Pistons GP 246 GP 292 GP 643

[vmaxdad8657]

A Yamaha GP 246 and GP 292 have the same bore?
The stroke is shorter on the 246, is this correct?

And a Yamaha GP 643 piston can be used on a GP 292
if you bore the cylinder.....making it approximately 321 cc.

Will the GP 643 piston work in a GP 246 if it is bored to fit?

 

[900zrcat]

I know that the piston skirts are a different length between a 246 and 292, so they won't interchange. i never heard of putting 643 pistons in a 292 though.

 

[montynormand]

643 pistons are run in the GP292's more that people know. Yes the 246 (et250) has a shorter stroke - I would check the piston pin position before you get carried away

 

[900zrcat]

The piuston pin height is the same, the skirts are about a half in shorter on the 250 piston. Not too good for a piston port engine.

 

[montynormand]

normally you shorten the intake skirt anyway in order to gain more intake timing

 

[900zrcat]

FYI a 643 piston has a different pin hieght so it won't work in either motor. Anyone wanna buy a 643 piston.

 

[montynormand]

FYI a 643 piston has a different pin hieght so it won't work in either motor. Anyone wanna buy a 643 piston.

Really??? hmmmm how did I run them in my GP292 race sleds then?

 

[900zrcat]

Am i missing something?

 

[900zrcat]

 

[900zrcat]

 

[YamahaRacer]

Trying the pic[/QUOTE]

Looks good to me, bump that cylinder up.

 

[patsxr700]

lol looks like u would have to bump that cylinder up alot ....

 

[YamahaRacer]

lol looks like u would have to bump that cylinder up alot ....

Like Monty said, a lot of people have done it and i can back that up.

 

[montynormand]

Very easy ..... extra gaskets or make a spacer.
The phazer piston is a good GP300/SR292 conversion too, but you also need to add base gaskets

 

[900zrcat]

Ok I have the parts so I'm going to give it a try. Port timing is going to be a little tricky though. Thanks for the info.