Compression question

[GrandMaster87]

What is a cranking compression reading for a fresh build 3.8 /stock heads .020 pistons and 206/206 cam.
Motor has not been fired yet. Seeing 100psi... seems low to me!
Thanks in advance
GrandMaster87

 

[muddin'metal]

It is low, but the rings have not set yet, it's really hard to say what the problem, if any, could be... A rather high psi variance from hole to hole would support a ring seating issue to some extent though

 

[GrandMaster87]

Compression issue

Thanks for the reply.
Guess I`ll look at the basics... might be the valves are to tight????
my machinist initially installed a timing chain tensioner but I was told that it was not needed on this build.
Thanks again
GrandMaster87

 

[charlief1]

If you're using forged pistons they need to warm up along with the engine. You need to do a compression test after you fire it up and it's warm.

 

[muddin'metal]

Valves?

Valve preload is a torque of 25ft lbs on stock shafts... but my experience with sbc says that too tight valves will cause loss of compression, but the sound of the motor turning over at start up is very strange... I'm still guessing it just needs to be heat cycled a time or two... a mis timed camshaft install can also cause crazy compression numbers... Good luck

 

[steve hughes]

If it's a hydraulic cam with new lifters the lifters won't be pumped up yet. That would probably cause the low # in addition to the rings not being seated yet.