• Enter the March CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!

Top end rebuild on a 81 CB750C

John Luke

CB750 Enthusiast
Messages
55
Reaction score
0
Points
6
Location
Ashville
I’m rebuilding the top end on my 1981 CB750C it had a very small head gasket leak so while I’m already in the engine I decided to hone the cylinders and get new rings seeing as it’s low on compression. I’m gonna get the head and cylinders resurfaced to make sure the mating surfaces are flat. But the crankcase base gasket I can’t get resurfaced because the rods are sticking out and I don’t want to tear into it more than I have to. How would y’all best prep the base gasket surface? I used razor blades and a 120 roloc bristle disc. Then finished off with a free 600 grit Scotch-Brite. Any other ideas? To the touch it’s very smooth but I just wanted to ask to see if anyone had any ideas.

Thanks!


 
DON'T surface the head and top of block; you have too little room for that and the valves may hit pistons as well as the cam chain will run looser. Honda made no real allowance for that. I've never done it in a lot of engines too simply no need for it.

The leaks are from valves not the rings, they do it WAY before the rings ever leak.
 
Okay. Well currently when I put the head on the cylinder no gasket and I put a light on the other side I can see a little light. I’m not sure if the head flexes after you torque it down but I was worried that that could cause some problems.

Thanks!


 
That is NOT a flatness test, almost every engine on earth will do that. If they were that flat you wouldn't need a gasket at all ever.
 
Back
Top