What Brand of Piston

[noobi]

Im sure this has been discussed before, but the search just finds every thread with piston in it...

So what I would like to know is what brand piston is better.

So far im considering either a ProX, Wiseco, Wossner, or Athena

I know the pros and cons of a forged v cast piston.

A bit of history about the bike, its an 07 EC125, the cylinder has an A stamped on the back, and when i changed the piston the first time the piston that came out had a D stamped on it.
Right now it has a wiseco CR125GP piston, which is what the wiseco site recommends for my bike, but its got around 70 hours and it seems to be getting a bit tired, so the question really is should I replace the piston with another CR125GP, or try another brand of piston???
there is a distributer who sells Wossner forged pistons at nearly half the price of wiseco pistons, but im skeptical as to whether he would have gasgas specific pistons

 

[Debi]

I went with the Wossner for my 03 EC250 and works like a charm. I did order the kit through North Tahoe Motorsports...I called vs ordering it through ebay...this way I made sure he had it...
Great customer service at Tahoe


Good luck

 

[GMP]

I use the Vertex, but 70 hrs on a 125 is nothing to complain about!

 

[widebear]

Pro x is Japanese, cast oe grade and least expensive of the big four. Vertex is allso cast, a light piston that has a moly coating for break in. Athena is a Wossner with a moly coating for for the resellers market, 28 grams heavier than a Wiseco,250 ec piston but very,very good alloys. Wiseco is forged , lighter than the last two and very good rings. If I were in your shoes, economicly speaking, I'd look into a piston from India sold in America under the name Namura http://www.namura.com/contact.htmra . Like pro x but cheaper you'll prob get two for the price of one of the forged ones, You,ll have a fresh top end for a whole season, caveat. you'll need to cross referance a application.

 

[noobi]

Im considering the wossner forged piston. these pistons come in A,B,C sizes. A being 53.95mm, and each size after a 0.01mm oversize.
considering the bike had a D piston in it, should i assume it can take a C size wossner?

the wiseco GP piston is 53.94mm, which is alot smaller than a D size piston...

 

[stay_upright]

I wouldn't assume anything - the two manufacturers A B C sizes are likely to be different.

FYI I measured the bore on my 05 300 and it came out a nominal size or 0.01 smaller IIRC.

Therefore to meet the GG recommended clearances I needed an A piston or the smallest one available and my bike has a lot of use on it! as a note a larger piston was fitted previously and had scoring, maybe due to being oversize. Have a look for any scoring on the piston that came out may be a big clue, if not I would probably go for a 'standard' (b?) piston rather than a large one unless you have any measurements/proof your bore is well worn or more likely was manufactured oversize from nominal (maybe why a large piston was in there to start with?)

Alternatively you could find some-one to measure it..

If the bike is warmed up gently prior to riding it hard I'm sure this is less of an issue.

 

[dave948]

With the coated cylinders the jugs out last a lot of piston and ring sets. Make sure you have an accurate measurement of the cylinder before you order your piston. Keep in mind you need the right tools and knowledge to do this right. Most people who don't do this for a living can't give you a repeatable measurement in the range you need.
Pay a pro $25 bucks to give you the right information.

 

[noobi]

ill get the cylinder measure when i pull it apart.
I ordered the B size wossner, 53.96mm
theres so much riding available around where i am that there isnt really an off season. sand forests in winter, everywhere else in summer.
so i cant really afford to have the bike apart while i wait for a piston from Germany...

this is what the piston looked like when it came out

this is not the piston that is in the bike now.
the bore had no scoring on it at all with this piston

i dont know what the gasgas recommended clearance is supposed to be

btw i ALWAYS warm the bike up before riding, untill theres plenty of heat in the radiators

 

[widebear]

I've seen worse out of my own bikes.

 

[jiauka]

This piston looks fine yo me, i would put new rings and run another season with it.

 

[GMP]

With the coated cylinders the jugs out last a lot of piston and ring sets. Make sure you have an accurate measurement of the cylinder before you order your piston. Keep in mind you need the right tools and knowledge to do this right. Most people who don't do this for a living can't give you a repeatable measurement in the range you need.
Pay a pro $25 bucks to give you the right information.

+1 on this! Unless you have a calibrated bore mic and know how to use it, have it measured properly. The margin of error with lesser methods will exceed the difference in dimmensions you are trying to determine.

There is a fatigue factor to also consider with regard to piston service, so replacing it at 70 hrs is not a bad idea for a 125.

 

[noobi]

+1 on this! Unless you have a calibrated bore mic and know how to use it, have it measured properly. The margin of error with lesser methods will exceed the difference in dimmensions you are trying to determine.

There is a fatigue factor to also consider with regard to piston service, so replacing it at 70 hrs is not a bad idea for a 125.

its up to 85 hours now...

i will measure the bore before i put in the new piston.

BUT

the wossner has a domed top and the other pistons iv run have had flat tops.
although the wossner catalogue lists this piston for 03'-09'

will it be ok, or will the compression be too high and grenade the engine???

 

[GMP]

That changes the game, you can't just do that. I'm sure the head is cut different as well for the flat top piston. The older 125s like the '01 I work on run the domed piston ('98 - '00) YZ125. They went to the flat top some time after that.

 

[dave948]

The take out looks good but at 85 hours it don't owe you anything.
I've never owned or worked on a GG 125 so I can't tell you if it had a flat top or domed piston stock but some one will speak up with the answer I'm sure. Check your clearances before you go too far or you'll loose a lot more than 2 or 3 days riding.

 

[widebear]

Noob. Its time to get out the play dough. Install the old piston without circlips. Roll about a forefingers lenth about a pencil thick or less and place it on the head surface of the piston, install head without orings and rotate the crank about a quarter turn, remove head and measure the thickness of the play dough, replace with new piston and measure again, refer to measuring squish article in tech forum. You might get lucky. If its close to original in the squish boundry do a compression test and see what you get. anything over 200 psi is going to be dicey. Flat tops were used to provide a little more hit in the midrange on moto x bikes.

 

[noobi]

im just gonna return the wossner for a refund, then get another wiseco. which is slightly more expensive.

I wouldnt mind doing the play dough experiment but if i scratch the wossner while testing then i cant return it, if it wont work.

thanks anyway