Javier97Z28

I want to check compression on my #6 cylinder to make sure nothing went wrong in there during the rocker flight, but I already have my intake manifold off.

Can this be done w/ the intake off? I assume it's no different than having the TB blades wide open right?

I know I have to put the rockers back on the slightly dead cam, but it'd only be to crank for compression.

Also, should I bother putting oil back in for just a compression test? Not sure if there'd be a point in that.. dont' think the oil pump really pushes any volume at crank...

Cmr0z28

Fuel would shoot all over the place. Maybe reconnect the rails without plugging in the injectors.

Javier97Z28

I meant the intake manifold off

The PCM fuse disconnected and coil wire removed will take care of any fuel pump or ignition firing.

96m6lt1

yes you can test the comp. that way,you are supposed to check by spinnin the engine over several times with the throttle wide open,so you cant get more open than that

Josh'95Z28conv

If you are checking just that one, and all the other cam lobes and lifters are ok, just put all other lifters, pushrods, rockers on, just leave #6 with nothing. That way the other cylinders wont build up compression over and over again, making it hard to crank. Since you're testing #6, its ok to leave the rockers off of that one. I wouldnt put lifters back on those lobes of the cam to check compression on the other cylinders though.

Another thing you can do with the cam out, or just all rockers off, is a leakdown test. Thats what I did when I did my cam swap.

cehan

I would absolutely not crank the engine without oil in the crankcase. You will incur some stress on your bearings without lubrication. The most wear on the bearings occur when you do a normal start to the vehicle, cranking the motor over, like when doing a compression test, without it starting will be hard enough on the bearings with just the minimal oil pressure developed by the starter cranking the motor over.

Josh'95Z28conv

Ive seen engines run quite a while without any oil pressure (pickup tubes installed incorrectly etc), and they had zero bearing wear (disassembled engines to make sure). Hell, my old 92 Ford F150 with a straight 6cyl I bought from my neighbor, who drove it two weeks to work and back with zero oil pressure. It did no major damage. It just had quite a bit of valvetrain noise untill it got oil to it. I replaced the oil pump and drove the hell out of it. Never had a problem.

Would I recommend driving with no oil pressure? No. Would it hurt if he cranked it for a few seconds for a compression test? Absolutely not.

cehan

What's the big deal about snugging up the pan with a few bolts and pouring 3 or 4 quarts of oil in the motor? In fact, if it was me and since the intake manifold is off anyway, I would pull the oil pump stub shaft and prime the engine with a priming tool while pulling it over by hand. The engine has been sitting for several weeks now and most, if not all, the oil that was trapped in the bearings has drained out so any cranking of the engine at all will be done with the bearings virtually dry. Why risk damaging the bearings to save 15-20 minutes time and $10? That makes no sense to me. You could even re-use the oil to save the $10 if you need to. If you don't have a priming tool, you can get one to use for free from Autozone. You pay them a deposit (I think it's about $25) and you get it back when you return the tool.

When I built my 383, I purposely left the intake manifold off until I had everything back together and was literally only a few hours away from starting it up before I installed it, just so I could prime the oil system one last time. But that's me, I'm just **** about details.

cehan

How can he check the compression on #6 without the rocker arms installed?

Javier97Z28

I'll throw some oil in it, wasn't about saving time or money, just necessity

LiENUS

Good, ignore everything josh said. Put ALL rockers lifters and pushrods on, including #6. If you have everything out already you could get by with leaving the lifters and pushrods off on everything but #6 if you pull the plugs. If you leave a lifter in without a proper pushrod and rocker youl'l ruin the lifter and the cam when the cam slaps the lifter. and you MUST have the valvetrain on #6 up and running to check compresson on it.

Josh'95Z28conv

I didnt say to turn it over with the lifters in the bores, and rockers off. I assumed he had them out.

I guess Ive never done a compression test with rockers off, so I dont know if there would be enough air in there to build compression. I do however know his cam lobe is messed up pretty good, and I wouldnt even assemble it for a compression test Telling him to do that is just stupid advice, period.

Honestly, Id just do a cylinder leakdown test if I were you

Oh, and a compression test without oil in the pan will hurt nothing!! Some of you guys arnt just ****, you're crazy ****. You're just cranking the engine over a few seconds for a compression test. Oil wont even get to the bearings in that time