I finally got back around to working on my 1981 300SD 126 after finishing "other" projects. Starts as soon as engine turns over. Very rough idle, smooth at about 2,000rpm. I have one cylinder (#2) not firing---so compression check on all cylinders (1 thru 5): 300psi, 60psi, 310psi, 310 psi, 330psi. Check #2 again just to make sure. 60psi. Not good. I do leakdown test---#2, set value at 30psi, leaks 95%. I apply 100 psi to listen for air---no air from intake or exhaust manifold---valves good---I do hear air from where chain comes out of crankcase---not good. Sounds like piston and or ring/s. 193,000 miles on engine. I'm trying to decide whether to take this engine apart and just replace the one piston/rings (maybe even use used piston/rings)---lots of work, but cheap----or go with a remanufactured short block at about 3K---or long block at about 6K. I would like to think "bad head gasket"----but just does not seem to fit test results. Only thing that bothers me is why would just ONE piston/rings "go bad"? You guys help me make up my mind! I will be making the 126 one of my daily drivers.

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K. Weimer
300SD (1)
300D (5) [Plus 1 parts]
300SEL 4.5 (2)
280SE (4)
280 (2)
250 (1)
250SE (1)
240D (7) [Plus 1 parts]
220D (11) [Plus 3 parts]
200D (2) [Plus 1 parts]
180c (with sunroof)

1995 Nissan UD1800 rollback
"If I can't fix it, it don't get fixed"

Ken on large industrial equipment diesels I have seen the top edge of the piston break off causing an "issue" with that cylinder. The only other things would be coolant or oil flow issues which resulted in the loss of same on that particular cylinder. I have some "spare" pistons for this engine if you need one although they do have some slight intake valve marks, some more than others. Let me know if you want to take a look at them.

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Jim