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Discussion Starter · #1 ·
so i have no clue were to put this thread... but anyways ive searched :google and ive seen that wiseco is better but i want you guys opinion

i just want the longest lasting one... i dont care about performance

this is for a 93 yz80 (if that makes a difference)
 

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I would say Wiseco as well. Junior had a post up about the differences in pistons a while back. IIRC, he got into the differences (good and bad) of the major companies.
 

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yea I did, I can't find it anymore tho. Just keep in mind when going with a wiseco that they generally make 'em in only one size so you're gonna have to fit the cylinder to the piston, which means boring and coating.
 

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That was a good read Junior. :thumbup

IIRC, you covered the differences on how the pistons held up over time, against heat, skirt length, traits/tendencies of each, etc.
 

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Yamaha Forum : Your Yamaha Motor Products Community & Resource - View Single Post - 2009 R1 Hesitation

found it.

All about searching the right terms.

Me said:
actually lately Yamaha have been running powder metallurgy pistons afaik. Good for slap and strength in the vertical, horrible for folding skirts. But you can't win 'em all, it's a matter of picking your poison.

I'm not 100% on what they're using for eggs in that motor tho.

And ya man, to some people FI is new, lol. Altho really any highschool kid should be taught most of this stuff, if they paid attention in auto shop rather than gabbing with their friends about how they were gonna put a big turbo on their civic anyhow. Or a big supercharger on their mustang, pick your poison.

Personally I've always found that Japanese pistons are generally either cast or powder, generally too short in the skirt, and prone to folding, but very light which is a damned good thing because Yamaha conrod bolts are ALWAYS suspect. First part I order for any Yamaha 4-stroke I get my hands on is ARP rod bolts.

North American stuff stock is usually cast, aftermarket is almost always forged. But Wiseco make up something ludicrous like 70% of the market share for aftermarket pistons globally, higher here. So really you're mostly seeing the Wiseco effect.

Euro pistons are my favourite, most of the euro engines I've dealt with are Rotax, very old school, big, tall skirt, cast pistons with thick deck heights (I've seen as high as 0.250" on 'em sometimes, twice what I would consider necessary) Leads to a very reliable piston that doesn't slap, but it's so heavy that it's hell on the rod. we're talkin ~40% extra weight for the same bore of piston, which means a beefier top end bearing and wristpin too, which correspondingly means an even bigger conrod, and it all adds up to a highly stressed botom end that shakes like the San Andreas. BUT with proper design, any amount of stress can be dealt with, usually the trade off is a higher inertia bottom end, but I tend to like to run as much flywheel as I can get my hands on so for me it's ok.

as a quick rule of thumb for piston fits, I generally run 1% expansion for a cast, 1.2-1.5% for a powder and a hair under 2% for a forged. I run 'em a little looser than most guys do tho, you could probably knock 0.2% off most of those figure to get a more "normal" figure.

While I'm gabbing about this shit I should point out that single ring pistons went thru vogue in Rotax 2-strokes from factory awhile back. DON'T DO IT. Not for an engine that's gonna see use off the racetrack. On a motor that's being rebuilt every race, you won't scuff intime. In a motor that's gonna see several hundred or even several thousand hours between rebuilds, it WILL scuff. I've got a couple of Rotax jugs around here with the devils claw marks to prove it.

I've got a GSXR egg somewhere too that got spat sideways in the bore at 17psi of boost, and it was a K4 which is actually one of the longest skirts in "modern" literbikes, there's noooooo rocking support on modern pistons.
If memory serves, Namura buy from factory suppliers, overrun production stuff basicly, at greatly reduced cost. This means that 9 times out of 10 you're buying an OEM part with a different number, which for a newer Yamaha means powder metallurgy, but in your year it'll mean cast likely. Unless the part was superceded, which is possible, bore and stroke have been the same on that bike for 20 years nearly.

hope this helps.
 
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