[VFR750]

Tony

I can't imagine what's causing the slapping sound. 1/3 from TDC you get the sound, every 120 degrees of rotation?

If I think about it, 1/3 from 1 going to 6 is where 2&5 are getting very close to BTDC. They have not yet bottomed out, but are getting close to getting pushed upwards. 1&4 are really just starting to go down because the dwell at TDC as the crank journal reaches the "top" and has started to pull the piston down. 6&3 are halfway up. Could the rods be loose? Pistons loose in the bores?

I sketched the valve opening and closing on a circular graph and it would seem you are far away from valves getting close to the pistons. But maybe it's possible?

I have to ask, why didn't the other shops want to rebuild this engine? It seems very odd. And you've had some real misfortune with this build. Are you sure all of the parts were good to start with?


First, I'd pull the plugs and shine a bright led light into the plug holes and look into the intake and exhaust ports to see if the valves are getting too close to the piston. You should be able to see the piston top quite easily. Then rotate the crank in small increments and look in all ports, keeping notes of what you see. That should answer the question on clearance.