Detroit Diesel (DD671N) Questions
 

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?

Detroit Diesel (DD671N) Questions
 

Wayne,

First Caveat: I've never worked on any Detroit Diesel engine (that
I can remember)

Wayne.B wrote:

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

Don't know (shrug)

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.

There are exhaust valve/valves in each cylinder in a two-stroke
turbo-diesel. See http://auto.howstuffworks.com/diesel-two-stroke1.htm

Also see http://www.marineparts.com/partspages/DETROIT/DET12.HTM for a
list of exhaust valve part numbers including for the 671.

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

See above. Loss of compression could be due to rings/cylinder, exhaust
valve, etc.

Good luck with it.

Don W.

Detroit Diesel (DD671N) Questions
 

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

Detroit Diesel (DD671N) Questions
 

On Tue, 24 Jan 2006 22:40:54 GMT, Don W
wrote:

See above. Loss of compression could be due to rings/cylinder, exhaust
valve, etc.

Good luck with it.

Things are not at a critical state since they are both running well,
but the port side engine is taking a few seconds longer to cold start
than it used to, so I'm assuming that something is mildly amiss.

Detroit Diesel (DD671N) Questions
 

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?

Detroit Diesel (DD671N) Questions
 

On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi"
wrote:

I think you should identify symtoms,
if you want meaningful help.

It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt
within the last 1,000 hours or so by the previous owner.

My port side engine is taking longer to cold start than it used to,
sometimes needing 8 to 12 seconds of cranking. It used to start on
the first or second turn even when stone cold, and the starboard
engine still does. If it has been run within a day or two it still
starts very quickly. There is very little exhaust smoke at startup
even when cold, and what little there is goes away quickly. The
engine is running well and making full power as far as I can
determine.

Detroit Diesel (DD671N) Questions
 

"Wayne.B" wrote in message
...
On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi"
wrote:

I think you should identify symtoms,
if you want meaningful help.

It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt
within the last 1,000 hours or so by the previous owner.

My port side engine is taking longer to cold start than it used to,
sometimes needing 8 to 12 seconds of cranking. It used to start on
the first or second turn even when stone cold, and the starboard
engine still does. If it has been run within a day or two it still
starts very quickly. There is very little exhaust smoke at startup
even when cold, and what little there is goes away quickly. The
engine is running well and making full power as far as I can
determine.


There's a guy at our marina who had a somewhat similar problem for a couple
of years. Turns out he had a very small air leak in the fuel supply line
for one engine. It would run fine after starting, (I assume because the
leak was overcome by fuel, but that is pure speculation), but was hard
starting.

Ain't boats fun?

Eisboch (grandkid #5 is a girl!)

Detroit Diesel (DD671N) Questions
 

On Tue, 24 Jan 2006 19:17:09 -0500, "Eisboch" wrote:


"Wayne.B" wrote in message
.. .
On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi"
wrote:

I think you should identify symtoms,
if you want meaningful help.

It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt
within the last 1,000 hours or so by the previous owner.

My port side engine is taking longer to cold start than it used to,
sometimes needing 8 to 12 seconds of cranking. It used to start on
the first or second turn even when stone cold, and the starboard
engine still does. If it has been run within a day or two it still
starts very quickly. There is very little exhaust smoke at startup
even when cold, and what little there is goes away quickly. The
engine is running well and making full power as far as I can
determine.


There's a guy at our marina who had a somewhat similar problem for a couple
of years. Turns out he had a very small air leak in the fuel supply line
for one engine. It would run fine after starting, (I assume because the
leak was overcome by fuel, but that is pure speculation), but was hard
starting.

Ain't boats fun?

Eisboch (grandkid #5 is a girl!)

Congrats! So what's the score now. I've got 4 grandsons, 1 granddaughter.

Detroit Diesel (DD671N) Questions
 

"JohnH" wrote in message
...

Eisboch (grandkid #5 is a girl!)

Congrats! So what's the score now. I've got 4 grandsons, 1 granddaughter.


Three girls, two boys. Need one more to even up the score.

Eisboch

Detroit Diesel (DD671N) Questions
 

On Tue, 24 Jan 2006 19:17:09 -0500, "Eisboch" wrote:

Ain't boats fun?

