tmac

Hi, I recently replaced a blown head gasket and upon starting it again I found it to be running rough. After a compression test all are around 120psi except 1 and 3 have zero compression. Is there something I could have done to mess up the valves when I reinstalled the rockers and pushrods? I also put new plugs in so I will check them for oil. I assume if there was oil on them then I should assume bad rings. But would bad rings lead to absolute zero compression? Any help would be appreciated.

Thanks,
Taylor

hi im adam

It's really rare to get 0 psi..

Like you have a valve stuck wide open

hi im adam

I would pop off the valve cover and look at your lifter rods.

Turbo X_J

Was it the same before gasket replacement?

jebmccall

sounds like you have a stuck open valve or maybe you tore the headgasket reinstalling the head???

hi im adam

Bad/tore head gasket would still yield ~30psi

Unless you really messed it up.

tmac

Thankyou very much for your input. If I were to disconnect the fuel pump and plug boots then turn the engine over with the valve cover off do you thing I could check valve operation without splashing oil everywhere. I'm just curious because I was very careful with the installation. I'm thinking there may have been something I just never considered with the valve train. Torqued to 19ftlbs at tdc.

Thanks,
Taylor

tmac

I bought it with the head gasket issue and never ran it prior to "fixing it" because the battery cables needed to be redone. (the garage it was going to the JY so they took the battery out of it to keep and instead of just unscrewing the terminals they just cut the wires) When I head off none of the valves looked stuck open. Is this something that could happen the first time it turned over?

car5car

next time you remove head, turn it upside down and fill by ATF to check valves. Even if valves don't leak, it is still a good idea to lap them.

hi im adam

You can, but I would prefer to just spin the crank with a breaker bar.

You might have some oil spilling over.


1st thing I would do is make sure all the lifter rods are installed properly.

A valve will be held OPEN at all times if it is the problem. The cam pushes it open and lets it close. My guess is the valve is never closing, badly damaged, or a broken/bad cam.

The valve (s) could also never be opening and creating a vacuum and that would explain the 0 psi

Flipping the head and filling it with a fluid isn't a bad idea, but i would use gas and not stinky atf.

tmac

Thank you very much for the help guys! I'm in college so I can only go home on some weekends cause the jeep is back home. I took the valve cover off to find that several of the lifters have signs of failure. When I push down on the push rods there is some play in them as if somethings compressing. I looked this up and it correlates to collapsed lifters. I am concerned because there are several soft lifters that it might be a cam problem... Does this make sense at all? If I were to pull the head and then the lifters to find that they are collapsed would I still have to pull the cam to check it or could it be left and new lifters installed?

Thanks,
Taylor

Bustedback

You can put new lifters on an old cam, but never put old lifters on a new cam. If the engine has not been run a long period of time it is possible that the lifters lost their prime and not opening the valves. But you should still see some kind of compression, I would think.

Radi

If the lifters or cam were shot, the valves would not open, at least not fully. You have the opposite problem- no compression at all. That's likely a valve that does not close. A leakdown tester would be handy here.

Bustedback

BINGO! A leak down tester will answer a lot of questions as to where the problem is. Air from the crankcase means bad rings or a hole in the piston, air from the exhaust means a burnt valve or a valve that is stuck open, air from the intake means a burnt valve or a valve that is not sealing, air in the cooling system mean a bad head gasket or a cracked head or block.