Rebuild

What do you mean?

Those are both fine products, if that's what you're asking. Check your cylinder for a letter, either A, B or C. Get the corresponding piston.
 
Oh What is the difference between a, b and c? I've used many wiseco's just never worked on a gg didn't know if there was any special snake oil. Like you said the letter thanks.

Wiseco only lists one piston
 
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S3 makes the GasGas OEM piston, if I recall - they have A, B and C pistons. Most any Japanese and European two stroke uses that same lettering system. It denotes, I think, an increase of .01mm. A heavily used A cylinder may measure out to be a B cylinder, but without precision measuring, why take the risk of accelerating the wear of an already used cylinder? Granted, there is a bit of leeway here, and many people go up a size with each rebuild. I think it may be even more critical when unsure of cylinder size to get your ring gap set correctly.

The original cylinder on my GasGas was unmarked. It also had spots of aluminum showing through, so being impatient I just replaced it. I was sent an A cylinder and ran an A piston.

Here are the Wiseco part numbers for the EC 250. The last letter indicates size. I added the size next to the part number to show the difference.

01.7307.A - 66.33mm
01.7307.B - 66.34mm
01.7307.C - 66.35mm

If you haven't already found a source for the gasket kit, this one is what you need and the price is fair. It doesn't take them long to get it in and ship it to you either. https://www.amazon.com/gp/product/B00IRWLXRM/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1
 
hadfield4wd said:
Oh What is the difference between a, b and c? I've used many wiseco's just never worked on a gg didn't know if there was any special snake oil. Like you said the letter thanks.

Wiseco only lists one piston
Click to expand...

While I have an EC200 I am following your progress. Pictures and some videos would be great! I'm learning and need to replace my top end soon.

Keep us posted.
 
12Bravo said:
While I have an EC200 I am following your progress. Pictures and some videos would be great! I'm learning and need to replace my top end soon.

Keep us posted.
Click to expand...

Well I'm not sure that I'll get video. I'll take pictures. This is not my first rodeo. I've rebuilt dozens of bikes/atvs. This is just my first GG. So I want to learn as much specific stuff I can.

GGRider01 said:
S3 makes the GasGas OEM piston, if I recall - they have A, B and C pistons. Most any Japanese and European two stroke uses that same lettering system. It denotes, I think, an increase of .01mm. A heavily used A cylinder may measure out to be a B cylinder, but without precision measuring, why take the risk of accelerating the wear of an already used cylinder? Granted, there is a bit of leeway here, and many people go up a size with each rebuild. I think it may be even more critical when unsure of cylinder size to get your ring gap set correctly.

The original cylinder on my GasGas was unmarked. It also had spots of aluminum showing through, so being impatient I just replaced it. I was sent an A cylinder and ran an A piston.

Here are the Wiseco part numbers for the EC 250. The last letter indicates size. I added the size next to the part number to show the difference.

01.7307.A - 66.33mm
01.7307.B - 66.34mm
01.7307.C - 66.35mm

If you haven't already found a source for the gasket kit, this one is what you need and the price is fair. It doesn't take them long to get it in and ship it to you either. https://www.amazon.com/gp/product/B00IRWLXRM/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1
Click to expand...



So I was hoping to order the piston today. However I'm out of town till Friday. So you're basically saying to pull the piston to check the letter and get the same? I don't think it's that worn, there is no discernable issues, however it's the original piston on a low hour bike, this is preventative and piece of mind for my.

Also is the cylinder nikasil'd.

I really appreciate the knowledge on this site.
 
No need to pull the piston. The letter will be stamped on the outside of the cylinder, unless like mine it isn't. I don't know if they used nikasil or something else, but it is plated.
 
The cylinders are plated. The letter (if present) will be at the rear of the cylinder, all the way near the bottom where it meets the cases, should be visible with cylinder still installed.

I actually intentionally ordered a "C" piston for my ~200hr "A" cylinder and it fit PERFECT... but in the end, I just wasn't comfortable with the condition of the plating so now I'm sending it off to have it re-plated anyway... should have just bought an "A", oh well.

On a similar note, A, B, and C pistons all use the same rings. I did not have to file my rings to get the proper end gap, but with a new A cylinder you probably would need to.
 
hadfield4wd said:
Well I'm not sure that I'll get video. I'll take pictures. This is not my first rodeo. I've rebuilt dozens of bikes/atvs. This is just my first GG. So I want to learn as much specific stuff I can.





