[GS 650 bottom end on gs 550 base] need I absolutely machining the base to fit jugs?

[Guest]

Hi all

The whole question is in my subject...

I want to put gs 650 bottom end (jugs....) with the head and pistons on my 550 6 speeds base. I'm preparing all the parts, but I planned to not disassemble all the motor.... Is it plug and play between the 650 bottom end and the 550 base or do I have to disassemble the base to enlarge anything to be able to put the 650 bottom end?

thanks!

[DimitriT]

It appears the only difference between the two blocks is the 6mm of larger bore on the 650. (62mm vs 58mm)

So it sounds like its doable so long as the stud pattern and location of the oil channels line up. Are the valve sizes the same? Will you get enough flow through the 550 head?

I recall people discussing the option of putting a 550 head on 650 cylinders as a way of increasing compression but maybe someone else can add info.

[steveb922]

650 barrels won't fit directly onto 550 crankcases. You'll need to grind away a relatively small amount of metal. Theoretically, you could do this without splitting the crankcases, but you would run the risk of putting swarf and grindings into areas where you could not remove them ie the crankshaft.

[mikerophone]

I see to recall reading that people put a 650 head on a 550 bottom end?

[boris.h]

Thanks. Do not find any picture of the cranckase before and after grinding to locate areas..?

[tkent02]

It took a LOT of grinding on my 550, millions of particles flying every which way. NO chance I'd attempt it without splitting the cases. The good news, splitting the cases is easy.