What would have caused this?

[csb]

Car: 1997 528i. Overheated once, briefly, for prior owner. He replaced the thermostat, rad and coolant hose. Didn't overheat again. He drove it home one day and parked it. The next morning, he went to start the car and, as it was cranking..."Boom!". The valve cover literally exploded into pieces. The funny thing is that nothing in the valve train is loose/out of place. Cams/springs/chains...all in tact and installed. What could have caused this? A buildup of pressure? I'm about to dig into the motor to determine if it can be repaired in a cost-effective manner or if I should simply purchase/install a new engine. Thoughts? Ideas? Thanks in advance...Steve.

[fifthand]

Very strange. So you are saying the head/valve train is fine it is just the cover that went wacky? I would do a compression test at the least. Does the engine oil or coolant look funny?

[02Pilot]

Never heard that one before. The two things I would consider possibilities would be either a rapid build-up of pressure in the crankcase (though I'm not sure what could possibly generate such explosive pressure that quickly, nor can I believe that it wouldn't blow apart the CCV long before the valve cover) or one of the coil packs exploding.

The valve cover is not exactly the first thing I would expect to explode. I would very carefully inspect the coil packs, wiring, CCV, and anything nearby that could have contributed to pressure building up, leaked fuel, or produced a spark.

[mattmartindrift]

leaky fuel injector + non-sealing piston rings, possibly causing fuel vapors to build up in the crank case. Upon ignition, kaboom?

I find it hard to believe that a metal cover just exploded, seems crazy.

[fifthand]

leaky fuel injector + non-sealing piston rings, possibly causing fuel vapors to build up in the crank case. Upon ignition, kaboom?

I find it hard to believe that a metal cover just exploded, seems crazy.

Good enough theory. Are the I6 covers metal? I thought they were plastic.

[mattmartindrift]

Good enough theory. Are the I6 covers metal? I thought they were plastic.

possibly, i'm new to this stuff and i have a V8; so, I know they're metal.

[02Pilot]

leaky fuel injector + non-sealing piston rings, possibly causing fuel vapors to build up in the crank case. Upon ignition, kaboom?

I find it hard to believe that a metal cover just exploded, seems crazy.

It's an interesting thought, but you'd need enormous fuel dilution of the oil and a spark source inside the crankcase. The piston rings would have to be GONE for this to happen.

[mattmartindrift]

well it was overheated. if the head warped enough, there could have been a route other than piston rings.

I'm aware it's a long-shot answer, but exploding a valve cover is a pretty long-shot consequence of a problem(s)

[csb]

Thanks for all the replies, guys. Today, after removing bits and pieces of PLASTIC valve cover, I used the air compressor to make sure all was clean. Then, with the coils removed, I attempted to crank the engine. It turns over completely normally. I've ordered a used v.c...should be here Saturday. The dealer told me that it is fairly common for the rubber crankcase vent hose which goes from the v.c. to the crankcase ventilation valve to the dipstick to get clogged with "sludge". If this were to happen, crankcase pressure would have nowhere to go and "Boom!". So...I removed/inspected the top hose...it was scummy but not completely occluded...no idea about the rest of the ventilation system. My plan, at this point, is to test compression and then, once I've installed the new v.c., to attempt to start the engine (leaving the crankcase vent tube open to ensure ventilation). I'll cross my fingers at this point...

If the head warped, will it be worthwhile to remove it, have it checked/decked and install a new head gasket? There is a very reputable cylinder head specialty shop 10 minutes from my home. They charge only $85.00 to completely inspect/clean a cylinder head. Thoughts on this? Thx again...

[NY Bimmers]

A repair that makes me happy i have the 4.4......for once......

[Gumbi4u]

Post pics of the carnage. Lot of skeptics here including me.

[csb]

No pics...it's all cleaned up and the v.c. has been tossed. Just looks like a 2.8 I-6 with the v.c. removed. Skeptics be damned...I'm telling the God's honest.

[fifthand]

If the head warped, will it be worthwhile to remove it, have it checked/decked and install a new head gasket? There is a very reputable cylinder head specialty shop 10 minutes from my home. They charge only $85.00 to completely inspect/clean a cylinder head. Thoughts on this? Thx again...

I've always been of the opinion that if you go to the trouble of pulling off a head to simply rebuild it. If you're like me, you don't like to "redo" things.

[curt2128]

WHOA some mobester put a hit on you....





and the lackie didnt do the job right?

[csb]

Update: Did compression test today...only 1 of 6 cylinders read normally...all others b/w 0 and 90 lbs. Bought a new engine today...replacing the tranny at the same time even though there's nothing wrong w/ the existing tranny. Why? Lower/matching miles on both (from the same car).

[02Pilot]

I hope you'll pull the old engine apart and try to diagnose what happened. I'd really love to know what failed and how.

[cal45fan]

Defective CCV valve not opening to recirculate blowby gas into the intake manifold to be burned.

[fifthand]

Defective CCV valve not opening to recirculate blowby gas into the intake manifold to be burned.

Would that really blow out the rings that bad though? I would suspect the valves are "OK" and that the compression loss is primarily from the rings.

CSB,

Did you happen to squirt a bit of oil (as equal amount as possible) into the chamber and retest compression? Also, I hope you tested on a relatively warm engine.