400,000 miles on my 1980 300SD, idle got very rough, smooths out suddenly at about 2000 RPM. Cracked the fuel line to the #1 injector, made no difference. Cracked the line to #2 and engine died instantly.

Checked compression on #1, it was low, I think 90 lb, #2 was nice and high.
Assume I have either burned valves or cracked piston.

Looking for any advice and encouragement before I begin a long process of bending over the grill until by back fails. I do have a cherry picker to pull the head off.

Hidden bolts? Leave exhaust/intake attached to head for removal? Little expensive hoses and fittings on the underside I don't know about?

If it turns out to be a piston, what is involved in replacing just one? Can I pull the oil pan, unbolt the rod from the crank, and lift it out the top?

What evil pitfalls are lying in wait for me?

Thanks!

 

If the Valve adjustment does not help I would be thinking bad Head Gasket.

A Cylinder Leak Back test would determine where the leak is. You do not actually need to do the actual whole leak back test. Just hook up your Compression Test Adapter to some Filtered compressed air and listen and try to locate where that Cylinder is leaking.

Also is there any evidence in you Engine Coolant that there is a Head Gasket Leak?