Topic: 1975 Honda CB750F Piston Valve Clearance

[RodSOHC750]

I installed modified 1979 DOHC pistons in my 1975 SOHC.  Reasoning for this is basically the cylinders needed to be bored and oversize pistons were not available unless you were ok with a comp ratio of 8.

I installed the pistons without rings and assembled top end using old gaskets and lightly tightened fasteners to test clearances. 

Intake Valve to Piston Clearance: 0.076 inch and occurs when Intake Valve lift is 0.032 inch on its way down.
Exhaust Valve to Piston Clearance:0.068 inch and occurs when Exhaust Valve lift is 0.025 inch on its way up. Total Exhaust Valve lift: 0.298 inch.

Are these clearances adequate? 

Other forum comments suggested 0.100 inch Exhaust and 0.080 inch Intake to be safe. 

 

[bwaller]

It can be reasonably safe to run as tight as 0.040" intake & 0.060" exhaust. As long as journal & rod brgs, small ends, pins etc. aren't worn out....

Usually though the tightest clearances will be found between 8 & 12 degrees crank position, (ATDC for intake valves & BTDC for exhaust valves) You'll need a correctly set degree wheel to be accurate.

[RodSOHC750]

I think I found minimum clearance by applying slight down pressure on the valve to hold it against the piston while slowly rotating the crankshaft and watching the dial indicator.