Replaced head gasket Now low compression.

[Barnon]

I just replaced the head gasket on a 8 month old rebuilt 4.0 Cherokee motor. I believe it failed from an overheating problem. Engine ran fine before I did the repair. Had the head checked and surfaced. Clean the block to shiny metal with a 3M scotch bright pad. Did the 3 step spiral torque process to 110 in/lbs except on bolt no. 11 to 100 in/lbs. Head Gasket from Enginetech. Brought no. 1 pison to TDC on compression stroke and install rockers and push rods in exactly the same position. I did get the pivots mixed up and the brigdes got slightly bent when I removed them, but I straighted them out the best I could.
Engine tried to catch at the start of cranking but continued cranking does nothing. Got Spark, got fuel but have under 50 psi compression on cylinder 2, 3 and 4. Have about 100 on 1, 5 and 6.
I am not a master mechanic by any means. I just do what I read from the Haynes manual and Mitchell on Demand software. Any suggestions for what to do next would be greatly appriciated. I was going to take off the rockers and pressure test the cylinders to check if valves were seating correctly.
Thanks for any help.

[JDPascal]

Hi Barnon Welcome to AF

Your low compression on the 3 adjacent cylinders is suspicious and sounds like a possible head gasket/sealing problem

Checking the cylinders with compressed air is a good idea. When you pressure up the cylinders, leave the plugs out of the all the cylinders while you apply the air. That will tell you if there is cross cylinder problems. Of course you will listen at the intake manifold and the exhaust for the valve condition.

Double check your rocker install and make sure that the pushrods are seated correctly in the lifters otherwise the valve can be held open and may hit a piston and bend the valve.

Did you use new head bolts. Some of the 4L engines use head bolts that are only to be used once not sure if yours is that new.

good luck....and let us know what you find....

JD

[Barnon]

Got it working. Not sure what fixed it. I disconnected and reconnected a few connectors and it started right up. The guy where I got the rebuilt engine from said thats not uncommon to get low compression readings before it gets oiled up.

Thanks for the info. It's nice to have a place to ask questions.