Valve cover gasket explosion:

[Erik Morris]

I'm surprised you had 30 psi oil pressure with the rocker shaft upside down, that's a lot of open area for pressure to be lost.

Amazed here as well, uncertain how anyone with a Service Manual could have reversed the shaft. That said.....I suppose there are lots of backyard mechanic folks without one. I'll admit mine is 23 years old and starting to fall apart at the binding, right through Chapter 8.

 

[PRHeads]

If the rocker shaft is upside down on the drivers side, you could easily have a stuck valve, which would explain the zero compression.
Could have bent a pushrod as a result, and then it falls out and is laying in the valley.

Easy enough to verify without pulling the motor.

Edit- Looking at the pic again, it appears plenty of oil was getting out to the valve end of the rocker...... so it’s probably not a lack of oil situation.
I’d still pull the drivers side valve cover before pulling the engine.

 

[Erik Morris]

If you haven't already, pull the drivers side valve cover, and take a look.

Drivers side valve cover removed, valve cover gasket in good condition for its age, rocker shaft is installed upside down just like the passenger side.

 

[Erik Morris]

Have you pulled the dipstick and smelled your NEW oil??? If it smells like gas, quack quack

Oil was drained this morning and did not demonstrate any signs of a fuel mix...no gas smell either.

 

[33 IMP]

Pull the coil wire, crank it over and watch the valves on cylinder #5.

 

[Old Sparky]

1971 383 brought to life after a 20+ year snooze. Engine has been idled for a max of 10 minutes across the past few days; 1 minute here, 2 minutes there.... oil pressure in the low 30s. Has started right up each time previously.
Ran the motor for 1 minute today, verified some gauges, shut off. Attempted a restart 10 minutes later and the right side valve cover gasket blew out explosively...sounded like a shotgun went off in the garage. Valve cover is physically bowed out from the pressure. Wife ran to garage to see if she was finally going to get some life insurance money.... is not impressed with my garage shenanigans. Removed valve cover gasket is (minimum) 20+ years old and in shabby condition. Oil breather is NOT clogged, flows freely. See pics.
Anybody ever experienced something like this? Valve cover is removed. Anything I should be checking/eyeballing before I throw new gaskets on and try another start?
View attachment 1246361 View attachment 1246362

Mine did the same thing....common problem with old cork gaskets.
The bang came from gas fumes in the crankcase.....don't keep starting and stopping after a few minutes , warm it right up or not at all.

 

[mike daugharty]

1971 383 brought to life after a 20+ year snooze. Engine has been idled for a max of 10 minutes across the past few days; 1 minute here, 2 minutes there.... oil pressure in the low 30s. Has started right up each time previously.
Ran the motor for 1 minute today, verified some gauges, shut off. Attempted a restart 10 minutes later and the right side valve cover gasket blew out explosively...sounded like a shotgun went off in the garage. Valve cover is physically bowed out from the pressure. Wife ran to garage to see if she was finally going to get some life insurance money.... is not impressed with my garage shenanigans. Removed valve cover gasket is (minimum) 20+ years old and in shabby condition. Oil breather is NOT clogged, flows freely. See pics.
Anybody ever experienced something like this? Valve cover is removed. Anything I should be checking/eyeballing before I throw new gaskets on and try another start?
View attachment 1246361 View attachment 1246362

fuel pump

 

[Erik Morris]

fuel pump

New fuel pump, pulls gas properly from tank, no leaks. Found a holed # 5 piston upon disassembly.

 

[33 IMP]

New fuel pump, pulls gas properly from tank, no leaks. Found a holed # 5 piston upon disassembly.

That'll do it!
Any idea what kind of piston? Cast? Forged? Flattops, how far down in the hole?

 

[Fran Blacker]

Well that sucks.

 

[MoparLeo]

A hole in the piston is how the fumes got in the crankcase.
Mystery solved but not the problem of how you got a hole in the piston.

 

[Erik Morris]

Mystery solved. Thanks to all who made suggestions and/or offered guidance. Engine disassembled, numerous broken rings, crank and cam in great shape, but...... The guilty verdict goes to piston # 5 which was holed to the tune of 2 rings deep....piston side between the damaged rings literally fell out. Valley pan gasket was pretty mangled as well as the aforementioned valve cover. Machine shop gets it next.

 

[Erik Morris]

A hole in the piston is how the fumes got in the crankcase.
Mystery solved but not the problem of how you got a hole in the piston.

Concur. Gent who sold it to me said "it ran when he parked it".... but that was 25 years ago.

 

[MoparLeo]

Or it ran before he parked it ...

 

[Erik Morris]

Or it ran before he parked it ...

 

[Erik Morris]

That'll do it!
Any idea what kind of piston? Cast? Forged? Flattops, how far down in the hole?

Stock factory original flat top pistons. Engine has never been bored.

 

[zyzzyx]

Call Arias for pistons. They will make pistons any size for you. If your block cleans up/Hones out
to +0.010 over, they'll make em! You don't have to go +0.030.