Strange "detonation" in my 401 today

[iCEMAN]

Out wheeling some rocks and trails today with my local club. Stopped to do a repair on a guys driveshaft and when I restarted the jeep - BANG!!!

Smoke poured out from under the hood for about a minute and everything was quiet. Opened the hood slowly and discovered the 'smoke' was coming from my oil fill tube which was now missing the breather cap. Found the cap about 10' from the side of the Jeep. Upon further inspection, discovered that both valve covers had lifted on the inside (intake manifold side) about 1/4" and blown the rubber valve cover gasket out in chunks about 6-8" long.

Sat for about 10 minutes then said, what the hell, it is probably already blown, see if it turns over. Motor started on the first click of the key and idled perfectly. Drove it slowly to the parking lot and removed the valve covers. Pounded the bent edges back into place, installed a new set of gaskets and the truck ran perfectly the rest of the day wheeling (about 5 hours).

So my question to you motorheads is this:
What would cause a detonation in the valve covers hard enough to almost blow both covers off the jeep? Can't be something real serious or I would think the motor would not have run the rest of the day.

 

[CJ]

Seen it before... Gas / gas fumes got into the upper end and, sucked into the engine via a vacuum line hooked to a carb. The PCV system didn't evacuate the fumes and BOOM!

Might not be exactly what happened but - about the only way to blow as you did, is from gas....

Are you carbed or FI?

 

[iCEMAN]

Seen it before... Gas / gas fumes got into the upper end and, sucked into the engine via a vacuum line hooked to a carb. The PCV system didn't evacuate the fumes and BOOM!

Might not be exactly what happened but - about the only way to blow as you did, is from gas....

Are you carbed or FI?

Carb. Holley Truck Avenger. PVC valve never popped out of the manifold, but did a number on the valve covers!

 

[Thorwon]

Might want to check the oil in your engine for gas. I saw a the valve covers blown off of an engine and a nasty fire when a fuel pump filled the crank case full of gas. All we could figure out was it back fired and the flame went through the pcv hose into the valve cover and through the engine.

 

[iCEMAN]

Might want to check the oil in your engine for gas. I saw a the valve covers blown off of an engine and a nasty fire when a fuel pump filled the crank case full of gas. All we could figure out was it back fired and the flame went through the pcv hose into the valve cover and through the engine.

We did check the oil and it was still nice and thick like it always is, plus could not detect the smell of gas. Doesn't mean it was not there. Going to do a complete oil change this week anyway on it.
Also thinking of having the carb rebuilt just to be safe and double check the timing. (although it ran perfect afterwards just like before)

Myself, I had not seen the valve covers blow like that, so I thought I would ask. Thanks for the answers.

 

[Old Dog]

WOW, I've never seen that one before.

 

[2lostspace]

I have seen this once. It was on a 4cyl engine the vent on the engine got plugged and the internal gases in the block had no were to go. The valve cover and gasket was the weakest point.

This was the only experience that I have had with this type of thing.

 

[iCEMAN]

WOW, I've never seen that one before.

You should try it from the driver's seat! Makes the heart skip a beat or two for sure.

 

[kicknjeep]

X2 on never seeing that before
And I bet a change of shorts was in order as well....

 

[iCEMAN]

X2 on never seeing that before
And I bet a change of shorts was in order as well....

My daughter was with me riding shotgun. She looked over at me with a "WTF" look on her face. I just calmly got out trying to act like it was no big deal and looked under the hood.
She was cool with it since no one in the group got all excited. She did however, get out when I restarted it. Have to say, thought I would need a crowbar to pry my pucker off the seat though.

 

[kicknjeep]

So it actually built fuel vapor in valve train and detonated?. Well hope everything is still in working order, What can be done to avoid further actions like this?. Let us know how it goes.