FOD ingestion damage - help?

I posted this in my build thread, but looking for some advice from a potentially wider audience.  A year ago, I managed 2.5 stages of Rally Colorado before my M42-equipped E30 swallowed an intake valve.  I acquired a replacement engine, tore it down and put it back together.  Had a machine shop rework the head.  Mostly left the bottom end alone.  Put it back together, ran it for less than 30 seconds, during which time it made an absolutely terrible noise.  Stuck a borescope in there and determined that it swallowed some metal.  As best as I can guess, it was some shrapnel from the first implosion that was hiding in the intake that I missed.  I found a very small chunk of what looked like valve seat.

The head looks probably salvageable with a valve job?  I figured I'd take it back to the machine shop and ask for help.

But what about the piston?  I'm super tempted to just grind it smooth and hope it's okay?  Is it at all plausible that if I do that I make it through the rally next month?  Or is it likely to just blow a hole in the piston on the first stage?

I'd just pull the engine and replace the piston for sure if I had more time, but there's no way I can do that before Rally Colorado.  On the other hand, spending $$$ and busting my ass to get there just to have it blow up as soon as I start is pretty dumb, too.  Advice sought.

Thanks.

If it doesn't impact the cylinder wall, I would run with it. I have torn apart several decent running engines that had a piston that looked like that.

Make sure there are no pieces that might break off the piston 

Thoughts about durability aside, the sharp edges from the damage to the crown might cause PI issues, so I understand the line of thinking in grinding them down. Just not sure it would make much of a difference and I don't know that I'd want to remove much material in addition to what's already missing. I've seen engines run with all kinds of crazy damage but personally I think I would do everything in my power to throw in another piston before the event since the head is off anyway. Not sure on an M42 car but I was able to drop the subframe enough to pull the oil pan on my E30 to replace rod bearings.

If it's not much of a sacrifice to lose the engine should the piston fail and destroy the block, crank, newly machined head, etc. then run it? My guess is the cost of travel, entry fees, and such would be a bigger loss...

I'd be worried about the ring land and if the ring is being squeezed. I just pulled apart a 7.3 powerstroke that had similar looking damage to the top of the piston and the ring dug a groove in the cylinder.

jgrewe said:

I'd be worried about the ring land and if the ring is being squeezed. I just pulled apart a 7.3 powerstroke that had similar looking damage to the top of the piston and the ring dug a groove in the cylinder.

Had that happen in my 22R Toyota 4x4 (ring land squeezed, no groove in the cylinder).  I worked broken pieces of the ring through the ring-groove to shave away material until it quit pinching, threw in a new (correctly gapped) ring, and ran it for many many more years.

Definitely not a rally car, but something to consider if a replacement cant be found quickly or cheap.

Don't remove material from the piston. I have peened down the high spots a few times with a similar failure and been successful. Hungary 's technique many times to clearance a pinched groove.  I would pop the piston up far enough to check the top ring and groove if at all possible.

TurnerX19 said:

Don't remove material from the piston.

Interesting.  My fear is that the sharp areas is (a) where cracks start, and (b) likely to induce pre-ignition.

The squeezed ringland is a possibility I hadn't considered.  The cylinder wall looks great now, but it's run so briefly I'm sure it wouldn't show yet.

Dropping the subframe to remove the oil pan so replace that piston is maybe a possibility.  Not sure if it's better or worse than just pulling the engine.  Pulling the engine now that I've removed the head is interesting--not entirely sure how to connect the hoist, now.  I actually just replaced the subframe, and I had a hell of a time getting it back together because the car is not exactly straight.

In reply to Berck :

I don't know about that engine specifically, but I pulled the headless block out of der Scheißwagen by putting the old head bolts in and lifting from a couple of those on each side.

Berck said:

Pulling the engine now that I've removed the head is interesting--not entirely sure how to connect the hoist, now.  I actually just replaced the subframe, and I had a hell of a time getting it back together because the car is not exactly straight.

I think I would just pull from the head bolts, or wrap a couple straps around the entire block in a way that won't slip. 

I have seen pistons that looked like a bomb went off in the chamber, and the engine was running just fine.  Pull the head because of an external leak or something, and it's the surface of the moon on the piston and the head's chamber.

The pits will fill with carbon in short order, I wouldn't worry about it.

And, now you know why it is really risky to reuse an intake manifold from an engine that suffered catastrophic failure.

In reply to Pete. (l33t FS) :

Now this is the kind of advice I was hoping to hear.  I bought a used piston and a new set of rings and am contemplating the possibility of replacing it in time.  But if I don't have to, even better.

To close out the thread:  It turns out the long pole in getting this back together is the head, so since I had plenty of time, I went ahead and replaced the piston.  I found a used set on eBay, put the good piston on the original rod with new rings and bearings.  It turns out you can replace the #1 piston in an M42 by only pulling the lower oil pan, which is super easy.

I'm glad I did, because the top piston ring groove was, in fact, smooshed.  The top ring was pressed in completely flush even after I pulled the piston, and also is compressed to the point that I can't even find the ring gap.  I'm guessing that means I'd have been limted to the second ring for compression, and not sure if that would have gotten me through a rally or not.

Still unclear if I'm going to make Rally Colorado; the machine shop said 3 of the valves are bent and they're not sure how soon they can get it back to me.