Eisboch (grandkid #5 is a girl!)

Congratulations! We are still at #0 but both sons are engaged so
that's a good start.

Yes, small air leak is a possibility under consideration. This issue
is fortunately not at a critical state yet but I like to stay on top
of things so I don't get a failure when I'm in the boondocks
somewhere.

Detroit Diesel (DD671N) Questions
 

"Wayne.B" wrote in message
...
On Tue, 24 Jan 2006 19:17:09 -0500, "Eisboch" wrote:

Ain't boats fun?

Eisboch (grandkid #5 is a girl!)

Congratulations! We are still at #0 but both sons are engaged so
that's a good start.

Yes, small air leak is a possibility under consideration. This issue
is fortunately not at a critical state yet but I like to stay on top
of things so I don't get a failure when I'm in the boondocks
somewhere.


Are your 671s turboed or normally 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.
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.

Eisboch

Detroit Diesel (DD671N) Questions
 

Wayne.B wrote:

On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi"
wrote:


I think you should identify symtoms,
if you want meaningful help.


It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt
within the last 1,000 hours or so by the previous owner.

My port side engine is taking longer to cold start than it used to,
sometimes needing 8 to 12 seconds of cranking. It used to start on
the first or second turn even when stone cold, and the starboard
engine still does. If it has been run within a day or two it still
starts very quickly. There is very little exhaust smoke at startup
even when cold, and what little there is goes away quickly. The
engine is running well and making full power as far as I can
determine.


Change the fuel filter, and if that doesn't help, look for a leak in
your supply lines.

--
"A prudent man foresees the difficulties ahead and prepares for them;
the simpleton goes blindly on and suffers the consequences." - Proverbs 22:3

Detroit Diesel (DD671N) Questions
 

Eisboch wrote:

"JohnH" wrote in message
...

Eisboch (grandkid #5 is a girl!)


Congrats! So what's the score now. I've got 4 grandsons, 1 granddaughter.



Three girls, two boys. Need one more to even up the score.

Eisboch


The M5 makes it an even score!

Dan

Detroit Diesel (DD671N) Questions
 

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.

Detroit Diesel (DD671N) Questions
 

"Dan Krueger" wrote in message
ink.net...
Eisboch wrote:

"JohnH" wrote in message
...

Eisboch (grandkid #5 is a girl!)


Congrats! So what's the score now. I've got 4 grandsons, 1 granddaughter.



Three girls, two boys. Need one more to even up the score.

Eisboch
The M5 makes it an even score!

Dan

Ah! The other "baby". Still working on the mandatory 1200 mile break in
procedure.
Pretty much got the hang of driving a manual without a clutch pedal though.
During break in you have to limit max RPM to 5500, so shifts are done around
4000-4500. After the break in period, max RPM is 8200 RPM with shifts around
6500 - 7000 which is getting into the engine's powerband. Can't wait to try
the "S6" mode. This car is going to get me in a lot of trouble.

Eisboch

Detroit Diesel (DD671N) Questions
 

On Tue, 24 Jan 2006 20:15:54 -0500, "Eisboch" wrote:


"Dan Krueger" wrote in message
link.net...
Eisboch wrote:

"JohnH" wrote in message
...

Eisboch (grandkid #5 is a girl!)


Congrats! So what's the score now. I've got 4 grandsons, 1 granddaughter.



Three girls, two boys. Need one more to even up the score.

Eisboch
The M5 makes it an even score!

Dan

Ah! The other "baby". Still working on the mandatory 1200 mile break in
procedure.
Pretty much got the hang of driving a manual without a clutch pedal though.
During break in you have to limit max RPM to 5500, so shifts are done around
4000-4500. After the break in period, max RPM is 8200 RPM with shifts around
6500 - 7000 which is getting into the engine's powerband. Can't wait to try
the "S6" mode. This car is going to get me in a lot of trouble.

Eisboch


Go visit Montana. I understand they're pretty lenient on speed out there. I
rode across the state and didn't get a ticket. That's proof.
--
John H

******Have a spectacular day!******

Detroit Diesel (DD671N) Questions
 

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?

Detroit Diesel (DD671N) Questions
 

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.

