Well its the motor in my sig.....brand new ZZ4 short block with brand new heads and GM headgaskets. Now I have been battling a ruff idle problem for some time and finallly pulled the plugs to do a compression test....all looked good....none were wet or too fouled but had some carbon deposits since I am still running a bit rich. But the results of the compression test were odd. Every cylinder EXPECT #6 had a dry reading of 180psi after about 3 hits on the needle. However #6 was only a 145psi.....did the test 3 times removing the hose and reinstalling it and testing other cylinders in between tests on 6 to be sure. So I pulled the valve cover and noticed both rockers were loose. removed the rockers and pushed down on the pushrods and the hydrolic lifters were hard. It burns no oil, consumes no antifreeze, no antifreeze in the or or oil in the antifreeze, and it doesnt overheat. Help? Can I just rotate the engine by hand till the number #6 exhaust is at the base circle of the cam (pushrod at lowest height) install the rocker nut to no lash and 1/2 turn and rotate the engine and do the intake? Then rerun the comp test and see????? What do you think it could be?

 

If the rocker arms were loose, then that means that the valves are remaining fully closed, which is when you get your highest reading from your compression test. If the valves were too tight...that would be a different story because that would mean that the valves were not sealing and you would get a bad reading.

Your rough idle could be a lot of things. What exactly do you mean by rough?? Choppy? Does it stall?? Is it just more lopey than you expected?

 

If you are running a bit rich...at idle especially, the idle will be rougher than normal. You do have a hot cam so it should be pretty lopey at Idle but not overboard. With carbs...you could make a LG4 peanut cam sound like a Hot Cam...if it's too rich.

 

If you're rockers were loose, then the intake could have been opening (more than likely it was) but not nearly as long (duration) or as high (lift) as the others. This will cause the pumping test to be lower because not as much air will fill they cylinder.

Do what you thought you should, then rotate the engine (either by starter or hand) a few full cycles and then check the lifters and pushrods. The lifters should feel "hard" because they're filled with oil. It takes a lot of muscle to push hard enough to get them to empty into the pushrod. They won't empty into the bore if the oil hole isn't lined up.

Anyway...... tighten them like you said, and try it again. If all works well, then put everything back together and fire it up. It should improve, but check it often.

Being who I am, I'd tighten them up, then use my dial indicator to make sure one of the lobes on the cam didn't get "whiped". It's odd that only one cylinder would do this on both the intake and exhaust.

Another thing I'd do is pull the valve spring and check for guide wear. If the engine's been running like that for a while, it's possible the valve put pressure against the guide from the rocker arm pushing it to the side.

Now that I think about it, check to make sure one or both of the springs isn't busted. I've had that happen before once, twice, or more than I care to admit.

What you want to do is up to you though. Do it right the first time, or do it again later.

 

One thing I forgot to mention that you should check.....

If you have press-in rocker studs, check to make sure they're not being pulled out.

 

screw in type

 

OK...... so what's the verdict?

Running like a raped ape yet?