I have recently rebuilt a bbc, 454, 76 motor with new just about everything but have a slight problem I have never experianced before. When rotaitng the motor by hand (huge bar on crank or in blower drive) the engine rotates evenly and freely. If you leave the engine stood then rotate it, it gets very tight - very tight, to the point where it stops rotating and I would normally asume there is a major mechanical defect. If you continue never the less (not my normal practice) it will free off and if you keep it rotating be free and even.
A few notes, on the problem -if there is one.
so tight it seems to be locked up and bar requires good heave but only on the initial rotation -1st valve spring compression.
had the lifters and rockers backed off and rotates freely
checked valves and chambers for seal after tight spot to see if valves bent - all ok and no issues there, clearances where all ok anyway.
rotates freely when moving
every time stood initial tight spot seems to be on valve spring compression but not in the same place. Dependes where stops and tightens up ridiculously on first spring compression phase of rotation.
also creaking heard on the tight spot -like a spring creak, but only on this first initial rotation.
valve springs are new and comp cams units matched to cam not particulaly high pressure - just above stock
never had an engine this tight, had some realy tight ones but this seems very unusual as the problem goes away on further rotation.
I have had the sugestion that this is newness, especialy of the valve springs, as all the clearances are correct and the problem is resolved on rotation I would be inclined to agree but realy don,t know and that,s the bit that bothers me, the not knowing bit.
any body any experiance to pass on, I have pulled this bloody thing apart on the top end twice now but will do it again if needed - thanks in advance and best wishes from the UK.
Simon
A few notes, on the problem -if there is one.
so tight it seems to be locked up and bar requires good heave but only on the initial rotation -1st valve spring compression.
had the lifters and rockers backed off and rotates freely
checked valves and chambers for seal after tight spot to see if valves bent - all ok and no issues there, clearances where all ok anyway.
rotates freely when moving
every time stood initial tight spot seems to be on valve spring compression but not in the same place. Dependes where stops and tightens up ridiculously on first spring compression phase of rotation.
also creaking heard on the tight spot -like a spring creak, but only on this first initial rotation.
valve springs are new and comp cams units matched to cam not particulaly high pressure - just above stock
never had an engine this tight, had some realy tight ones but this seems very unusual as the problem goes away on further rotation.
I have had the sugestion that this is newness, especialy of the valve springs, as all the clearances are correct and the problem is resolved on rotation I would be inclined to agree but realy don,t know and that,s the bit that bothers me, the not knowing bit.
any body any experiance to pass on, I have pulled this bloody thing apart on the top end twice now but will do it again if needed - thanks in advance and best wishes from the UK.
Simon