Changed cylinder head, now no compression

[Tooonz]

…..other than compression lol.

If anyone has read my previous posts on my son’s jeep. We had a cracked head which led to coolant in the oil.
- I bought a remanned head, from a local shop that had been resurfaced, 3 angle valve job, pressure tested, completely redone. Cleaned the engine down, put the new gasket on,
Installed the new head, torqued it down per spec. Installed the rockers from the old head, assembled the whole rest of the engine, new plugs. Blah blah blah.
Turned it over to start, of course after putting fresh oil and fresh coolant in. And it spins over like it has no plugs in it at all. Checked compression and nothing in any of the 4 cylinders.

The head. casting I had was 117, the casting I bought is 403 in case that makes a difference.

I could understand one cylinder but not all 4.

 

[ColoJeep]

Check the valve adjustment. and do a air pressure cylinder leakdown test. That should point to the problem.

 

[Tooonz]

Check the valve adjustment. and do a air pressure cylinder leakdown test. That should point to the problem.

Okay i have to ask, how do you check valve adjustment? I didn’t see any adjustment on the valves.

 

[ColoJeep]

Okay i have to ask, how do you check valve adjustment? I didn’t see any adjustment on the valves.

These are a net zero preload system. They aren't adjustable like a 1st. Gen. classic small block Chevy. What has likely happen is the cylinder head has been resurfaced , decreasing the original distance between the rocker arm and the lifter. that distance difference is now trying to push the valve open. Additionally the valves may have been "deep seated " further into the head when the valve seats were machined. The difference between the original valve height and the new reground valve height is also trying to push the valve open.

These two factors end up pushing the valves open enough to bleed off cylinder pressure.
Changing the pushrod length is the way to correct this . Most automotive machinists would grind the end of the valve stem off the same amount the valves were sunk into the head. Most amateur mechanics overlook these issues.

 

[KennethS]

Changing the pushrod length is the way to correct this.

This is common with machined engine parts. The push rod length for the factory setup is not the same as what is needed after machining parts. A different push rod length is often needed.