely to fail on a worn/badly machined bore. Jon
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