Help! Right side cam timing? Or another issue?
 

Hi all,

I have a 1972 911T PMO carbs.

After a compression test:
the left side reads 120
The right side is stuck at 90.

I have chain tensioner upgrade to later tensioners. I used the stomski tools to make sure I have proper tension and valve timing… I went as far as to replace the tensioner. I’m still getting the same readings. Any thoughts?

Did you test all the cylinders on each bank?

Do a leak down test to eliminate the possibility of bad rings, or bent valves.

Could be cam timing, or the right side has more deck height than the left.

Can you see the base gaskets on each side? Has the motor been rebuilt?

The motor has been rebuilt over the course of a few years. It is a fresh motor. I had it running at one point, albeit poorly with the right side cam issue. It didn’t sound right so I pulled the spark plugs and found I wasn’t getting the proper compression on the right side. The car has been a slow moving project for me.

I did a leak down and that came out well, no leaks, so I’ve eliminated that as a potential issue.

The left side reads 118-120 psi on all cylinders. The right side is reading ~90 psi on the entire bank. This is after replacing the hydraulic tensioner after realizing there was an issue. I also used the stomski chain tensioner tool to put more tension on the chain to get it to 2.6mm on the valve and readjusted cam timing accordingly. I double checked the base gaskets with a camera and they are all there.

I’m truly stumped. I would think if it was the cam itself it wouldn’t be so consistent across the entire bank.

Any other ideas? How long does it take for oil to pump into the hydrolic tensioner to give it proper tension? Or, maybe it is the base gaskets? All ideas are welcome at this point.

If the cams are timed correctly, I would suspect that the deck heights are different.
However....is it possible that you have the cams swapped and installed on the wrong sides? Left cam on the right side and vice-versa? I would think this would result in compression issues, or worse, on both sides...but it's a thought.

regards,
al

Has this motor ran or is this an initial start up? Is it a stock motor?

If you have an aftermarket cam then they are usually timed differently then the stock cams. Contact the manufacturer for timing specs.

If timing is correct, and you don’t have any pressure leaks then it sounds like you got different deck heights.

It has 2.2 pistons but the cams were not changed.

I would consider this the initial startup as the car has been running, but not on the road since the rebuild. When it ran after the rebuild it ran at idle but if you revved it a bit it would die off. It was in rough time but the after removing the spark plugs they were really clean, no combustion.

Sounds like my deck heights could be off so I’ll give that a shot.

Help! Right side cam timing? Or another issue?
 

Could one cam be 180 off ?

Asking because I once had to re-do the work of a "reputable" German Porsche enginebuilder shop on a 3.0 Carrera engine.
They had installed the right camshaft 180 off + they had installed a 3.0 Turbo camshaft on that side as well.
That engine run but very bad AND that side had clean sparkplugs = no combustion.

This is easy to check, just remove upper cam covers and see/feel if both 1 and 4 cyl. has either closed or open intake valves at the same time.
If so then one cam is 180 degrees off.

Remove the upper cover and check cam timing.

Maybe a stuck valve? If it’s been sitting? ��

You should have primed the tensioners before install.