650 engine mods, advice needed

I dont know how much you can go with valve/piston clearance issues. IF your going thru all that work why dont you just put some bigger pistons in?

Larry C. Talked me out of taking any extra meat off of the head, and after listening to him, I agree. Most attempts to save cash result in spending even more!

Mark, now I understand about the rolling when the cam chain is tightened. Powerstrokefan, These mods cost no money as I have the parts (other than intakes which I have to replace anyway) and I have a buddy who will machine for free for me. Tomolu5, I haven't started the mill yet, just trying to get opinion from those of you who have been here before (such as yourself) and thanks for the advice. What was it that made you decide not to shave the head?

Thanks guys, I'm glad to be learning.

The reason I said and the Yoshimura pistons make plenty of compression.
Mark

Here's a cut out I did of the 650 and gpz port.

Intake's on the head.

Thats a serious size differance!

Mellvis, if I remember correctly your 650 is a D (SR) model, right?

If so it has a single roller cam chain which raises some issues:

- If you want to run a 750 cylinder block you need to make sure the block has the provisions for the cam chain idler sprocket shafts (marked red in the pic below), if it doesn't it won't work with a single roller cam chain setup.



- You also need to make sure that the cylinder head you decide to use has the 4 mount holes for the top cam chain idler sprocket (GPz 750 heads haven't got the mounts, so they won't work with a single roller cam chain setup).

Lastly, to fit a 750 cylinder block to an early (pre-81) 650 bottom end you will need to machine the upper case at the cylinder base (750 sleeves are too large to fit an early 650 case) = splitting the cases.

You can drill the four mounting holes for the idler sprocket in the GPz750 head, all the other 750s seem to have them pre-drilled.

Zukedave, thanks for the visual! I think you talked me into it.
So it's either use a 750 engine or bore the top case AND use the 750 cylinders and head? Yes, my bike is the d model but it has the 1978 B model engine, so it has the old style cam chain. I was going to use the old cam sprockets on the gpz cams, or so I think I can do that. If I remember right there was a discussion about the 750 using a larger wrist pin than the 650. If so, can the 650 rod be reamed to fit the 750 wrist pin, or will the 750 rod match the 650 crank journal? Also, is there enough material to just bore the cylinders to a 750 piston? Thanks again guys.

I think 650 and 750 rods are the same, and there is no room to bore a 650 liner to 750 size. You can however bore the 650 jug to accept the 750 liner.

750 Turbo uses a larger wrist pin, not the regular 750.

650 didn't get the HyVo style chain till 81 model.