FJ/FZ/YX 600cc Big Bore Piston

Stumbled upon an older thread on here where someone mentioned that the pistons from the Kawasaki KZ650 are nearly identical to that of the pistons in the FJ/FZ/YX 600 engine. I'm in the middle of building a radian engine to stuff into my Seca 550 and was curious to see if I could make these pistons work as any previously made big bore kit for this engine is now obsolete. Wiseco used to make 61mm pistons for this engine (652cc), however the pistons from the KZ are 62mm. Anyone have any comment on cylinder sleeve thickness for this overbore? If 61mm worked, is there any danger thinning out the cylinders another 0.5mm?

I found a set of KZ650 Pistons on ebay for $35 so thought I'd take the risk.

From initial inspection they are extremely similar, the stock piston has extra oil holes on the side whereas the kz piston does not, additionally the valve recess on the stock piston is deeper than the Kz.

Here are some pictures comparing the stock yx600 piston to the kz650 piston. Measurement are also included.

With 62mm pistons the final displacement of the engine would be 673cc.

Let me know what you guys think in regards to feasibility.

 

This makes me nervous................

Really, really nervous.

 

Yeah certainly things that can't be overlooked, obviously valve to piston contact needs to be checked. Machining the valve recess is not unheard of but there are a lot of factors to consider.

 

Like whether there is enuf material there.........


Also, some Yamaha engines lubricate the cylinder walls via "splash" thru the pistons (thus the oil holes), where other use a pressurized spray of oil thru a hole in the rod bearing and the rod. I don't know which style the 600 engine uses, better check and make sure.

 

Thanks for the info! I've got my work cut out for me.

 

I think I once worked out that Kawa 305 twin pistons would be close match too. But then you need two bikes worth..

J