Detroit Diesel (DD671N) Questions
 

Wayne.B wrote:
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?

visual first, are they wet?
Check all nuts for tightness.
Clamps for tightness,
hoses for leaks or cracks.

It could be as simple as a banjo bolt washer that has compressed....

As I cannot see your installation, I can only give generalities.

I've seen it be as simple as a fuel filter gasket with a small pit in
it. The seal worked under pressure, but left a bit of air into the
system when everything cooled off and the pressure dropped.

Do you have any high points in the system where air could collect?

Do you have a mechanical fuel supply pump or an electrical one?
Hoses or hard pipe from the tank(s)?


If you have a leak, it is currently a small one from your symptoms. If
it was major, you'd have real trouble starting at all.

--
"A prudent man foresees the difficulties ahead and prepares for them;
the simpleton goes blindly on and suffers the consequences." - Proverbs 22:3

Detroit Diesel (DD671N) Questions
 

"Wayne.B" wrote in message
...
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

Detroit Diesel (DD671N) Questions
 

On Tue, 24 Jan 2006 19:35:50 -0600, dazed and confuzzed
wrote:

Do you have any high points in the system where air could collect?


Don't think so but I'll take another look.

Do you have a mechanical fuel supply pump or an electrical one?

Mechanical

Hoses or hard pipe from the tank(s)?

Hoses

Detroit Diesel (DD671N) Questions
 

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.

Detroit Diesel (DD671N) Questions
 

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.

Detroit Diesel (DD671N) Questions
 

"JohnH" wrote in message
...
On Tue, 24 Jan 2006 20:15:54 -0500, "Eisboch" wrote:


"Dan Krueger" wrote in message
hlink.net...
Eisboch wrote:

"JohnH" wrote in message
...

Eisboch (grandkid #5 is a girl!)


Congrats! So what's the score now. I've got 4 grandsons, 1
granddaughter.



Three girls, two boys. Need one more to even up the score.

Eisboch
The M5 makes it an even score!

Dan

Ah! The other "baby". Still working on the mandatory 1200 mile break in
procedure.
Pretty much got the hang of driving a manual without a clutch pedal
though.
During break in you have to limit max RPM to 5500, so shifts are done
around
4000-4500. After the break in period, max RPM is 8200 RPM with shifts
around
6500 - 7000 which is getting into the engine's powerband. Can't wait to
try
the "S6" mode. This car is going to get me in a lot of trouble.

Eisboch


Go visit Montana. I understand they're pretty lenient on speed out there.
I
rode across the state and didn't get a ticket. That's proof.
--
John H

******Have a spectacular day!******

When the nationwide 55 speed limit was in affect. Wyoming gave a $5 wasting
natural resources ticket. Probably the same in Montana. Unless you are in
one of the speed zone areas.

Detroit Diesel (DD671N) Questions
 

Appears the 671 has 2 valves.
http://www.dieseldhp.com/cgi-bin/get....cgi?refno=140


"Calif Bill" wrote in message
nk.net...

"JohnH" wrote in message
...
On Tue, 24 Jan 2006 20:15:54 -0500, "Eisboch" wrote:


"Dan Krueger" wrote in message
thlink.net...
Eisboch wrote:

"JohnH" wrote in message
...

Eisboch (grandkid #5 is a girl!)


Congrats! So what's the score now. I've got 4 grandsons, 1
granddaughter.



Three girls, two boys. Need one more to even up the score.

Eisboch
The M5 makes it an even score!

Dan

Ah! The other "baby". Still working on the mandatory 1200 mile break
in
procedure.
Pretty much got the hang of driving a manual without a clutch pedal
though.
During break in you have to limit max RPM to 5500, so shifts are done
around
4000-4500. After the break in period, max RPM is 8200 RPM with shifts
around
6500 - 7000 which is getting into the engine's powerband. Can't wait to
try
the "S6" mode. This car is going to get me in a lot of trouble.

Eisboch


Go visit Montana. I understand they're pretty lenient on speed out there.
I
rode across the state and didn't get a ticket. That's proof.
--
John H

******Have a spectacular day!******

When the nationwide 55 speed limit was in affect. Wyoming gave a $5
wasting natural resources ticket. Probably the same in Montana. Unless
you are in one of the speed zone areas.

