On Tue, 24 Jan 2006 19:50:34 -0500, "Eisboch" wrote:

Are your 671s turboed or normally aspirated?

Naturally aspirated.

It's funny when you get to
know how the various engines sound. I can identify the sound of those 671s
anytime I hear them start up.

You and all of my neighbors. :-)

It's like having a pair of Greyhound busses idling in your backyard.

A friend has a pair of normally aspirated 671s in a 1972 Hat 38 - actually
a conversion from original gas engines. They have over close to 10,000
hours on them and run like a top. Great engines.

They have a reputation of lasting almost forever and can be totally
rebuilt in place with new cylinder sleeves, bearings, pistons, etc.

It's my understanding that in commercial generator service they
frequently go 20,000 hours between overhauls although 4 or 5,000 hours
is more typical for marine service.

On Tue, 24 Jan 2006 18:59:06 -0600, dazed and confuzzed
wrote:

look for a leak in
your supply lines.

Any advice on how to do that?

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.

"Wayne.B" wrote in message
news
On Tue, 24 Jan 2006 18:59:06 -0600, dazed and confuzzed
wrote:

look for a leak in
your supply lines.

Any advice on how to do that?



Thinking about it, why not just fire up the hard starting engine then, using
a small container of fuel and an acid brush or similar, lightly wet each
fitting on the fuel lines from your Racors forward to the last fitting you
can get to on the engine. Watch for *suction*. Sort of the opposite of a
pressure bubble test for leaks. I don't know if this would work, but it
might. Or, talk to someone who, unlike me, knows what he is talking about.
:-)

It seems logical though that if that engine is otherwise running fine, you
are getting your RPMs and you are not producing smoke more than the other
engine, that a compression problem due to rings or valves is not likely.

Eisboch

On Tue, 24 Jan 2006 20:50:45 -0500, "Eisboch" wrote:

It seems logical though that if that engine is otherwise running fine, you
are getting your RPMs and you are not producing smoke more than the other
engine, that a compression problem due to rings or valves is not likely.

That would be the better out come for sure.

On Tue, 24 Jan 2006 20:34:46 -0500, Larry wrote:

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.

That's what I thought but everyone else says there are exhaust valves
in the head.

Wayne.B wrote:
On Tue, 24 Jan 2006 20:34:46 -0500, Larry wrote:


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.


That's what I thought but everyone else says there are exhaust valves
in the head.

There are valves.
Check:
http://www.yachtsurvey.com/comparing_diesel_types.htm

Courtesy of Detroit diesel!

Gaz

Gary wrote in news:C1EBf.325410$2k.236563@pd7tw1no:

There are valves.
Check:
http://www.yachtsurvey.com/comparing_diesel_types.htm

Courtesy of Detroit diesel!



He's right....Sorry.

Wow!! This goes on and on.

As most everyone has said the most likely culprit is fuel system related.
In my experience air leaks are very rare except when the engines have been
recently serviced. If this started after servicing the fuel filters an air
leak is very probable.

Injector tips are another possibility. BTW, injector timing is critical to
a DDA running well. You should probably invest the few dollars for a timing
gage. If you own the engines for a while you'll need one.

These engines are so simple and easy to work on that you would do well to
take a course on them. You could learn everything you'd ever need to know
in about a 40 hour course. That would include a complete teardown and
reassembly phase with a tune up. IMO, these are wonderful engines for the
DIY inclined owner.

Butch
"Larry" wrote in message
...
Gary wrote in
news:C1EBf.325410$2k.236563@pd7tw1no:

There are valves.
Check:
http://www.yachtsurvey.com/comparing_diesel_types.htm

Courtesy of Detroit diesel!



He's right....Sorry.

Wayne,

The only way to check the compression is by removing the injector,
their are special tools for this. It's not a difficult job, but you do
have to reset the rack, which can be a little difficult if you've never
done it before and don't have the tools for it. By the way, two cycle
Detroit Diesel's have exhaust valves in the head (usually four valves)
and an intake port cut into the side of the cylinder (no intake
valves). The blower builds pressure in the intake manifold and when the
intake port is open that pressure, along with the open exhaust valves,
is what forces the exhause out.