I have see 2 cases where a Diesel Was driving for a long time on Gasoline Diesel mix and it burned the tips off of the Injector Nozzles.

One of Vehicles in the above example was a Mercedes.

You might pull the Injector on what ever Cylinder you believe is noiser than the others and check the little protruding Pintle tip.

The pic is of a good stock Bosch Nozzle end. You see the Pintle in the Middle is OK and the central hole in the Pintel also looks good; nothing melted or deformed.
A Monark or Bosio Nozzle would have a thinner Pintle Sticking out with no hole in the center.

I pulled the injectors, and they've got a bit of tip left on each of them. They don't really match. There are two remanufactured injectors with slightly different nozzles, and three that might be original. New nozzles have slowly been working their way up the to-do list for this car...

But about the noise. It sounds exactly the same now that the injectors are removed (comparing hand cranking with injectors in vs. hand cranking with injectors out). The noise happens once per revolution of the crankshaft.

With your injectors removed, inspect the chamber that they screw into. (prechamber)

Send a good source of light into each of those chambers and you should see a ball of steel with 2 attachment points on each side 180 degrees from each other.

Try to look beyond this 'ball' to inspect the tip of the prechamber. Its possible that one of them exploded due to the gas mixture.

Gas burns hotter and is more volatile - faster explosions = more stress on the prechamber.

If you cant see, use some kind of flexible wire to poke around. I'll post a picture here so you can get an idea of how deep the wire should go.

prechamber

This is pressed into your head and rests under the injector.

Fuel is sprayed into this and exits the round tip via little holes as a fiery inferno.

http://www.peachparts.com/shopforum/...rechambers.jpg

If a piece of one of the prechamber tips breaks off, it will embed in the piston crown adn hit the cylinder head over and over again.


Try turning your cranksaft by hand with the injectors removed.

One of the glow plugs seems a little short when looking in through the prechamber, but other than that, the prechambers look intact.

Just did a compression test, and the results are pretty loopy. 300 320 390 320 280. My engine is much better in the middle, apparently. I redid the 390 a couple times.

Just realized I forgot to adjust the valves before the compression test - could be why the numbers were all over the map. Last adjustment was about 10k ago.

I would assume that this rules out any injector nozzle issues because the injectors aren't doing anything while the stop lever is pressed...

Right. I believe I've eliminated:
Injector issues (noise happens with crank without running and hand cranking without injectors)
Camshaft or Valve issues (nose happens once per crank revolution)
Belt-driven engine accessories (belt removal, inspection)
The fan (removed it)
Injection pump (injection pump cam turns 1/2 revolution per crank revolution)

That leaves:
The vacuum pump (driven off the back of the sprocket for the injection pump, but two lobes on that sprocket = one activation per crank revolution)
A piston or connecting rod problem. My least favorite option, but I'm pretty certain it's what I've got.