TOPIC:

Hey guys. I am new to the board, but this site looks awesome! I have a quick question, if someone wouldn't mind answering it; i'll try to answer anyone else's that I can.

I have an 81 750 ltd that I am rebuilding right now. does anyone know how much I can take off of the head to bump up my compression? I am looking for a nominal increase, just something to give it a little extra zing. Thanks in advance!

Jason

Every head can be just a little bit different, but .020-.025 is normally fine, .030 is pushing it a little, and .035 is the ragged edge, this is for the 80-85 KZ and GPz 750 fours.

Does it go withoutsaying that the cams would need to be installed on slottd sprockets and degreed if you were to take .025-.035 off?

Or is .035 about the limit for cam timing not drastically changing and needing adjustable cam sprockets?

Being as the title of this thread is rather open, anyone want to clarify how little you can take off the head without changing much of anything, IE cam timing OR compression? I had the minimal taken off my head and block to true them back up, probably around .004-.005 each for lets say .010 total.

If any material is taken off the head or block the compression is going to increase and the cam timing is going to change, the only question is how much

If you want optimum performance, then you have to degree the cams any time the head/block is surfaced.

If your rebuilding it why not go with higher compression pistons instead of taking it off the head and messing messing with loosening the cam chain and the cam timing.
Mark

I thought about that, but the only high compression kit I found was with wiseco for something like $550 bucks! i like the bike, but I have too little $$ to take on that kind of expense. I can machine the head for free, so that was my best option.

Anybody have any idea how much I would have to degree the cams to compensate for say a .020" cut? I can't imagine I can do it by just moving a tooth on the sprocket in relation to the chain/crank. Thanks guys

Jason

$355.00 or so for the Wiseco 810 kit here in the US, plus whatever it costs you to have the cylinders bored.

When you mill the head or the cylinder block, you need to slot the cam sprocket mounting bolt holes in order to adjust the cam timing.
It can be done with a Dremel. it's just a little time consuming.