Wayne,
K answered your questions very well, but I'm curious why you think you have
low compression, as that rarely happens on a detroit. I suspect an
underlying story here. Secondly, that engine has been made for 70 years,
there are many variations. Which one do you have? Please note there are many
different cylinder heads as well. The older ones are 2 valve and the modern
ones are 4 enhaust valves per cylinder. I think you should identify symtoms,
if you want meaningful help.
Steve

"Wayne.B" wrote in message
...
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?

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?

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