Oops, it expoded.

I just reinstalled some heads on a chevy 4.3 V6 in a 92 astro and after what seemed like ages, my buddy and I finally decided it was about time to start it. (no alcohol was involved [in the serious stages of the repair])
Only things not assembled was the front grill at this point. 2AM and we're cranking it, tweaking the distributor in case it was off to begin with, when we realized the fuel lines have been disconnected for a while, I stepped on the gas lightly and BAM the passenger side valve cover is spewing noxious smoke and the oil fill cap went airborne for 50'. (PCV valve tried it's best too)
I know the distributor wasn't that far from 0degrees. (unless it was somehow at 180)
When I worked on my Camaro's distributor and whatnot, I never had such strange occurrences.
Before I tear this thing apart to survey the damage, off the top of your head, what kind of damage am I going to be looking at and what situation would have caused this?
I'm stumped.

I just reinstalled some heads on a chevy 4.3 V6 in a 92 astro and after what seemed like ages, my buddy and I finally decided it was about time to start it. (no alcohol was involved [in the serious stages of the repair])
Only things not assembled was the front grill at this point. 2AM and we're cranking it, tweaking the distributor in case it was off to begin with, when we realized the fuel lines have been disconnected for a while, I stepped on the gas lightly and BAM the passenger side valve cover is spewing noxious smoke and the oil fill cap went airborne for 50'. (PCV valve tried it's best too)
I know the distributor wasn't that far from 0degrees. (unless it was somehow at 180)
When I worked on my Camaro's distributor and whatnot, I never had such strange occurrences.
Before I tear this thing apart to survey the damage, off the top of your head, what kind of damage am I going to be looking at and what situation would have caused this?
I'm stumped.

I would recheck your timing first and confirm that it is not 180 out.:banghead:

Everything important appears to be undamaged. I had a good look around with the valve covers off, then ran a compression test (which showed that I need to look at the rings some day, but it's not vital right now)
The valve covers looked like they've been through hell. I tried to fix the damage, they still don't fit right, though.

I'm well aware that the timing was probably 180 off. That's been rectified.
Brand new cylinder heads (valves, springs, etc.)
All new gaskets and whatnot of course.
Yet compression tests still show 100+psi.
My question remains: what in all engine physics could have caused it to have fired in such an odd location as under a valve cover? :confused:

You may have old spark plug wires that are 'leaking' spark energy. When this happens, you get almost-random sparking anywhere the wires run close to a ground, like the engine block or valve covers, etc.

If the valve cover itself was not well-grounded, the spark energy could have induced a spark internally, inside the valve cover area.

You may have old spark plug wires that are 'leaking' spark energy.
New wires and plugs, but I'll make sure to route them far from the covers this time. Thank you.

New wires and plugs, but I'll make sure to route them far from the covers this time. Thank you.

Good idea.

To expand on my earlier post, I think electrostatic induction (http://en.wikipedia.org/wiki/Electrostatic_induction) can cause problems. Although this may not be the most accurate term to describe the phenomenon, even new wires are subject to this.... which is why you should never use metal plug wire supports.

The first thing I thought of was that there was fuel leaking into the crankcase from the lines and lit up somehow. Is that what happened perhaps?

The first thing I thought of was that there was fuel leaking into the crankcase from the lines and lit up somehow. Is that what happened perhaps?
That was my assumption.

IMO the mystery is the source of the ignition

That was my assumption.

IMO the mystery is the source of the ignition

I'll try to have someone record video tomorrow when I start it again. If it occurs again (after I've been checking over EVERYTHING from the valves up) then I will post it for analysis.
Lets just hope that it was only a fluke and that it all starts up just fine. I have the battery charging overnight right now as the compression testing pretty much killed it.