Loud Pop when rotating crank

[1987 Porsche]

So, I just installed all my rockers on cylinders 2,3,5 and 6. One and four were already installed when I did cam timing. As I was rotating the crank I heard a loud pop sound as if a valve spring came under pressure and released. I stopped the rotation and I immediately checked to see if all the adjustment screws on the rockers were fully backed out and some could be adjusted out a little more. When this happened the crank did not get any tighter as if something was binding. I looked at all the valve springs and valves (through intake and exhaust ports) and everything seems ok. I adjusted each valve to spec and the crank turns over fine, no noise. Multiple revolutions were done and all seems good. Whats your thoughts? The cylinders were refinished with new valves and springs. Is there any other checks I can do to ensure I didn't break a spring or bend a valve or something else? Could possilby the noise be the spring seating in place since this was the first time it was under pressure?

Thanks,

Lou

[bpu699]

Stuck valve that popped back in?

Broken valve spring?

[dannobee]

It could have been one of the lower valve spring seats "falling" into place.

[Mark Henry]

Was the sprocket tightened down? the valve springs can spin a loose cam violently.

[Catorce]

Are you sure both cams are in phase? When one of them is installed 180 degrees out, you get a pop when you turn the crank because both sets of springs are working then releasing at the same time. Remote possibility, but you should check.

[Trackrash]

Who did the heads? Perhaps a retainer was not fully seated? Time to carefully check your springs, retainers and valve keepers.

[1987 Porsche]

The sprocket was tightened to spec and the cams are in phase. The guy who rebuilt the cylinder heads is very well respected on this forum. Trackrash- Is there any checks I can do while everything is together for the springs, retainers, and keepers. At this point the crank has been rotated many times and no noise has occurred and it spins like it always has.

Thanks for the replies.

[Trackrash]

You should be able to see if the springs, retainers and keepers are good just by looking.

[1987 Porsche]

Ok. Thanks

[911pcars]

Rule one. If in your control, try not to assume anything is “right” until you confirm personally. People are human and mistakes can happen. The more QC checks, the higher the confidence the vehicle won’t fall out of the sky, fail to float, or stop working.

S