Can a bad cam lower compression?

[jimjimmyjimjim]

I just rebuilt my 3.4l V6 Camaro. The block was checked and machined by a reputable shop and I put together the bearings, rings and pistons. The heads are rebuilt too. I installed an after market cam from Comp Cams. The compression in the 3 cylinders on one side is low - 90lbs. the other side is 140. I double checked the ring gaps and I made sure the heads were installed correctly. I set the valve lash the same on both sides of the motor.
The reason I rebuilt the motor in the first place was the low compression in those 3 cylinders. The only thing that hasn't been replaced is the cam from Comp. I put that in the motor before rebuilding it, put on the rebuilt heads and ran it for an hour or so, just long enough to break in the cam. When the motor wouldn't run right I checked the compression and the 3 cylinders were low. That's why I decided to rebuild the motor.

Is it possible that the cam could have been ground wrong and could that cause low compression?

[Superdave]

Possible but extremely rare. Are you sure the cam is correctly installed?

[SappySE107]

If it was installed wrong, both banks would still be equal. Do a leak down test and see if that comes up with anything. It would be very strange if one bank's cam lobes are worn more than the other side, and equally.

[jimjimmyjimjim]

I believe the cam was installed correctly. The shop installed the cam when they machined the block, I put the cam gear and chain on. The gear can only go on one way (same with the timing gear on the crank). I lined up the marks the way they are supposed to line up and I rotated the crank to make sure I wasn't off by a tooth.
The thing is, this is a donor motor. When I got it I put new heads on and the cam in (I didn't test the compression before I did this). When it didn't run right I did a compression test. The 3 cylinders on the driver's side were low so I had the head checked. There was no sign on the gasket of blow-by. when they said that it was bad I replaced it with a new rebuilt head, bolted it on and the 3 cylinders were still low. So, I tested for bad rings. The leak-down test showed a moderate leak in all 3 so I did a ring job. That's when I had the block completely gone through. I rebuilt it, bearings and all, making sure the ring gaps were right, etc. put it back together, put a DIFFERENT head on the driver's side, started it and it still ran wrong (won't idle). I checked for vacuum leaks and set the timing. Finally, I did a compression test and THE SAME 3 cylinders are low, just like before.
The only thing that I haven't changed that could possibly effect compression is the cam. I installed the heads on both sides in the same way, same gasket, same new bolts, same torgue pattern and settings. And I set the lash the same way on both sides, set #1 to TDC, tighten the rocker on the correct valves til 0 lash then 1/2 turn more, etc. The passenger side compression is fine, the driver side is not. I installed the rings the same way on all the pistons (which are also new). So, if I made a mistake during the rebuild how could the mistake only be on the one side and what are the chances that it caused the same problem as before? I can't figure out what is causing it.

[ForcedFirebird]

If the cam lobes were worn, it would be noticed by the amount of threads left after lash adjustment.

Have you checked the lifters? Take them out and see if you can compress them, but make sure they go back on the same lobe - the only thing not changed was cam and I didn't see mention of the lifter being replaced. Since the lifters stay with the lobe, this is the only connection I can see from before and after.

[jimjimmyjimjim]

If the cam lobes were worn, it would be noticed by the amount of threads left after lash adjustment.

Have you checked the lifters? Take them out and see if you can compress them, but make sure they go back on the same lobe - the only thing not changed was cam and I didn't see mention of the lifter being replaced. Since the lifters stay with the lobe, this is the only connection I can see from before and after.

I made sure I replaced the lifters in the same location. Comp Cam tech says that if the lifter is in the wrong location I would know in a very short time - "it would sound like someone with a hammer trying to get out of the motor."

What about push rod length? The same tech suggested measuring the length. If the length is out of wack the valves might not be closing all the way. Do you measure the pr length using the same method for stock rockers as for roller rockers?

[ForcedFirebird]

Same procedure. Well, then I would see if your lifters are sticking on the bad side of the engine. Since the rockers on the Gen1 engines, your lash will take up and slight variation in push rod size. I'd take them out and see if they are blocked and check your lifters as suggested before.