Piston issues :/

[Lloyd]

Hello guys. I have some piston issues with my rebuild of a ec125 -05. The piston that was in it was a flat top and the one i ordered from w?ssner got a domed top. From what i understand, wiseco is the only manufacturer that makes flat top pistons to my bike so the question is if i have to order a flat top wiseco or if i can fit my domed top w?ssner in any way? Thanks in advance and im from Sweden so excuse me for my bad grammar

 

[noobi]

Hello guys. I have some piston issues with my rebuild of a ec125 -05. The piston that was in it was a flat top and the one i ordered from w?ssner got a domed top. From what i understand, wiseco is the only manufacturer that makes flat top pistons to my bike so the question is if i have to order a flat top wiseco or if i can fit my domed top w?ssner in any way? Thanks in advance and im from Sweden so excuse me for my bad grammar

I had exactly the same problem as you are having. I believe the outcome was that the flat top piston is matched to the head, so using a domed piston with a head designed for flat pistons is a bad idea as the squish angle and height gets all screwed up. However I believe you could have the head re machined to match up to the domed piston.

I also think that both the CR125 and YZ125 use essentially the same piston as the GG125, so maybe you could find another brands flat top piston for either of those bikes. I know for certain that the wiseco piston I run in my GG has CR written on the box and it runs fine.

 

[Lloyd]

Thanks for the quick answer. My fears came alive then.. So there is no way to get the domed piston to fit without machining the head? Not even with multiple gaskets?
/Lloyd

 

[Elvis74]

YZ and CR pistons are quite the same, but the old 125 with TM Motor have the dome and the models after '00 or '01 have the flat top piston

by the way, I have a new 56mm big bore Wiseco flat top piston here which I don't use.....

where are you from?

 

[GMP]

Not quite. The early GG125s with their own motor('01 to '04 I beleive) had a domed piston. I put '00 YZ125 pistons in the one we had. I think there was a change to a flat top configuration around '05.

 

[Lloyd]

I talked to the dealer a few hours ago and told him the problem and he insisted that it was the right piston and told me to install it, if it didn't work i would get my money back. According to him it was the only piston w?ssner made to the 125 and on the package it say it is to 01-09.. I dont wanna ruin my new cylinder/cylinder head due to bad knowledge from the dealer but on the otherside i really want to ride this weekend.. The squish in the cylinderhead is flat so i figure it must be a flat headed piston, otherwise the squish would be at an angle to be used with a domed piston, right? Shall i install the piston and hope for the best or shall i order ? flat wiseco and wait a week? Please help me

 

[(F5)]

ok so its an old bike that would have had a piston before, no guarantees that the last one was correct.

Simple question. Is the head squish shape flat or angled? That's your answer to what piston you need. You seem to be saying that you have a flat head & are holding a domed piston. Sorry but that is a bad combination, worse than the other way around but both are bad.

Do not run it like that, it is likely to at best perform badly, at worst hit the head, blow o-rings &/or detonate. Negative squish angle should be avoided.

Seek you the right piston or find a competent tuner to machine the head to suit the piston (which may, or may not be possible due to spark plug height). But you need someone who knows what they are doing & can correct compression ratio, squish etc.

I'd find the right piston & go wave the head at your dealer (who will probably identify it being from a different year to what he was told it was, or just turn a bit red).

 

[Elvis74]

I am riding a 125 as well, so please post a picture of the cylinder head and I will tell you.
The squish should be between 0,9 and 1,2 mm for the 125, means you can run a 0,15 or 0,3mm gasket

Woessner part no.

8079DA => domed top
8080DA => flat top

 

[Lloyd]

Thanks Elvis! My dealer insisted that the domed one would fit and said that w?ssner made no flat headed piston and that part no really made My day! Problem solved, cant thank you guys enough!

 

[Elvis74]

http://www.wossnerpistons.com/produ...sner-piston-gasgas-mc-54-mm-bore?cookietest=1

 

[Jakobi]

Thanks Elvis! My dealer insisted that the domed one would fit and said that w?ssner made no flat headed piston and that part no really made My day! Problem solved, cant thank you guys enough!

Moral of the story is don't believe everything the dealer tells you. I've found most bike shops in general either tell you what they think you want to hear to make a sale, tell you what you don't want to hear to make more sales, or tell you whatever they want/think because they're too lazy to look into things properly.

This forum really is the number one resource for these bikes. Between everyone here there is always someone truly knowledgable regarding specific information. Unlike other forums you don't seem to see too many people making claims to know things they don't. This place is the BEST!

 

[(F5)]

wow that blows it open, nice post. Nothing like wiping the dealers nose in it than "here's the part number for the non existent part"

Its a sad state of affairs when these days I seem to find most parts guys know less than I do about their product & I'm no expert, you'd think they would do more to keep up to date. Been spoiled by flatting with a guy that knew part numbers off top of his head for heaps of stuff (in a particular field) or could get his hands on the info in a flash. That was many years ago now though.