964 camshaft seize Help?

[911 wide]

After performing a top end re build on my 964, it ran for one minute and the righthand camshaft seized and shredded the timing gear.
I have dismantled the complete engine and can only see the damage not the reason, it has broken two rockers but not damaged any valves or pistons.
When we assembled the engine the cams were oiled when installed, and the oil pressure was good when I started the engine.
I have checked the oil gallery and oil passage in the crank case, all clear.
I have contacted the engineer who made machine work and he assures me that all of the deck heights are correct.
I now have all of the parts to re assemble, but i am apprehensive as i cant find a reason.
Can anyone help

[Flat6pac]

If it runs, it usually tears up the oil pump drive and there is no way to see it so be prepared to open the case.
Bruce

[lucittm]

Did you use any assembly lube on the camshaft during the install? It should spin freely without the timing chain or any rockers installed, if not the cam tower is twisted. This is steel in aluminum so a coating of oil is very important to prevent seizing and just because you have engine oil pressure does not mean there is oil in the right hand cam tower.

If you want to be sure, leave the lower valve cover off for the initial cranking. There should be lots of oil coming from the cam lobe squirters and also from the sides of the cam journals. If not, don't start it and find the problem.

I'm with Bruce, I don't see how you could lose the teeth of the cam gear and not have aluminum shavings in the oil pump or not have the oil pump shaft broken or stripped.

You will know right away if you get no oil pressure during cranking.

You probably know all this. Tough break.

Good Luck,
Mark

[911 wide]

Thanks for your replies

When we initially built the top end the cams were lubed when installed and the cam was free before installing the rockers.
I have split the cases because of the debris.
Also striped and checked the oil pump which is ok.
When I told the engineer of the problem he suggested that the thrust washer had been fitted incorrectly, I am not sure that I agree with this? surely if the thrust washer came loose the cam would stop and not seize?

Any ideas greatly received