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Post by Mr M T Pockets on Sept 1, 2016 21:31:10 GMT 1
hi i might need a re-bore on my bike and would like to know a recommended pistons kit, i have been looking at these on ebay at the moment ,,YAMAHA RD350LC YPVS 350 BANSHEE YZF NAMURA Hi Compression PISTONS 6BHP OVER ST, are they worth a shot, any suggestions thanks steven
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Post by markhoopy on Sept 1, 2016 21:45:21 GMT 1
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Post by bare on Sept 1, 2016 23:05:41 GMT 1
Depends on the size of your Bore Holes :-)
IF within the 2 oversizes that Yama still (?) supplies oem pistons for ??
Then that is THE clear and superior choice.. period !
Pistons/rings/wrist pins and needle bearings.
No One supplies equal, let alone superior quality pistons/bits, All brochure babbles aside.
Vertex are good (possibly best?) Wossner are claimed good but quality control hasn't been outstanding,
Pro-X are decent.. but basically a box containing whatever jobber product was available.
Riken rings work OK but don't hold a candle to OEM ones
Wiseco are well made products Nice thin rings and tapered bore wrist pins.. There remains that 'Forged' bugaboo though. Love 'em Or Hate 'em.
The Namura etc are IMO sketchy buys. But some claim happy usages.
Buy Cheap.. buy Twice and if dim; repeatedly.
Bit of a Jungle out there G'luck
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Post by dusty350 on Sept 2, 2016 7:27:11 GMT 1
Hi I ve always used Mitakas, supplied by PJME when they rebored my barrels. I'm sure plenty of guys here have used them with good results. Dusty  |
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Post by jon on Sept 2, 2016 7:54:22 GMT 1
I too have used Mitakas (Japanese ones) for a few builds now. I think PJME are the official importers of them?
Those Namura pistons sound like a good idea. I suspect the wrist pin to piston crown is slightly more than normal to take into account the majority of huge squish gaps these bikes seem to have.
It's got me thinking though. I always thought Yamaha did this because they were unsure of a build up of tolerances making the squish too small? However I haven't seen or heard of an acceptable squish without fettling. If this were the case these Namura pistons would be a time bomb in certain engines. Therefore I can only conclude that ALL RD engines were given more than normal squish. If so, why were Yamaha doing this?
Jon
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Post by midlifecrisisrd on Sept 2, 2016 9:36:43 GMT 1
As Jon says I'd worry about squish.
They can only have a higher crown to pin measurement or the dome on top of the piston is more pronounced.
Both will affect squish but altered dome shape will affect head volume.
If you want higher compression get a reborn as intended using mitakas then check squish before getting the head skimmed to suit
Steve
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Post by bare on Sept 2, 2016 18:54:34 GMT 1
I too have used Mitakas (Japanese ones) for a few builds now. I think PJME are the official importers of them? Those Namura pistons sound like a good idea. I suspect the wrist pin to piston crown is slightly more than normal to take into account the majority of huge squish gaps these bikes seem to have. It's got me thinking though. I always thought Yamaha did this because they were unsure of a build up of tolerances making the squish too small? However I haven't seen or heard of an acceptable squish without fettling. If this were the case these Namura pistons would be a time bomb in certain engines. Therefore I can only conclude that ALL RD engines were given more than normal squish. If so, why were Yamaha doing this? Jon Yamna also sent out their Proddy racer TZ's with 'Lowered Compression' as well :-) They simply didn't trust their customers with their engines. Consequently they went to 'big' squish on production bikes..as simple insurance against inept users/damaged engines/warranty claims. Also why Press release Lc350's made ~10 more hp than the ones on the sales floor. Sneaky Rascals. Still at it.. a while back with R6 engines with a claimed 16K redline and altered tachs to hide their Real 13k one. |
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Post by jon on Sept 2, 2016 19:30:05 GMT 1
Bare, what you say makes sense and is logical, however I wonder what the guy at Yamaha who made the decision at the time 'really' was thinking. After all surely they were competing with other Japanese manufacturers to offer the most powerful bike, for the consumers?
I do wonder whether they were relying on press with 'fettled' engines on track or magazine to convince the punters?
Jon
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Post by steven on Sept 2, 2016 19:44:44 GMT 1
Hi,
My understanding of the reasoning behind mass produced 2 strokes leaving the factory with rather large squish bands is to do with the problems encountered with tollerances on mass produced parts.
ie, if the tollerances on con rods and pistons is at the upper end of the tollerance, and the cylinder is at the lower end of its tollerance, then there is a danger of the piston hitting the cylinder head.
So, manufacturers delieberately make the squish band wide to make allowances for the worst possible parts size combination.
steven.
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Post by Mr M T Pockets on Sept 3, 2016 0:05:56 GMT 1
thanks every one ,i will get some makitas
sorry Mitakas
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