Wayne.B wrote in
:

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?

Nope. The way to tell if the compression is good is expressed
by:

"Will it start?"

If it starts on all cylinders...compression is great!

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.

No valves. Intake ports and exhaust ports open as the piston
passes over them near BDC when the blower recharges the air and
blows out the dead gases. Piston rises cutting that off,
approaches TDC, cam rack in the head opens injection just as
compressed air reaches 1200F and KAPOW!, we're on our way down
again after this god-awful loud knocking noise also indicating
compression is great, making enginemen smile...(c;



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?

Worn rings, cracked cylinder head, cracked cylinder sleeve
usually starting at the port opening. Look at the exhaust. If
it starts steaming after it warms up, the head or block is
cracked allowing pressurized water into the cylinder, which turns
to steam on the hot piston. It always starts cold with white
smoke from incomplete combustion. 2-stroke DDs aren't
"environment friendly"....but owner friendly. Shrimp boats
running 4-53s may not have any rings at all and they're still
shrimping...(c;

You can tell when the rings are "too worn". It starts running
away when lube oil from the crankcase splashes past the worn
rings that are supposed to be wiping it off the cylinder walls
before the big bang....and the 2-stroker just runs away wild on
its own lube oil! Most exciting...black smoke for miles behind
boat...shutting down injection pump makes it go faster! Only way
to stop it is shut off its air supply by plugging up the intake,
which is very exciting on an engine that may explode in shrapnel
any second....(c;

But don't let that prospect bother you putting off that ring job
another year....

At least it'll never have a turbo-charger fire....

Aboard USS Everglades (AD-24), a nice old 6-71 powered a big DC
generator putting out 440VDC for the after gun turret from 1952
that had long since been removed for the stupid DASH helo deck.
(We were better off with the gun because at least it worked.)
The calibration laboratory I worked in needed a stable AC power
supply, even when the ship's AC was awful, so a DC to AC motor-
alternator set, 50KVA was installed and wired into the huge,
black bakelite DC power panel with the huge knife switches no
safety bureaucrat would ever approve of. (The lab actually ran
its lighting off a secondary 110VDC, NOISELESS, winding on the
genset.) The 6-71 drove the AC M-G set to 1800 RPM (60 Hz - 4
poles) any time we weren't parked against Pier Papa in
Charleston. (We used to turn back the speed on the M-G set to 50
Hz so the TV didn't wobble in the Med, under threats of "YOU FIX
IT IF YOU BREAK IT" from the Chief Electrician..(c; That 6-71
had over 12,000 hours on its meter on the panel and would almost
crank by hand! They are really great engines...

Oh, diesel fuel? No problemo. It sucked fuel oil from a 90,000
gallon tank.