Exploding Rocker Covers

[Brian Magee]

Has anyone experienced anything like this?

This car has done 40 miles and has a new 302 fitted with Ford Motorsport heads, Mallory dual point distributor, Holley carb and a fairly wild cam that I don't know the make or details of.

The owner took it out for a short drive and on the way home the engine started miss-firing. I trailered the car back to my workshop and after a compression test, attempted to start it. The engine would not start but would backfire which I suspect was due to a faulty condenser. I retarded the timing about 1 degree and had another go. The engine still backfired and then with an almighty bang, it exploded both rocker covers, sending half of one side into the ceiling of my workshop.
This engine has a dipstich in the sump as well as one in the timing cover. Both of these were ejected out of the engine.
I have checked the compressions and all are fine.

Any ideas?

Mystified Brian

 

[Bill D]

Did the valve covers have breathers, or some other means to prevent the crankcase from becoming pressurized?

Bill D

 

Once i saw something similar on a chevy where the mechanical fuel pump on the block was leaking fuel into the crankcase. It blew up when i was checking the spark, i guess it lit the fumes. My valve covers had a real nice dome shape after. The truck was pretty old at the time though.

 

[Brian Magee]

Bill D

One rocker cover has a breather to the air cleaner, the other has a rubbre bung that was also blown out.

Brian.

 

[Gordon Levy]

It sounds like the valve to piston clearance wasn't checked. I would bet that if you used a pretty agressive cam that is the problem. If there was contact, it bent a valve and broke the guide. Compression from the piston wnt past the guide and blow the valve cover off. You may want to check to make sure the cam was degree'd when it was put in. I have seen cams as far as 8 degrees off. This will also cause valve to piston issues.

[ March 27, 2003: Message edited by: Gordon Levy ]

 

Concerning the exploding valve cover, I would tend to agree with Eric. Been there, done that and have seen it more than once and it was always fuel and fuel vapors in the oil pan and valve covers. Some kind of leaks like maybe a stuck carb float or fuel pump diaphragm.
VIC

 

[Bill Bayard]

Brian,

What does the oilpan look like? If it took a hit as well, fuel in the crankcase would be my guess. Go find the dipstick and check the oil for gasoline.
Carbs can leak down, filling cylinders with gas, and if the car sits for a while, eventually gas will find it's way
past the rings, into the crankcase. This plays hell on cylinder walls(washing), etc.,and the resulting fumes have high explosive potential.
High pressure fuel pumps can easily waffle the guts of a Holley, causing leakdown. Is it a mechanical or electric pump? PSI?
Since you don't have to pull the rocker covers, turn the engine over slowly,with a breaker bar, and observe the movement and tightness of the valves, rockers, pushrods,
etc. Do another compression test. Hopefully, nothing but the valve covers will be a loss.
If that's the case, rebuild the carb, change the fuel pump and the oil. Then cross your fingers and try again. Keep us posted.
Good luck!

 

Brian,
Just a thought, I know you live very close to the old U.S.A.f. base at Greenham Common, are you sure you were not trying to replicate a crude type of cruise missile fired from a 302SB with those rocker covers.
Just a thought!!!

Ian

 

[Brian Magee]

Well I think I have worked out exactly what happened with all of your help (apart from Perrys). The day before the "Big Bang" I had attempted to start the engine. I had pumped the throttle a few times then turned it over. There was no sign of it firing so I flipped the choke on (no cable fitted yet). Still no sign of it firing so off with the choke and another try. A few more dabs of the throttle to no avail, then the battery started to die. I took the battery off and put it on charge. It was about 30 hours before the next attempt, the following day. In that time, all the fuel I had pumped into the engine had seeped through the rings into the sump. On the next attempt to start the engine, because the condenser was faulty a plug sparked with an inlet valve open and ignited fuel in the manifold. With petrol vapour coming from the sump up into the rocker covers and then through the breather to the air cleaner, this was ignited also which caused the rocker covers to part company from the engine at high speed.

Yesterday I took the carb off and placed a tray on top of the manifold, put the carb in it and re connected the fuel. I ran both pumps for about 30 seconds each then left it overnight. Next day there was no sign of any fuel in the tray so everything seems OK there.

Tomorrow I will change the oil, fit a new condenser and rocker covers, roll the car outside, put on a fire suit and crash helmet and give it another try.

I will let you know what happens.

Brian.

 

[Bill Bayard]

Brian,

Have you given any thought on a remote

starter switch for the second attempt?

I would have needed a change of underwear,

after the rocker cover blastoff!

Keep your fingers crossed!

Bill

 

I will be in my observation tower today complete with tin hat scanning the horizon to the west of London for that mushroom cloud in the sky, as Brian attempts to launch another rocker cover into orbit.
Brian if you would be so kind as to give me 15 minutes warning so that I can clear the streets of any old people,chlidren, and stray dogs.
Or better still how about 3 short blasts on the cars hooter !!!
Regards
Ian

 

[Brian Magee]

I delayed the firing till today to fool the enemy!

Change of condenser, change of oil, change of underwear and it fired first time. The new rocker covers are still intact.

Over and out

Brian.

 

[Dave Bilyk]

Just came across this post, which reminded me of something similar which happened to me many years ago. A friend had bought an Armstrong Siddeley straight six, which we picked up and brought home. On closer inspection, we noticed a plug lead was disconnected, so we reconnected it and started the engine. Immediately, there was a muted thud, followed by a whistling noise as the dipstick shot up into the air and disappeared into some adjacent woodland. Well we never did find that dipstick.
It turned out that the piston and rod was absent from that cylinder, so the spark had ignited the vapours in the sump.
Apparently it was sometimes possible to circumvent a failed big end, by removing the offending item downwards, only needing to remove the sump in engines of this type.
I also know of someone who lit a match to examine the inside of a Jag camshaft cover, and ended up with a blackened face for his trouble /ubbthreads/images/graemlins/grin.gif
I am always amused by these memories, but flying cam covers as well Brian, that's scary.

Dave

 

[Phil]

I can relate to this problem of fuel in the crankcase and oil pan, a few years ago a couple of friends of mine trying to start a Pontiac engine in very cold weather use a little too much ether...well when the motor finally "lit" it blew tho valve covers almost thru the bolts and the oil pan looked like an overstuffed garbage bag, this motor had a sheet metal cover on the lifter valley and it was pushed so hard against the bottom of the intake manifold that it looked like it came off a sheet metal press.
Carry on!
Phil