955K precombustion chamber coolant leak?

I was doing some dirt work the other day and the machine was running great. I was about an hour into it when it seemed to start running a bit rough (almost felt like a miss). Temp was normal, oil pressure was great. I shut her down and started looking around and found some coolant on the top of the head next to the number two injector. Checked oil and coolant and everything looked OK (oil change only has a couple of hours on it). Waited a day and started her up. Ran fine. This sounds to me like the top O-ring on the #2 precombustion chamber sprung a leak that only shows when it gets up to operating temp. It may also be leaking some coolant into the cylinder when this happens, too. I'm figuring I need to replace those seals before running the engine much. Does this sound right to you folks? Thanks!

There is no reason to assume that the leak at top of the chamber means there is coolant getting into the cylinder. In fact i would say the miss and the leak are most likely unrelated.

If you had a leak into a cylinder through a PC chamber, you would have compression gas getting into cooling system when the engine is running. When engine is stopped, then coolant could leak into cylinder and might result in a hydraulic lock when it was cranked the next time or it might just wind up in the oil pan under the oil. Might be worth checking by loosening the drain plug after it has sat overnight, but if it was staying cool etc the last time you ran it, that scenario doesn't seem likely.

If it does not have coolant in the oil or compression leaking into the cooling system, I would run it at an idle and loosen each injector line in turn and localize the miss to a cylinder. You are looking for the one that affects the engine the least when you cut it out by loosening the line. Cover the connection with a rag when you loosen it to control fuel spraying everywhere.

Once you know which one it is, you can do some further diagnostics by swapping injectors and see if the miss follows the injector (bad injector) or stays with the cylinder (cylinder problem or fuel injection problem). Or maybe get injectors checked or replace them all if they are cheap enough. Mark each injector with the cylinder number so you can correlate your findings back to the original misfire.

For the leaking chamber, I would get the PC chamber removal tool or the complete tool set if yours has the two piece chamber + retainer assembly. Drain the cooling system and remove retainer or whole chamber if a one piece chamber and replace o-rings and copper seal washer. I believe all chambers are torqued into the head at 200 foot pounds, and they are frequently a trial to get them out. Can damage threads in head if they don't break free, so I don't remove chambers unless I have good reason. The old 2 piece style can be resealed by removing just the retainer and replacing those two o-rings. New style one piece must be removed and copper washer and o-ring both replaced.

Glowplug equipped engines will have one piece chambers and must tighten into the head with the Glowplug stopping in a specified quadrant to avoid interference with the fuel injection lines. There are different thicknesses of copper sealing washers to adjust the position. A copper based anti-seize compound can be applied to the threads and the washer before assembly to prevent damage the next time a chamber must be removed.

Good luck!

I had been running on a steep hill, and the fuel apparently sloshed around enough to wash some crud and water into the fuel line. Anyway, it's running good now and so the only problem is the leak. I've ordered a tool for removing the precombustion chamber, and I've also ordered new seals. I'll drain the coolant and pull the precombustion chamber when the tool gets here--and see if the chamber has any bad pitting, rust, or cracks. If not, I'll put new seals on it and reassemble.

Thank you for your very thorough response! I really appreciate your help, and I'm glad that this problem doesn't look too hard to fix.

Thanks again for all your help!