Crankshaft uneven when turning by hand

[DoctorEyebrows]

Hey all,

(1979 carburated 2000 engine)
I've recently done a head gasket replacement and head rebuild, and have just set up the timing. All of the pulleys are set to the correct marks, and the belt is installed. When I went to turn the crankshaft by hand to check everything is moving smoothly, the resistance on the crank is not even through a whole rotation. The crank should turn smoothly by my understanding, but there are sections of higher resistance. It is still possible to turn the crank through a full rotation (it doesn't bind anywhere).

The spark plugs are not installed, so compression should not be a problem here. The car was running fine before, aside from a coolant leak from the head gasket. I'm nervous to continue and start the car, as I don't want to inflict any damage.

Any thoughts on what could be causing this?

[davidbruce]

Is it bad in a particular spot or does it ebb and flow through a rotation? You are probably feeling the valve train resistance(friction and spring tension) of opening and closing the valves. Also If you have a mechanical fuel pump the resistance the lobe on the auxiliary shafts sees when the lobe opens/closes the pump. What was involved in the head rebuild? A valve grind will sink the valves deeper in the head and reduce cam to valve clearance. Did you check valve clearances after the head was torqued? Too tight and the resistance will probably be higher and may lead to increased cam/shim wear. Did you lube the cams on assembly? Presumably nothing was dropped ito an open cylinder. If your clearance is within spec and it ran fine before the head gasket replacement out are probably feeling the resistances generated by the timing belt. I would still rotate it by hand at least 2 full revolutions and double check that all timing marks are still correct.