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Post by headcoats on Jul 17, 2024 18:00:10 GMT 1
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Post by Mr Kipling on Jul 17, 2024 18:09:45 GMT 1
There on their last legs that,s for sure....
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Post by Tobyjugs on Jul 17, 2024 20:51:17 GMT 1
I've got a couple of worn sets at +2.50 mm. All old race spares i bought from a retired racer.
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Post by muttsnuts on Jul 17, 2024 21:12:49 GMT 1
overheating issues highly likely, that's what normally happenes with them, 2mm is the maximum I recommend
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Post by Tobyjugs on Jul 18, 2024 0:05:26 GMT 1
overheating issues highly likely, that's what normally happenes with them, 2mm is the maximum I recommend Hmm food for thought Dave. Would that be for normal turn key clients? Not sure of the Ron Fahron 375 size pistons. Lots of coolheads out there that divert more cooling water over the cylinder heads. Yesterday i got home and was looking at my 400 and the exhaust looked hot but a bit further down the pipe than usual. Its using re-sleeved YPVS cylinders. Its at present using 68,25 mm pistons (+4.25 mm   ) and i am thinking about 68.50 mm pistons. I need to check if it's possible to further modify the modified standard cylinder head it's using. At the moment it won't pull granny off the piss pot and barely wheelies in 2nd gear. It does start easy with a bit of choke. |
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Post by urbantangleweed on Jul 18, 2024 8:48:16 GMT 1
Is 66.5mm within the scope of standard valves or will they need to have also been machined at the time of rebore?
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Post by midlifecrisisrd on Jul 18, 2024 8:53:31 GMT 1
I thought the overheat problem on large bore was down to 2 issues
1) the liner is that thin that it doesn't dissipate heat as well
2) if the bore/liner is slightly off then there are thin and thinner sections that cause hot spots
I would also think that on a ypvs the liner at the pv would be very weak
I'd previously heard of one type of barrel taking 2mm max and the other 2.5 but I had 1ua was allowed bigger in my head but may just be old and confused 😕
Steve
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Post by midlifecrisisrd on Jul 18, 2024 8:54:21 GMT 1
Is 66.5mm within the scope of standard valves or will they need to have also been machined at the time of rebore? I'd think they would need trimmed a little. Steve |
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Post by headcoats on Jul 18, 2024 9:06:06 GMT 1
I had some bored to 1.75 by PJ'S and they trimmed the valves at that size and advised to open up head gasket too.
I sold them on so didn't check what the head gasket needed to fit
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Post by Tobyjugs on Jul 18, 2024 9:12:31 GMT 1
The Valves in my engine are pinned open.
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Post by Norbo on Jul 18, 2024 9:34:50 GMT 1
Thats big. The liner gets thin on a ypvs and the pistons get to close to the valves may even have to mod them at this size to be on the safe side .
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Post by chrisg on Jul 18, 2024 16:54:09 GMT 1
If you look at pic 4, that shows just how thin the liner is. Ive seen worse that have been at 2mm os but been bored off centre.
At £500, walk away.
These cylinders are not like the 4L0 and are more readily available.
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) and i am thinking about 68.50 mm pistons. I need to check if it's possible to further modify the modified standard cylinder head it's using. At the moment it won't pull granny off the piss pot and barely wheelies in 2nd gear. It does start easy with a bit of choke.
