Piston crossover?

[roostafish]

Is there anyone who has tried to crossover the 250 piston? I've always wondered if I could just grab any old 250 piston from a modern bike and shove it in there. They all have the same bore. Obviously there may be a different deck height or wrist pin, but I'm just wondering. The Gas Gas kits are over $200, which I think is highway robbery.

 

[Rick]

I hear ya, I think my last piston kit for my 200 was right at $200.

 

[Adrian]

I have never seen a spec sheet for 2 stroke pistons. My dealers has lots of different pistons. We looked down that road before. It seems as though we found something that could be used in a pinch, but from what bike eludes me. It was not a desired match. I think it was ported on the intake side and the ring stakes were were close to the ports. A piston with a little more compression distance and a dome with a flatter center would help tighten up the stock squish. I think the Tm 250 is a direct replacement but that doesn't really help availability .

 

[Adrian]

I remember ten years ago the piston alone was $200, and the only one we could get was a Wiesco. When the Vertex ,athena and the wossner became available I gave up the crossover quest. I do wonder if the case reed honda is a closer match.

 

[GMP]

I think the Tm 250 is a direct replacement but that doesn't really help availability .

Yes it is, and you can get them from a Vertex dealer, not a TM only part. Although it is used OEM in a TM, its listed as TM/GasGas and came in a Vertex box. I just installed one recently and have used several in the past. I paid around $120 for my last kit. I still have the box on my workbench at home, I'll post the part# tonight.

I beleive the case reed Honda pistons will work if you have the cyl replated and sized for them, as there is a slight size difference. Jim Cook did this on his old bikes so perhaps he will comment.

 

[Silver]

Where did you get a Vertex for $120 I paid $150.

 

[Jim Cook]

Yes it is, and you can get them from a Vertex dealer, not a TM only part. Although it is used OEM in a TM, its listed as TM/GasGas and came in a Vertex box. I just installed one recently and have used several in the past. I paid around $120 for my last kit. I still have the box on my workbench at home, I'll post the part# tonight.

I believe the case reed Honda pistons will work if you have the cyl replated and sized for them, as there is a slight size difference. Jim Cook did this on his old bikes so perhaps he will comment.

If you hone a GasGas 250 cylinder just a bit, it will take a Wiseco piston kit for a Honda CR250R ('88-'96). (The GasGas bore is 66.40, as is the od of the Honda spec piston. GasGas A-D piston od is 66.33, 66.34, 66.35, & 66.36. All of which use the very same piston ring set.)
This Wiseco Honda spec piston kit uses the same wrist pin bearing, circlips, and same rings as the Wiseco piston for GasGas. (Same connecting rod kit, also.)

In earlier days of limited offerings, every time I had a cylinder replated, I would usually have the finished cylinder custom honed for the Wiseco Honda piston.
That was before I was able to get other GasGas specific piston kits for a reasonable price, and before the Athena (Wossner) non-stick coated pistons. The Vertex TM piston kits became available (through Tucker Rockey) before the Athena kits did.

The Vertex kits generally cost about the same as Wiseco. I really like them, but replacement Vertex ring sets cost about $50; where Wiseco and Wossner ring sets run about $30. After Athena piston kits became available, I liked them so much that I rarely used anything else for a stock cylinder.
(They are the same Wossner piston as the OEM GasGas piston; except with a coating on the piston, like the Vertex.)
Does anyone know who is selling the Athena pistons now, and how much they are going for? (I've still got a good selection of rings, but it's time for a new piston for for my 300.)

Good Riding and Wrenching!

Jim

 

[HydroDog]

They might be all the same bore but are they all the same height from wrist pin to top of dome?

I was just reading a artical a couple months ago on a KTM 300(I can not remember which rag, Dirt Rider I think) but they installed the GG piston instead of the stocker because it was lighter and more compression.

 

[Jim Cook]

They might be all the same bore but are they all the same height from wrist pin to top of dome?

I was just reading a artical a couple months ago on a KTM 300(I can not remember which rag, Dirt Rider I think) but they installed the GG piston instead of the stocker because it was lighter and more compression.

Yes. There is a bit of difference in the skirt of the Honda and GasGas pistons, but otherwise they are the same.

To my knowledge, the KTM and GasGas pistons are not such a close match.

When GasGas started building their own 250 engines for the '96 year model, they kept the same piston that was used in the previously used TM 350cc engines.

Jim

 

[stainlesscycle]

They might be all the same bore but are they all the same height from wrist pin to top of dome?

I was just reading a artical a couple months ago on a KTM 300(I can not remember which rag, Dirt Rider I think) but they installed the GG piston instead of the stocker because it was lighter and more compression.

it was a husky 300 they installed a gasgas piston in...

 

[Jim Cook]

it was a husky 300 they installed a gasgas piston in...

Thanks for that information.

I'm still researching the Athena piston availability and costs.

Jim