I don't see how the o-rings alone would cause a compression loss. If the copper crush washer is bad, I'm sure the o-rings are going to be toast, though. I'm leaning toward starting with a leak down test before doing anything else. Then the next action will depend on the result of that. Does that sound sensible?

 

Easiest tests first are always sensible.

 

Jeb and I got the engine out today, and removed the right head. #7 cylinder (the one that showed low compression) has a distinct carbon buildup in spots on the piston and the head. The others had no carbon buildup, and what looked like a normal combustion pattern.

I'm going to try to post some pictures after my phone charges, but would like to know if low compression could cause the carbon buildup, or if it's more likely to be from a bad injector nozzle. Anyone have any ideas?

 

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I would say bad injector nozzle. 300psi isn't that bad and just bearly out of range with the others. I would of pulled the injector and GP before I would of pulled the motor, but that's me. How many miles on the motor? I think if I went that far if the miles are up I would just rebuild it anyway. Nows the time for mods if that's what you want.

 

We pulled injector and GP before starting. Injector looked normal to me, orings looked a heck of a lot better than mine did, with basically same miles on them. We double checked compression on that cylinder and a known good one ourselves, and the shop results panned out. We then got cylinder 7 to tdc, and blew compressed air into the cylinder. We heard nothing out the exhaust, but a lot of air hissing coming out of the crankcase. No bubbling though. We tried the same test on another good cylinder, with same results, but a little less air 'sound' coming out of the crankcase. The difference was there, but not much. Neither one of us was sure if we were doing this test correctly, but figured the next step was the head coming off, and figured it was probably rings. Some of the other reasons for pulling it were up pipe replacement and oil cooler rebuild. We didn't time it, but it probably took us 6-7 man hrs to get it out, so not too bad. I was shocked at how little rust was on this truck compared to my New England Plow Truck! The up pipe bolts even loosened and came out without a torch! My experience has now been exhausted, and I'm looking forward to seeing how a piston and rings gets changed out if that's what it comes too. Sorry Kevin, not trying to be excited about your misfortune.

 

I know it's hard to tell much from a picture, but here are a few. (Thanks for taking them when my phone died, Jeb.)

Here's the #7 piston with the carbon buildup. The 3 spots around the edge of the center lip are carbon, and the dome in the center has a pretty good coating, too. The cylinder wall is smooth, with no visible damage in the travel area of the rings.


One of the "normal" looking pistons . . .


And the cylinder head, with #7 to the left. There is a chunk of carbon to the left of the injector and glow plug ports, and it looks like a fair amount around the edges of the valves.


We're going to try to get a look at the valves and seats tomorrow to definitively confirm or rule out valve leaks.

 

The oil pan is still on so I'm just thinking out loud here, but if the piston cooling jet nozzle was broken off and the piston was overheating, could that cause the carbon deposits?

 

My bet is a leaking nozzle in that cylinder, injector.

 

That was my first thought, but I always tend to over analyze things.

 

Nice work so far. Please keep us posted...