Wayne.B wrote:
Not having made any significant displays of ignorance lately that I
know of, thought I'd give it a try:

Is there any way to measure compression without removing injectors or
other major components on DD671s?

No not really & you need to use the correct tester of course, which can
be pricey it's probably better to just get a tech to test.

Second question:

Since the DD671 is a 2 cycle engine, I'm assuming there are no moving
valves, just fixed intake and exhaust ports in the cylinder walls.

Anyone know if that is correct?

No it still has an exhaust valve(s) in the head as usual. The air flow
is from;

the blower pressurised air box on the side through,

tangential inlet ports,(uncovered as the piston approaches BDC like the
2 stroke OBs),

incoming fresh air flows to help purge any remaining exhaust,

the rising piston rises covering the inlet ports, the exhaust valve
closes & compression up to fuel injection just before TDC,

The power stroke is till towards the bottom when the exhaust valve opens
& the exhaust starts to flow

It's certainly a "2" stroke but it has most of the elements of a 4 stroke.

This is why when I waaarr on endlessly about how bad 2 stroke OBs are,
I'm usually careful to say "crankcase transferred 2 strokes" your diesel
is not that. The crankcase is not "deliberately":-)) pressurised (not
that you'd guess it given the way they throw oil) & the design is very
successful.

If so, I'm also assuming that any loss of compression would have to be
from worn rings and/or cylinder bore. Also correct?

The bottom part of the engine is pretty much the same as a 4 stroke, wet
sump, pressure oiling etc so save some accident (air cleaner something
broke??) you shouldn't expect the piston/ring/bore area to fail out of
the blue. The usual suspects are always there, head, valves (exhaust
only but they still get burnt).

Your first instinct is probably the best a compression test; it should
tell you whats happening or least give you some good clues.

K