Quote:
Originally Posted by GZ300
It's literally a jug and piston swap and it's absolutely practical. The jetting will be nearly the same. The o.p. of this thread way overcomplicated shit and made a lot of guesses and mistakes including the "while I'm in here I might as well" disease. Swap the piston and jug and get on with life.
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I still can't load a pic on this site. It'd be nice.
I just did a big bore with a used Chinese ATV jug and piston I found on ebay for 45 dollars. The jug was over 1mm taller and the sleeve was too large for the case. They make kits on AliExpress which fit the case but I haven't bought one so I can't speak on the deck height of cylinder that comes with the kits.
What I did was knocked the sleeve out, had my machinist turn the bottom which enters the case down to 83.1mm, then had him take half the extra jug height off the bottom of the jug, reinstalled the sleeve, then took the other half off the top of the jug with sleeve installed for a fresh, square cylinder. Piston ended up at essentially zero deck.
I used new rings and gaskets for a 78mm piston. I used the Suzuki piston pin because it fit the ATV piston better than the pin it came with. All in all I spent $155 for a US machined setup that puts out a LOT more power than the stock setup did. It's literally a no brainer as far as cost vs. reward. The power gain is not from the CC's alone but from the increased compression ratio the extra CC's in the cylinder while combustion chamber volume stays the same. The increase is over a point of compression.
My bike now has 840 original miles. Since a 78mm setup can never be bored more, (might get away with a ring and hone at 30-40k) I'll collect, machine and store the parts to replace it in case it ever wears out. It will live the rest of its life as a GZ300.