Anybody seen this happen before???

Got a call from a customer Sat afternoon telling me that the engine driving the air compressor on his rock drill had just blown the center part of the valve cover off. He said it made a fairely audible 'pop' when it happend and they immediately shut the engine down. The engine is a CAT 3054C which is basically a 4 cylinder CAT branded Perkins with a turbo, and the valve cover is a plastic composite of some kind.

I immediately suspeted the worst, that being a bent/stuck valve causing a pushrod to bend and get thrown, a broken rocker arm, etc, etc. Imagine my suprise when I got down to look at the machine and there was nothing wrong on the top end and the engine fired up and ran like a Swiss watch. We even went so far as to go ahead and load the compressor to make sure there was nothing wrong and beyond a bit of splash oil getting slobbered out of the broken valve cover everything was fine. There was no idication of the dip stick having moved from overpressurization of the crankcase, nor was the crankcase vent blocked in any way.

Now I could have understood the possibility of ether somehow getting into the crankcase, or gas vapors from flooding if it wasn't a diesel, and somehow getting ignited on startup. Thing is, it is a diesel, and this happened after they had been running and drilling for a good while. In other words there wasn't really any way for any kind of vapor to have gotten into the crankcase to ignite and even if it did what would have been the ignition source when everything is soaked in oil?

I've talked to a couple of other experienced mechanic friends since I got home yesterday evening and run this by them and so far we are all coming up empty as to a plausible cause for this to happen. The only thing the customer and I could think of would have been for someone to have stepped on it and cracked it, but where it's situated it would have been all but impossible for someone to have gotten their foot into that small of a space. Even then, if it were cracked, what would have made it go POP as forcibly as the customer said it did ???

Like I said myself and everyone I know are stumped and I'm just curious as to wether any of you guys had ever experienced anything like it. Especially as it pertains to a non-metal cover, and I say that because I know plastics can be stressed, etc, etc and snap with some force. There again this machine is somewhere around 6 or 7 years old so why wait until now to 'pop'??? Like I said nothing I, or anyone I know, can think of makes any sense at all as to why this happened.......... Any plausible ideas??????

Could something have broken or been thrown externally, struck the cover ,made the noise and broken it? Almost have to be if everything internally was in good shape...A puzzler!!

Plausible ???? If a piece of drilling equipment, or a chip of rock whizzed into it it could shatter. I have seen explosive de-construction on a 409 chevy with a bad fuel pump, and a bad PCV and a backfire.
It took all sheet metal off of it except little tabs where the bolts were. It also blew the hood off entirely. Jim

Friend of mine came home one evening to find the garage window broken. Knowing his son had a habit of tossing balls on the roof to catch them as they rolled back down, he asked Eddie if he knew what happened to the window. Eddie's reply was, "I dunno. Maybe a bird flew into it". Couple of days after it was replaced, it came up missing again. Bird must have flown into it again? Just a theory---

Does this engine have a draft tube to vent the crankcase or an PCV valve? If the pcv was clogged then crankcase pressure could build up and pop a valve cover. Similarly with a clogged draft tube.

I got a call to check out a ford f150 a few years ago, I believe it was around a 1995. There was a guy adding a propane system to the truck, he'd already added propane to several before this one and they all belonged to the same company. When he cranked it or tried to it backfired and busted the bottom out of the intake manifold which was made of plastic. It was still under warranty so to the dealer it went. Ford wouldn't fix it because of the propane set up and they said it needed a new engine. I was ask again to go check it out and surenuff it needed an engine.. The propane guy said it ran great when he pulled it in the shop to add the propane system, so did the guy that the truck was assigned to who drove this truck. All the pistons and cylinder walls looked like it had been burning sand instead of gasoline..

Thanks for the responses so far. The drill is John Henry drill which, in this case, is a drill boom mounted on a PC160 Komatsu excavator with a compressor setup taking the place of the counterweight on the rear. Because of this the compresor engine is setting a fair distance from the drill itself, even when drilling with the boom sucked in. Usually though the drilling is done with the boom setting about half extended just to keep as much flying debris from hitting the cab.

That said the engine is a diesel with an open draft tube straight off the top of the valve cover. It was not blocked, that was one of the first things I checked. There is no plausible way to hold pressure inside the engine in any way, shape, form, or fashion that I can come up with. Too the end of the draft tube is hanging in mid air and is located in an area where it wouldn't be accessible for someone to get to to manually block off.....especially with the engine running. Like I said the dipstick should have blown out before the valve cover went but it hadn't moved.

As far as something hitting it, the engine is located in an enclosed compartment located at the rear of the machine. The way it sits the majority of the part of the valve cover that broke is covered by a solid sheet of metal located about 3 inches above it. The metal sheet is rigid and can't move so there is no possibility that itshifted and did the damage. The rest is covered by the hatch which, again is solid but sets about 14 inches above it. The way the air to the aftercooler is piped across the part not covered at 3 inches leaves one spot less than 3 inshes wide for a foot, etc to hit it, and another spot maybe 5 inches long for something to hit it. Funny thing the exposed spots aren't where it broke. Beyond something flying up out of the hole, back 20 plus feet, and then reversing direction and heading forward into one of the cutouts on the housing, nothing can get inside. In other words a piece of rock big enough to do any damage is an impossibility.

So, good thinking so far based on just what info I gave
John Henry Drills

Crankcase explosions don't care if the engine is gas or diesel--makes absolutely no difference, as the oil vapors are just as volatile as any other fuel when mixed with air.

They are just like a gassing battery; all they need is an ignition source from "anywhere" to set 'em off.

The odds of all the rings walking around the piston and lining up at the gap at any one given time are very, very rare, but it does happen occasionally.

Last one I had blew all the external gaskets out and sounded like a cannon going off.

Allan