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Post by jon on Oct 19, 2021 22:01:38 GMT 1
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Post by midlifecrisisrd on Oct 19, 2021 22:33:29 GMT 1
I maybe wrongly was under the impression the LC went up to 1mm
YPVS was only 0.5
But LC ain't my strongest subject
Steve
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Post by arrow on Oct 19, 2021 22:38:12 GMT 1
Thats odd. The air cooled bikes went up in 0.25mm increments, but I was pretty sure the lc went up at 0.5mm increments. And only to 1mm oversize with Art (genuine) pistons.
Correction; lc parts book shows just two over sizes. 0.25mm and 0.5mm.
The part number on those rings on ebay does follow the logical sequence though.
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Post by Norbo on Oct 20, 2021 7:39:05 GMT 1
Seems a lot for rings only . So long they are jap made they are good .
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Post by jon on Oct 20, 2021 18:02:51 GMT 1
So, is the consensus that Yamaha/ART made STD, 0.25mm and 0.5mm oversized pistons for LC and YPVS?
If so what’s the story on those rings?
Looking at Fowler’s they mention a 31k piston having a 2GU (banshee) number. Was it always this way, or have Fowler’s just listed the new part number without quoting the old one as superceeded?
Main reason I ask is I have some 31k cylinders rebored to use 2GU pistons made by ART at 0.5mm oversize. I thought they were banshee from the start, but maybe an officially superceeded Yamaha part for 31k in later years?
Jon
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Post by davecroucher57v on Oct 20, 2021 19:27:13 GMT 1
2gu,s dont use expander rings.
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Post by midlifecrisisrd on Oct 20, 2021 20:45:49 GMT 1
Correct, rings are different as 2gu rings don't fit in 31k pistons (well the bottom one anyway)
I've done the same and bought new std banshee pistons/rings to go in good 1ua barrels
Steve
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Post by freddie19 on Oct 20, 2021 20:48:21 GMT 1
On Fowler's website look under 1985 RD350 (57V).
The original rings were all 31K then superceded by 1UA. STD 1UA and 2nd oversize still available to order but 1st oversize discontinued.
2GU are Banshee and as 31K parts are no longer available Yamaha list these as suitable replacements.
If you can't find NOS genuine 31K and want ART quality pistons then 2GU are your only option.
STD Yamaha rings were made by TP Teikoku and highly regarded as superior quality compared to any other manufacturer.
Luckily I've stocked up over the years and have genuine Yamaha 31K pistons and rings in STD, 1st and 2nd oversizes so should be well covered for many years to come!😁
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Post by jon on Oct 20, 2021 20:57:41 GMT 1
On Fowler's website look under 1985 RD350 (57V). The original rings were all 31K then superceded by 1UA. STD 1UA and 2nd oversize still available to order but 1st oversize discontinued. 2GU are Banshee and as 31K parts are no longer available Yamaha list these as suitable replacements. If you can't find NOS genuine 31K and want ART quality pistons then 2GU are your only option. STD Yamaha rings were made by TP Teikoku and highly regarded as superior quality compared to any other manufacturer. Luckily I've stocked up over the years and have genuine Yamaha 31K pistons and rings in STD, 1st and 2nd oversizes so should be well covered for many years to come!😁 Now we are getting somewhere. I realise 2GU piston rings don’t have the expander. I’ve often wondered if an LC bottom ring would fit a a NOS 31k or 2GU ART piston. Anyone on here has the parts and can measure? Jon |
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Post by freddie19 on Oct 20, 2021 21:19:40 GMT 1
I see Fowlers have in stock or available to order 2UA F2/ Banshee pistons and rings in all 3 sizes.
But at £100 each for the pistons and £54 for a pair of rings it ain't cheap....but hey, you get what you pay for!😁
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Post by bare on Oct 21, 2021 18:09:54 GMT 1
Back 'when' these bikes were current.. there were more than 2 oversizes supplied... 4 IIRC
Yama san subsequently stopped doing that though.
Possibly there are a few remaindered oversizes secreted in sheds?
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Post by jon on Oct 22, 2021 17:06:19 GMT 1
Back 'when' these bikes were current.. there were more than 2 oversizes supplied... 4 IIRC Yama san subsequently stopped doing that though. Possibly there are a few remaindered oversizes secreted in sheds? How ‘backwards’ is that? Offer more oversizes when these bikes were newer and less worn cylinders, then as they age and need bigger bores reduce the larger sizes? Must be some reason, but I cannot see why? Jon |
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