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REBORE
Nov 22, 2019 2:26:47 GMT 1
Post by norman68 on Nov 22, 2019 2:26:47 GMT 1
just had ypvs barrels rebored out to 1.25 oversized, the machine shop supplied the pistons , when i got the barrels back they had done a good job but the pistons dont look right, rear skirt on piston is flat with no cut outs and the ports look very round as opposed to squarish any one any ideas or am i being fussy
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REBORE
Nov 22, 2019 2:28:50 GMT 1
Post by JonW on Nov 22, 2019 2:28:50 GMT 1
pix?
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REBORE
Nov 22, 2019 6:57:12 GMT 1
Post by norman68 on Nov 22, 2019 6:57:12 GMT 1
at work for the next 2 weeks but have been trawling the net and they look very much like 350lc pistons will try and upload some photos
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Post by dusty350 on Nov 22, 2019 7:16:58 GMT 1
Sounds like you have Lc pistons maybe ? Lc piston on the left, Pv piston on the right, both Japanese Mitaka's 20181114_195716 by dusty miller, on Flickr Dusty
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REBORE
Nov 22, 2019 9:43:23 GMT 1
via mobile
Post by norman68 on Nov 22, 2019 9:43:23 GMT 1
Deffo lc piston that's what the machine shop sent back with the barrels
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REBORE
Nov 22, 2019 23:05:56 GMT 1
Post by 4l04ever on Nov 22, 2019 23:05:56 GMT 1
I would get back in touch and ask them to change the pistons for YPVS ones. The windows will affect performance as smaller than YPVS windows.
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REBORE
Nov 23, 2019 0:45:27 GMT 1
Post by reedpete on Nov 23, 2019 0:45:27 GMT 1
But if they’ve bored to suit one set of pistons then clearances are very unlikely to be right if you just random pick another set.....
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REBORE
Nov 26, 2019 20:22:42 GMT 1
Post by norman68 on Nov 26, 2019 20:22:42 GMT 1
phoned company that rebored barrels and told them it was lc not ypvs pistons that they supplied, he told me grampian supplied the pistons and they were the right ones , i told him again they were lc pistons not ypvs again he said grampian said lc pistons work in a ypvs but ypvs pistons dont work in an lc
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REBORE
Nov 26, 2019 20:37:18 GMT 1
Post by reedpete on Nov 26, 2019 20:37:18 GMT 1
phoned company that rebored barrels and told them it was lc not ypvs pistons that they supplied, he told me grampian supplied the pistons and they were the right ones , i told him again they were lc pistons not ypvs again he said grampian said lc pistons work in a ypvs but ypvs pistons dont work in an lc ‘Work’ agree, but not correct, and obviously with reduced open time area! As for the second part of the quote, that will set the tang debate alight !
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REBORE
Nov 26, 2019 20:38:18 GMT 1
via mobile
Post by midlifecrisisrd on Nov 26, 2019 20:38:18 GMT 1
phoned company that rebored barrels and told them it was lc not ypvs pistons that they supplied, he told me grampian supplied the pistons and they were the right ones , i told him again they were lc pistons not ypvs again he said grampian said lc pistons work in a ypvs but ypvs pistons dont work in an lc That's funny cause the lc mitaka pistons are a recent thing Grampians supplied YPVS pistons up to that point so was the norm Steve
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REBORE
Nov 26, 2019 21:51:00 GMT 1
via mobile
Post by Deleted on Nov 26, 2019 21:51:00 GMT 1
phoned company that rebored barrels and told them it was lc not ypvs pistons that they supplied, he told me grampian supplied the pistons and they were the right ones , i told him again they were lc pistons not ypvs again he said grampian said lc pistons work in a ypvs but ypvs pistons dont work in an lc Got YPVS pistons in my LC and they work a treat, so a bit of questionable advice there.