So I was hoping to order the piston today. However I'm out of town till Friday. So you're basically saying to pull the piston to check the letter and get the same? I don't think it's that worn, there is no discernable issues, however it's the original piston on a low hour bike, this is preventative and piece of mind for my.

Also is the cylinder nikasil'd.

I really appreciate the knowledge on this site.
Click to expand...
If the engine sounds good and is a low hour unit I don't feel it's worth it to pull it down for piece of mind. Run it. Mine was a low hr 2000' when I got it and still has the oe top end w/no issues. BTW I am a preventive maintenance kind of guy when needed. What is the comp. psi?
 
Well a piston is cheap. So I'm OK with it. Reeds as well are going in. Gasket kit is ordered thanks.

So if i have an "A" get a "B" right? Is that what I am hearing?
 
It's only a .0003" (yes, three/ ten-thousandths) difference, so even if your cylinder is still in spec for A, using a B won't hurt anything in my experience. I've never put an A back into anything.
 
wossner also make piston,for some reason the 'b' was more $ than a or c.
you will need to remove the exhaust spigot to get wiggle room.
leave the coolant 't' on the head,and remove hoses instead,or be prepared to replace gasket(not in topend kit)
be careful of coolant drain washer,mine disintegrated as i removed it.
smallend needle bearing is cr250/yz250,check width against the one you remove,as the bearing supplied with my wossner was narrower(replaced with correct)
when installing jug you have to start with it leaning a little back towards carb and roll it forward into position as you get piston started in bore
 
So just talked to my son about the GG. I had him go look at the piston. he's 17 and has rebuilt top ends before. So he knows his way around a bike. He did not see any letter on the back of the piston. So do I roll the dice and order a B? This way I'll have it this week so I can get it together quickly or do I pull the cylinder and measure and get the perfect one. It seems if the rings are the same it won't make that much of a difference.
 
Not sure re the older models if the cylinders are stamped at the back down low just above the case intake. I've used S3/Vertex OEM and Wossner pistons and the size is always stamped on the dome of the piston along with the arrow indicating the front of the engine.

Here are a couple of threads I put together a few years back.
Converting OEM 300 to a 250cc with replacement head and jug - http://www.gasgasrider.org/forum/showthread.php?t=11970

Bottom end rebuild (same bike at 260hrs) - http://www.gasgasrider.org/forum/showthread.php?t=14730

There is significant depth in there regarding squish clearance and head modification as well as port timing. Highlights a few of the issues I personally encountered during my learning curves (having not a lot of experience prior).
 
This is what I was talking about, "A" stamped on the back of the cylinder:



You can also see that the last digit of the part number (this is for a 300, not a 250) on top of my new Wossner piston is "C"

I think going with a "B" as you proposed is a safe bet, it will fit a used "A" cylinder better, and I don't think there were "C"s from the factory... it was either an "A" or "B" as far as I know.

Edit: here's some funny stuff! I just looked at my old (factory) piston and it is a "B"... stuffed in an "A" cylinder from the factory! I scrubbed the top with some brake clean and a wire brush so you could make out the numbers:

 
Well I may be an idiot. I had my son looking at the piston skirt through the reed hole. haha I'll send him that picture so I can order my piston.
 
GGRider01 said:
Here are the Wiseco part numbers for the EC 250. The last letter indicates size. I added the size next to the part number to show the difference.

01.7307.A - 66.33mm
01.7307.B - 66.34mm
01.7307.C - 66.35mm
Click to expand...


so after a bunch of research the part numbers above are ProX numbers not wiseco. I ended up buying a wiseco forged piston. They only come on one size they don't have a A, B or C
 
Interesting, I didn't know that. I got those from Wiseco's website, if I recall. By the way, before tearing into it, I highly recommend getting one of these for the rebuild. http://www.amazon.com/gp/product/B0...rue&ref_=ox_sc_sfl_title_1&smid=ATVPDKIKX0DER

It's that or use a standard 13mm wrench and put a half inch drive torque wrench in the open end at a right angle to the wrench to torque the cylinder down. There are two nuts that reside behind the power valve covers, one on each side. This tool will make it much easier. Using it at a right angle negates the need to do math to get the proper torque specs with the adapter.
 
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