Detroit Diesel (DD671N) Questions
 

And the 4 valve is a Turbo intercooler head.
http://boatdiesel.com/Forums/Index.c...108&CFIDC=NRU2

"Calif Bill" wrote in message
nk.net...

"JohnH" wrote in message
...
On Tue, 24 Jan 2006 20:15:54 -0500, "Eisboch" wrote:


"Dan Krueger" wrote in message
thlink.net...
Eisboch wrote:

"JohnH" wrote in message
...

Eisboch (grandkid #5 is a girl!)


Congrats! So what's the score now. I've got 4 grandsons, 1
granddaughter.



Three girls, two boys. Need one more to even up the score.

Eisboch
The M5 makes it an even score!

Dan

Ah! The other "baby". Still working on the mandatory 1200 mile break
in
procedure.
Pretty much got the hang of driving a manual without a clutch pedal
though.
During break in you have to limit max RPM to 5500, so shifts are done
around
4000-4500. After the break in period, max RPM is 8200 RPM with shifts
around
6500 - 7000 which is getting into the engine's powerband. Can't wait to
try
the "S6" mode. This car is going to get me in a lot of trouble.

Eisboch


Go visit Montana. I understand they're pretty lenient on speed out there.
I
rode across the state and didn't get a ticket. That's proof.
--
John H

******Have a spectacular day!******

When the nationwide 55 speed limit was in affect. Wyoming gave a $5
wasting natural resources ticket. Probably the same in Montana. Unless
you are in one of the speed zone areas.

Detroit Diesel (DD671N) Questions
 

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

Detroit Diesel (DD671N) Questions
 

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.

Detroit Diesel (DD671N) Questions
 

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.

Detroit Diesel (DD671N) Questions
 

On Wed, 25 Jan 2006 14:49:55 +0000, Butch Davis wrote:

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

First good advise that has been given. The tools are availible here.
You will only need the one tool for the type injector that is in your engine.

http://buy1.snapon.com/catalog/tools...e=snapon-store

I own a set of four that I've had for about thirty-five years.
They won't go bad, and you will only need one.

alt.binaries.pictures.sports.ocean, has some info.

Detroit Diesel (DD671N) Questions
 

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.

Detroit Diesel (DD671N) Questions
 

In article ,
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. 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;

Well it is obvious that Larry has never wrenched on a Scream'in
Jimmy of any kind, or he would have known, that they ALL have
Exhaust Valves, in the HEAD, under the VALVE COVER.... where the
Injectors ARE......


Me

Detroit Diesel (DD671N) Questions
 

Wayne,

1st: on a 671... no smoke usually means compression is fine. If
compression was bad, you would get smoke on startup until they warm. if
it warms and they still smoke badly... you need a rebuild fast... If it
runs after fuel is shut off or it runs away then you needed a rebuild
last year.

2nd: Do you have Racors? Is the fuel level in the tank ABOVE or BELOW
the injectors? If the answer is YES and BELOW then go buy a Racor
rebuild kit or at least buy the washer that sits over the metal ball.
That washer will disfigure over time causing the ball to not seat and
the fuel will drain back into the tank. Also make sure all other seals,
especially the top seals are in good shape (A rebuild kit comes with all
new seals)


3rd: Is the engine turning over the normal speed? If not, batteries may
be low. A slow turnover will cause an engine to slow start.

4th: DO your exhaust ports have the heat sheilds over them? If not,
you can use a temp gun to find a bad cylinder. If not, you can play with
the fuel rack with the cover off to find a bad cylinder. (Not
recommended unless you know what you are doing or have 6 fingers on your
right hand) BUT AGAIN... no smoke means you probably have 6 good
cylinders.

5th- Spend 90% of your time playing with the inbound fuel system. A few
hints: While the engine is running.. everything PAST the lift pump
(The first pump after the racor) is under PRESSURE. Check this area
first for leaks while the engine is running-higher speed the better.
Everything BEFOre the lift pump is under SUCTION. This is harder to
find because there will be no visible fuel most of the time. (See #2)
You can put some semi-viscous liquid around the seals and see if it is
sucked in but that can be difficult to see. (Spit, clean oil, etc)

Don's waste your money on a compression check ($500 +++) until you
have tried most everything else

Have fun... I am in a similar situation with one of our boats but we
have smoke and 1 bad cylinder.... kind of a smoking gun...

