wiseco piston question

maxwell

maxwell

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So I have an older sled with about 4k miles on it. Nikasil Cylinders. My question is:

I would like to either replace the rings or replace the piston entirely for "safety" purposes.

If the stock piston is say 76.5mm and a wiseco piston is 76.5mm, should I just have the pistone honed out and slap the new piston in (if it mics out correctly with the correct tolerances) or should I have new nikasil applied?

I think I may have answered this question myself after I had typed this.
 
you shouldn't need to oversize a nikasil bore any, wiseco pistons are generally only good for about 3K miles before the skirts start to collapse your stockers might be fine yet. rings is no big deal, just hone the "glaze" off the nikasil and you're good to go.

nicasil won't really wear down, atleast not noticably I've never seen one out of spec, they just get munched up in burn-downs.

as far as your stock pistons, the only real concern is skirts collapsing, the best way I've found to check this is to run a micrometer around the bottom of the skirt and the top of the piston and make sure it's the same measurement, and it's not out of round at the bottom.

if it is, then the piston will rock back and forth in the bore and cause you to lose compression under load, plus it'll screw with your time/area curves on the porting, since the port will be opening abit early or abit late, squish would also be effected. those effects are all negligable when compared to the power loss from loos of compression tho.


hope that helps some!
 
Junior...i Got A Question...why Are A Lot Of People Against Wiseco Pistons?is It Because Of What You Just Described? I Recently Put A Set In My Viper And So Far I Am Happy. There Are People On This Sight That Won't Use Them... I Did Mainly For Price...245.00 For A Matched Set,includes Wrist Pins And Circlips And Of Course Rings.i Do Realize That You Get What You Pay For But Oem Pistons From Yamaha Are Very High Priced!!!
 
Thanks,

That made sense. I will just measure them. So you wouldn't even recommend changing the rings to a new set? Maybe I should just do a compression check first, then ask quetions later.

Yeah, What aftermarket pistons would you recommend?

Junior said:
you shouldn't need to oversize a nikasil bore any, wiseco pistons are generally only good for about 3K miles before the skirts start to collapse your stockers might be fine yet. rings is no big deal, just hone the "glaze" off the nikasil and you're good to go.

nicasil won't really wear down, atleast not noticably I've never seen one out of spec, they just get munched up in burn-downs.

as far as your stock pistons, the only real concern is skirts collapsing, the best way I've found to check this is to run a micrometer around the bottom of the skirt and the top of the piston and make sure it's the same measurement, and it's not out of round at the bottom.

if it is, then the piston will rock back and forth in the bore and cause you to lose compression under load, plus it'll screw with your time/area curves on the porting, since the port will be opening abit early or abit late, squish would also be effected. those effects are all negligable when compared to the power loss from loos of compression tho.


hope that helps some!
Click to expand...
 
Wiseco pistons are forged as opposed to cast(stock), with forged pistons you need to run larger clearences to compensate for the extra expansion. It is common to hear piston knock when cold and longer warm-up is often reccommended.
The stock cast pistons are made by Nik's/ProX for Yamaha; In Ontario Canada, the Nik's/Prox pistons are 40% less than dealer price. We personally have had bad luck with Wiseco pistons that we used in watercraft and ATV's.
 
srx and viper pistons are not cast, they are powder forged. The other yamaha pistons are cast, but on the viper and srx.
 
yam-srx-viper and wiseco's

yamahaulic is right. The stock viper srx pistons are a powder forged unit, they provide great strength and minmal bore expansion, which relates to better ring seal because they can be run with a tighter skirt to side wall clearance.

Wiseco pistons come already to go into your stock cylinder, they are the correct size, expansion rate already factored in. You dont hone out your plated cylinders for them. The wiseco piston is lighter then the stock yamaha unit is, and they use a thinner ring then stock, which is less drag on the cylinder wall, the wrist pins are lighter as well,but its not anything your gonna notice in a trail sled. For trail riding the yamaha has the bigger advantage, in being the rings are thicker and wil last a longer duration then the wiseco will.
 
another thing with wiseco's is the higher silicon content, just like a hyperutectic piston they can be brittle. oem are best.
 
A well known yamaha dealership told me I should stick to stock pistons for my srx 600, he said the stock pistons are better then wiseco's. Now these people been in business for over 30years and are well known, so if they say no, its a no-go for me.
 
good info all around, I like the wisecos for the weight difference, but yes, they are forged as opposed to the forged powder metal (which is a REALLY cool process by the way) on a stock bore SRX tho I'd likely go with an 01-02 SRX piston.

I find that the forged pistons tend to collapse skirts faster than cast (because of the malleubility difference I imagine. but I haven't seen a powder forged piston collapse a skirt. that said, I was pretty far removed from the dealership by the time those sleds had enough miles on 'em to be needing new pistons.

it's all a tradeoffs, just gotta go with whichever one fits you and what you want to do with that motor the best. I also find that the thinner rings are less likely the get eaten by a port, might just be coincidence tho, but that's another argument for the wisecos, they seem to be less likely to wreck a cylinder when they go
 
I heard that stock 2002 vipers had a different piston than 2003 vipers. Yamaha had issues with the 2002 piston and QUIETLY replaced the 2002 piston part # with the 2003 piston part#. Anyone know anything about this?
 
SledBoy said:
I heard that stock 2002 vipers had a different piston than 2003 vipers. Yamaha had issues with the 2002 piston and QUIETLY replaced the 2002 piston part # with the 2003 piston part#. Anyone know anything about this?
Click to expand...

not to my knowledge, but it's possible, I BELIEVE that the vipers use a different piston from wither the 98-99 cast SRX piston and the 00+ powder forged SRX piston. I think it was supposed to be a cheaper/lighter piston for the vipers. could be that they superceded it to the powder forged SRX one quietly
 
i dont know if they are the same, but shadetree sells oem pistons for 45 bucks a peice complete with pins, rings and circlips, which is cheaper than the wiseco ones they sell, they also sell a high-pro piston from wiseco which is a little more than the other wiseco pistons but not sure what the difference is. and why are the gaskets so much for the viper..
 
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