67 Firebird I recently bought has a 69 400 block running #18 Heads.
Compression is 180 PSI on 7 of 8 Cylinders. #1 Cylinder is 92PSI. Squirted some oil into the chamber and PSI stayed the same. Pressurized Cylinder when at TDC and air coming out of the Carb so figure #1 Intake Valve is leaking.
Going to pull valve covers and adjust / reset the lash on all the valves and see specifically if that helps #1 Cylinder.
Question: Before I dive in does anyone know if #18 heads had press in studs or adjustable? Did a look online and there are several ways to adjust lash but dependant on type of stud. i.e. torque to a specifc lb/ft or tighten till push rod just stops from being able to spin then go 1/2 turn more to same but use feeler gauge (car paperwork shows a Crane Cam saying set minimum .040" min clearance between the underside of the rocker arms and the top of the retainers after valve adjustment.) If that is the spec for the Cam I think I'm safe assuming they put in adjustable studs otherwise how would you go to a specific torque and still get 040" min clearance?
Those are 350 HO heads They have press in studs that were non adjustable. If you get a good set of lock nuts that are metal, you could adjust to zero lash and go another quarter turn like you would on every other hydraulic cam. The stock nuts are made to be torqued down and if you tried to do any sort of adjustment they would back off after a while. Those heads on a 400 would give you at least 10 to 1 compression which is way to much for today's garbage gas
Thanks. Will see once I pull valve covers. Will order set of locknuts and have on standby. I hear you on the compression those heads should provide. Previous owner ran regular pump gas and I have no idea how the motor didn't blow. Only thing I can think is the pistons are set low in the bore. Currently running 91 w/ Octane boost or 93 when I can get it. No noticeable pinging.
I have rebuilt engines where guys didn't hear any pinging and the bearing were down to the copper and the engine needed another crankshaft and set of rods.