Ed
ed at Estrobel dot com




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.

Detroit Diesel (DD671N) Questions
 

Eisboch wrote:
"Wayne.B" wrote in message
...

On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi"
wrote:


I think you should identify symtoms,
if you want meaningful help.

It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt
within the last 1,000 hours or so by the previous owner.

My port side engine is taking longer to cold start than it used to,
sometimes needing 8 to 12 seconds of cranking. It used to start on
the first or second turn even when stone cold, and the starboard
engine still does. If it has been run within a day or two it still
starts very quickly. There is very little exhaust smoke at startup
even when cold, and what little there is goes away quickly. The
engine is running well and making full power as far as I can
determine.



There's a guy at our marina who had a somewhat similar problem for a couple
of years. Turns out he had a very small air leak in the fuel supply line
for one engine. It would run fine after starting, (I assume because the
leak was overcome by fuel, but that is pure speculation), but was hard
starting.

Ain't boats fun?

Eisboch (grandkid #5 is a girl!)



Hi again, you say it's making full revs??? a fixed pitch prop is an
excellent dynomometer so if it were seriously down on compression I
think you'd see it in the top end max revs performance.

I think before you go too much further you might check the fuel supply
especially as you say it starts easier after a day, but by then it's
well cold so any mechanical defect in the compression etc would still be
there.

Seems granddad Eisboch is on the trail here (he's having a good
day???:-)), fuel filters are a good source of air leaks also. It might
be slowly allowing the fuel to go back down the lines & air in.

These engines as with many Cummins, don't have an injector pump in the
commonly known sense, they have a moderately pressurised fuel rail not
unlike the one in your petrol car. Along this rail (they call it a fuel
manifold in the manual) the unit injectors are sited. There is a
restriction in the fuel rail outlet to maintain feed pressure to the
unit injectors, if the fuel rail isn't properly pressurised by the gear
pump supply it won't start ......... easily. The injectors are driven by
the camshaft & rocker arms the same as the valves are & do the final
pressure increase & injection all in the one movement (pump injector
combination).

You can imagine if your fuel system, the gear fuel rail pressure pump as
mentioned (which is also the lift pump usually), the fuel rails & the
unit injectors themselves, get any air in there it will need a few turns
to pump it through & clear it. Once started they can live with a tiny
airleak becasue it just goes straight through the system & out the
return line.


K

Detroit Diesel (DD671N) Questions
 

"K. Smith" wrote in message
...
Eisboch wrote:
"Wayne.B" wrote in message
...

On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi"
wrote:


I think you should identify symtoms,
if you want meaningful help.

It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt
within the last 1,000 hours or so by the previous owner.

My port side engine is taking longer to cold start than it used to,
sometimes needing 8 to 12 seconds of cranking. It used to start on
the first or second turn even when stone cold, and the starboard
engine still does. If it has been run within a day or two it still
starts very quickly. There is very little exhaust smoke at startup
even when cold, and what little there is goes away quickly. The
engine is running well and making full power as far as I can
determine.



There's a guy at our marina who had a somewhat similar problem for a
couple of years. Turns out he had a very small air leak in the fuel
supply line for one engine. It would run fine after starting, (I assume
because the leak was overcome by fuel, but that is pure speculation), but
was hard starting.

Ain't boats fun?

Eisboch (grandkid #5 is a girl!)



Hi again, you say it's making full revs??? a fixed pitch prop is an
excellent dynomometer so if it were seriously down on compression I think
you'd see it in the top end max revs performance.

I think before you go too much further you might check the fuel supply
especially as you say it starts easier after a day, but by then it's well
cold so any mechanical defect in the compression etc would still be there.

Seems granddad Eisboch is on the trail here (he's having a good
day???:-)), fuel filters are a good source of air leaks also. It might be
slowly allowing the fuel to go back down the lines & air in.

