Hey all, got a 3.8 back from the machine shop installed and I have compression sitting in the 20's. Looking for anyone that has experience with this for guidance.
Completely rebuilt and full valve job.

Timing? Valve train issues? Wrong lifters?? Valves adjusted too tight??

These are the possibilities I've heard. Any direction to go would be appreciated.

 

Stock cam and stock rockers? Only other thing I could think of is the cam is not timed correctly. If that is the case be glad it is a non interference engine unlike a Pentastar. Take #1 cylinder side vavle cover off and rotate crank the way engine runs to TDC by the marks and as you come up to TDC you should have the exhaust valve closed and see the intake valve close as you leave BDC coming up to TDC. That will verify cam timing in relation to the crank. Do this with plugs out so as not to fight the compression.
Or if you have an air fitting that goes in the spark plug hole then take #1 cylinder to firing stroke TDC and put 120lbs of air on it. Fill cylinder and halt airflow and it should hold for at least 20 seconds.

 

Yes, all engine parts are stock.

I'm thinking the timing is off as well, but I'm reading the 3.8 is an interference engine and the valves/pushrods will be damaged now...

Can you confirm?

It spins over with no extra noise.

 

If it’s an interference engine then if the timing is off enough then you would have issues. I’m not sure if a slightly off time job would avoid interference.

Did you assemble the block or did the machine shop?

If the piston rings weren’t offset from one another then that would also cause a lack of compression.