Rebuild

[hadfield4wd]

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?

[TheLetterJ]

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.

[savage sausage]

Originally Posted by hadfield4wd

Looking at wiseco piston and athena gaskets. Any reason not to?

1999 ec 250

Thanks.

thats whatI am buying now athena,also I already have a honda cr250 forged wiseco to go in.

I paid about 50 pounds brand new in the box off ebay.....miles cheaper than a specific GG one.

[barossi73]

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

[hadfield4wd]

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.

[Jakobi]

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).

[TheLetterJ]

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:

[hadfield4wd]

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.

[hadfield4wd]

Originally Posted by GGRider01

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

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

[GGRider01]

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/B00...=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.