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Post by pdxjim on Nov 27, 2019 5:02:46 GMT 1
phoned company that rebored barrels and told them it was lc not ypvs pistons that they supplied, he told me grampian supplied the pistons and they were the right ones , i told him again they were lc pistons not ypvs again he said grampian said lc pistons work in a ypvs but ypvs pistons dont work in an lc He's got that backwards. 'Valve pistons work well in LC and AC, but not the other way 'round.
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REBORE
Nov 27, 2019 8:51:38 GMT 1
via mobile
Post by Tobyjugs on Nov 27, 2019 8:51:38 GMT 1
Interesting thread, I think the difference is 2 or 3 pk.
I've used pistons with no holes in a YPVS engine and with holes. I will try to post the results later tonight.
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Post by headcoats on Nov 27, 2019 9:14:39 GMT 1
At the end of the day you want the correct Pistons for your barrels
It's how they will handle this will be interesting
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Post by Tobyjugs on Nov 27, 2019 10:20:06 GMT 1
At the end of the day you want the correct Pistons for your barrels It's how they will handle this will be interesting Definately thats what you pay a professional for.
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REBORE
Nov 27, 2019 11:22:46 GMT 1
Post by headcoats on Nov 27, 2019 11:22:46 GMT 1
Has the reborer not explained to grampians that it was YPVS piston he needed as Grampian have a long history of this work ?
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REBORE
Nov 27, 2019 15:07:14 GMT 1
Post by steve h on Nov 27, 2019 15:07:14 GMT 1
phoned company that rebored barrels and told them it was lc not ypvs pistons that they supplied, he told me grampian supplied the pistons and they were the right ones , i told him again they were lc pistons not ypvs again he said grampian said lc pistons work in a ypvs but ypvs pistons dont work in an lc He's got that backwards. 'Valve pistons work well in LC and AC, but not the other way 'round. That explanation to you is very much an arse covering exercise hoping that you will go away. They are the wrong pistons. Mr Yamaha san design team made them different for a reason... not because they had nowt to do that week. A bollock has been dropped.. simple.
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REBORE
Nov 27, 2019 15:12:14 GMT 1
Post by chippy348 on Nov 27, 2019 15:12:14 GMT 1
phoned company that rebored barrels and told them it was lc not ypvs pistons that they supplied, he told me grampian supplied the pistons and they were the right ones , i told him again they were lc pistons not ypvs again he said grampian said lc pistons work in a ypvs but ypvs pistons dont work in an lc The company should know the difference if they are doing this type of work ? Typical reply from Grampians TBH, while the LC piston will work in a YPVS they are not the correct type. Grampians have a saying " it will do a turn" comes from the days when people were using these bikes for a mode of transport rather than there pride and joy of today. They have the correct YPVS pistons in stock so your machine shop can get them swapped, just get him to measure them as they have known to be different sizes. I hope you get it sorted
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REBORE
Nov 28, 2019 7:58:14 GMT 1
Post by JonW on Nov 28, 2019 7:58:14 GMT 1
Go back and stand there in front of the manager. If that doesnt work speak to Grampians about it. Its not acceptable like this. You cant just run any old piston in any cylinder, it needs to be correct. End of.
IMHO companies that dont hold their hands up and say 'sorry we were wrong, we'll sort it' and then get it done should be named and shamed and then avoided alike the plague.
At this point I'm also avoiding Grampians if they sent the wrong pistons knowing what it was for. What they supplied is just plan wrong. Just cos it fits doesnt mean its right.
If either company is reading this then they need to sort it out. Sure, they might lose money on this job but customer service is king. Sort it out you w#*#ers!
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REBORE
Nov 28, 2019 8:11:25 GMT 1
Post by stusco on Nov 28, 2019 8:11:25 GMT 1
I have a question about buying a piston when you don’t need a rebore, how do you get the right piston if there is a difference in size due to quality control?
