Cummins NHC 250 with dead cylinder...need some experts on the old engines

Hello everyone, I've been asking questions about the engine on my '69 White already, but I thought that I should start a new thread now that I've gotten into the engine a bit.

The truck hadn't run in almost 2 years. the engine is a Cummins NHC 250.

I was driving the truck home from where I purchased it, when, at the top of the first long hill, I lost power, the engine developed a miss, and the blowby coming out the crankcase breather increased drastically. I drove the truck home the last 30 miles and the problem did not get any worse.

There are no strange mechanical noises coming from the engine...just a dead miss on #1 cylinder as verified by an infrared thermometer on the exhaust manifold. One cylinder was weak before the miss developed...I could hear the unevenness when the engine was cranking over.

The blowby out the crankcase breather is a steady stream, not a "puff puff"

I pulled the valve cover and jake off the first head, and everything looks normal. All the pushrods are straight and in place. All rocker arms and valve springs are intact. The injector hold-down plate and bolts are intact and in place. With the engine running there is a "puff puff" out the head somewhere...it is difficult to tell where, but it seemed more like it was coming out of the pushrod gallery than out the injector.

Is it possible for that much compression to escape from an injector that is in place?

Is there anything that I SHOULD NOT do when it comes to removing cylinder head. Are there any tricks I should know?

Thanks for your help and experience.

Cheers,
Phil

 

So I'm assuming that I should order a set of head bolts, too. I once had a VW diesel back together after a ring job, doing the final torquing on the last head bolt and "snap". Off came the head, a $100 gasket, and new bolts later...

 

Hi everyone, I got into my old cummins, and this is what I found.

Piston #1 shows signs of foreign object damage, and it is also severely eroded. It is sloppy in the bore, and one place on the edge is eroded right down to the piston rings. The cylinder is not scored, but there is some melted aluminum from the piston stuck to the wall which chips off easily enough.

Piston #2 is tight in the bore and not eroded, but it does show damage from (I guess) foreign objects.

The cylinder head is undamaged and clean...everything looks great. So the question is this...what caused the erosion on piston #1.

The oil bath air filter had no oil in it, so the engine likely spent many hours ingesting something. I can't think that it ate too much dust, as the cylinders are not scored, and the bearings seem to be in good condition judging by the oil pressure. But the marks on the pistons cannot really be from anything but sticks or leaves or something that was hard enough to mark the pistons but not hard enough to mark the cylinder head.

Could a bad injector cause the overheating and erosion on piston #1, or did it just eat more stuff because it was at the end of the intake manifold and would have gotten more of the objects in the intake stream than piston #2. Of course, by that logic piston #6 should be the worst because the main intake air pipe from the air cleaner joins onto the manifold about over cylinder #5, so those two holes should have gotten more FOD than the ones at the front.

What have y'all seen. Thanks for the info.

Cheers,
Phil