These engines as with many Cummins, don't have an injector pump in the
commonly known sense, they have a moderately pressurised fuel rail not
unlike the one in your petrol car. Along this rail (they call it a fuel
manifold in the manual) the unit injectors are sited. There is a
restriction in the fuel rail outlet to maintain feed pressure to the unit
injectors, if the fuel rail isn't properly pressurised by the gear pump
supply it won't start ......... easily. The injectors are driven by the
camshaft & rocker arms the same as the valves are & do the final pressure
increase & injection all in the one movement (pump injector combination).

You can imagine if your fuel system, the gear fuel rail pressure pump as
mentioned (which is also the lift pump usually), the fuel rails & the unit
injectors themselves, get any air in there it will need a few turns to
pump it through & clear it. Once started they can live with a tiny
airleak becasue it just goes straight through the system & out the return
line.


K

I think some people put pressure guages before and after the fuel filter.
You would know what the pressure is when starting and if the fuel filter is
getting clogged.

Detroit Diesel (DD671N) Questions
 

Wayne,
This is simple. You have fuel feed leakdown on that engine. On the detroits,
you have a gearpump that draws fuel from the tank and pushes the fuel
through a strainer and then a filter. From the filter it enters the Cylinder
head where it passes through a cast feed log. Unused fuel is turned around
and again passed through the return log in the head. From there it is
returns heated to the tank. Fuel pressure at the out side of the pump should
be about 45 lbs. Your problem is that the feed line to the inlet of the pump
is draining back to the tank. Probably a very small leak in that line.
Steve


"Wayne.B" wrote in message
...
On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi"
wrote:

I think you should identify symtoms,
if you want meaningful help.

It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt
within the last 1,000 hours or so by the previous owner.

My port side engine is taking longer to cold start than it used to,
sometimes needing 8 to 12 seconds of cranking. It used to start on
the first or second turn even when stone cold, and the starboard
engine still does. If it has been run within a day or two it still
starts very quickly. There is very little exhaust smoke at startup
even when cold, and what little there is goes away quickly. The
engine is running well and making full power as far as I can
determine.

Detroit Diesel (DD671N) Questions
 

"Steve Lusardi" wrote in message
...

Wayne,
This is simple. You have fuel feed leakdown on that engine. On the
detroits, you have a gearpump that draws fuel from the tank and pushes the
fuel through a strainer and then a filter. From the filter it enters the
Cylinder head where it passes through a cast feed log. Unused fuel is
turned around and again passed through the return log in the head. From
there it is returns heated to the tank. Fuel pressure at the out side of
the pump should be about 45 lbs. Your problem is that the feed line to the
inlet of the pump is draining back to the tank. Probably a very small leak
in that line.
Steve



Wayne, I might add that the guy with the similar problem that I mentioned
before also had DD671s, FWIW

Eisboch

Detroit Diesel (DD671N) Questions
 

On Thu, 26 Jan 2006 10:00:09 +0100, "Steve Lusardi"
wrote:

This is simple. You have fuel feed leakdown on that engine. On the detroits,
you have a gearpump that draws fuel from the tank and pushes the fuel
through a strainer and then a filter. From the filter it enters the Cylinder
head where it passes through a cast feed log. Unused fuel is turned around
and again passed through the return log in the head. From there it is
returns heated to the tank. Fuel pressure at the out side of the pump should
be about 45 lbs. Your problem is that the feed line to the inlet of the pump
is draining back to the tank. Probably a very small leak in that line.
Steve

Thanks, good description. I think I'll start by replacing the engine
mounted fuel filters and gaskets since there seems to be a consensus
that the problem is somewhere in that area. The fuel tanks are 75%
full right now which puts the fuel level above the engines, so that
should rule out an issue with the Racors if I understand this
correctly.

Detroit Diesel (DD671N) Questions
 

On Thu, 26 Jan 2006 04:50:08 -0500, "Eisboch" wrote:

Wayne, I might add that the guy with the similar problem that I mentioned
before also had DD671s, FWIW

Thanks, do you happen to know how he located the leak?

Detroit Diesel (DD671N) Questions
 

"Wayne.B" wrote in message
...
On Thu, 26 Jan 2006 04:50:08 -0500, "Eisboch" wrote:

Wayne, I might add that the guy with the similar problem that I mentioned
before also had DD671s, FWIW

Thanks, do you happen to know how he located the leak?


I don't. Next time I go down to check the boat, I'll ask.

Eisboch