Overhauling my G-9.. cylinder bore ??

[joefixit]

Hey all, Well I have a dilema,, The cylinder bore on my engine is excessive and too much clearence between .50 mm oversized piston . Can I bore out the sleeve a little more and install a 75.0 mm piston and rings??
The research I have done shows the G-14 stock piston is the same except just bigger diameter..I know there seem to be a few concerns in my own mind such as changing the whole volumetric effeciency of the design, cylinder heat,compression etc etc. Any thoughts and suggestions would be greatly appreciated. Thanks Joe

[kogieblack]

Upgrading to 75 is the best alternative now. US$50 for a new set of piston and rings.

[Flintrock]

Joe, sounds like you have done your homework. It's uncharted ground so as long as it's your own cart, what do you have to lose?

[lady bug]

hey joe i sent you a private message regaurding your 50 mm piston

[sho305]

That sounds right, long as piston height is same and stuff like that, you bore it to fit new piston, etc. The slight change in bore is not going to affect how it runs much because the displacement gain is fairly small. It might have a bit more torque, most gain will be from better cylinder ring sealing compared to old rings/cylinder. I don't know how big you can go before you run into cylinder thickness issues, most sites only list .25 and .5mm oversize....unless you can find a .75 for it.

[joefixit]

Well if my math and measurements are correct I will need to bore and hone a little more then .012 " and looking at the cyl. sleeve appears theres plenty of wall thickness. I toyed with the idea of a re-sleeve or possible cylinder plating but I think I will try the 75 mm piston should work out.. Thanks...... Later

[smallblock450sl]

Don't know of a 75 over piston (from Yamaha),maybe wesco? Maybe this will help in your desission. J38 and jn5's use the same crank and rod. J38 block and j38 head and j38 head gasket. Jn5 block and jn5 head and jn5 head gasket. I do not know if the dowel pins will line up on j38/jn5 head to block. J38 .50 piston-73.50mm (2.894). Jn5 std piston-74.96mm (2.953). If you think it can be bored to accept the jn5 std piston, use a jn5 head gasket and rework the head cumbustion chamber to match. It's just numbers, I have not tried this. Good luck on your project.

[kogieblack]

You can even get a 1.0. Email me if you have a problem sourcing it.

[sabercat]

i've also never seen a .75 over piston for the g9