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REBORE
Nov 28, 2019 9:13:43 GMT 1
via mobile
Post by midlifecrisisrd on Nov 28, 2019 9:13:43 GMT 1
I have a question about buying a piston when you don’t need a rebore, how do you get the right piston if there is a difference in size due to quality control? My take is that the piston variation is very small and more crucial with a new bore to get it "exact" In real life back in the day if your bike seized under warranty they would throw new cylinders and pistons in it without checking Probably why you got fast and slow ones. Once the bore has been run in the variance in piston size is most likely negligible Steve
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REBORE
Nov 28, 2019 10:26:20 GMT 1
Post by Deleted on Nov 28, 2019 10:26:20 GMT 1
I always thought the pistons main job was to give the correct rings somewhere to go.
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REBORE
Nov 28, 2019 10:32:14 GMT 1
via mobile
Post by Tobyjugs on Nov 28, 2019 10:32:14 GMT 1
Interesting thread, I think the difference is 2 or 3 pk. I've used pistons with no holes in a YPVS engine and with holes. I will try to post the results later tonight. Internet was poor last night. I just want to say get the correct pistons and measure the clearance between piston and bore. If this is good problem solved. Remember there is a tolerance for this as well. With today's manufacturing processes I think the correct pistons will fit. I also think if you rode your bike with the above pistons fitted and then the correct pistons fitted you will not notice any difference.
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REBORE
Nov 28, 2019 11:12:21 GMT 1
Post by JonW on Nov 28, 2019 11:12:21 GMT 1
I agree. My reborer has said often that all tis boring to piston size is 1950s technology. These days pistons are made properly and to size for the bore you want, ie +0.25 etc.
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REBORE
Nov 28, 2019 13:42:31 GMT 1
Post by Norbo on Nov 28, 2019 13:42:31 GMT 1
phoned company that rebored barrels and told them it was lc not ypvs pistons that they supplied, he told me grampian supplied the pistons and they were the right ones , i told him again they were lc pistons not ypvs again he said grampian said lc pistons work in a ypvs but ypvs pistons dont work in an lc Ypvs ones do work in an lc a few years back that was all you could get you just need to grind of the center tab. LC ones will fit and work in your ypvs as well . However they have smaller holls and you will loos power not a lot but it will run better with ypvs ones fitted .
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Post by stusco on Nov 28, 2019 15:22:08 GMT 1
I got my lc rebored by pjm and the pistons weren’t matched I measured them and the barrels both were in spec the pistons were in sealed boxes so I don’t think it matters as long as the rebore is correct
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REBORE
Nov 28, 2019 19:59:46 GMT 1
Post by roach3 on Nov 28, 2019 19:59:46 GMT 1
After i removed the top end to put new powervalves in i noticed one of the pistons had a small piece break away from the crown i immediatly thought rebore and new pistons i measured the bores and they were 0.75 i sent the barrels away with instructions to rebore and supply pistons etc got a call to say barrels are fine and just need pistons so ive purchased a set of 0.75 mitaka kits and fitted them. they seem a good fit and spin over ok soon find out if they are alright when i fire it up.
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REBORE
Nov 28, 2019 21:33:37 GMT 1
Post by oldelsieboy on Nov 28, 2019 21:33:37 GMT 1
I got my lc rebored by pjm and the pistons weren’t matched I measured them and the barrels both were in spec the pistons were in sealed boxes so I don’t think it matters as long as the rebore is correct That's unusual, all the pistons I've had supplied by PJME with rebored barrels have been matched to the bores & marked R/H & L/H OEB
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REBORE
Nov 28, 2019 21:50:12 GMT 1
Post by stusco on Nov 28, 2019 21:50:12 GMT 1
Mark Dent did my RG using Grampian I believe they were matched but Mick Abbey did my lc the first time they weren’t matched
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REBORE
Nov 30, 2019 2:13:45 GMT 1
Post by reedpete on Nov 30, 2019 2:13:45 GMT 1
What do you mean ‘not matched’ ?
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