1983 300TD loud engine noise

[sethlong]

Greetings,

My 1983 300TD (OM617A) was accidentally run on approximately 50/50 gas/diesel for about 50 miles. Now it makes a loud noise, sounds a little like injector nailing but way louder, in time with engine RPM. Switching back to pure diesel didn't help (there may be some residual gas, but I did drain the fuel filter). The noise happens even holding down the stop lever and cranking it over, turning it over without it running. The sound seems to come from the front of the block somewhere - not sure where.

The engine sounds pretty normal except for the noise, and it even drives around the block ok, although I'm reluctant to drive it anywhere this way. I haven't run a compression test yet. Blowby doesn't seem to have increased. It still starts about like normal, so I doubt the compression has dramatically decreased. There was a lot of soot coming out the exhaust pipe while it was running on half gas. It ran rough with gas in the system, but with diesel it doesn't seem to shake any more than usual.

It's a rust-free car, and I've replaced all the suspension bushings and whatnot, so if the engine is toast, a new used one is a possibility. I used to have a good low-mileage OM617A with the wagon head in a rusted out car, but sold it - too bad.

Any speculation about what may be wrong would be appreciated.