120 to 150 is quite a difference between cylinders.  After you've verified lash and pushrod condition, take a closer look at the cylinders with the lowest compression.
Remember, the throttle should be wide open for the test and note the number of revolutions for each cylinder.  For instance, 150 psi taking 3 revolutions is not the same as 150psi taking 6 revolutions.  In a good engine, the pressure will be very close for each cylinder, and the number of revolutions will be the same.


Lawrenceville, GA

Compression tested  good,  120  to 150 psi .  I believe it must be valve lash or bent pushrods...I will check them all 

thanks

If the problem started with the removal and replacement of the valve cover, then start with checking the valve lash again.  Be sure to check both sides.  If other items were worked on while the cover was off, then look at those items also.  Beyond that, it’s back to basics.  A cranking compression test will eliminate most mechanical variables so that would be a good place to begin.

Lorena, Texas (South of Waco)

Valve Lash is recommended at .019 not .016.

  

Bryan, try the simple stuff first. Check the spark plug wires did not get disconnected or moved.

Hello, I need some help please. I have a stock 272 motor that was running great ...until I messed it up. Went to correct a leak on my valve cover and in my haste I installed the valve cover upside down ( aftermarket..no script)  
Started the motor and immediately heard the rockers hitting the cover. This result in dropping a push rod. Push rod was not bent and I got it tack in place. But the motor runs extremely rough. missing backfire etc. I checked that valve lash and everything is at .016".  

So my question is what should I check next?  Seems like the timing is off. I tried to adjust that but no fix yet.  

What damage is possible from the rockers hitting the covers?

I appreciate any advise


thank you

Bryan