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?

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.

"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!)

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.

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

"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.

On Thu, 26 Jan 2006 06:38:42 GMT, "Calif Bill"
wrote:

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.

I have vacuum guages on the suction side of my Racors to provide a
warning if they are starting to load up.

Everything looks normal there.

Wayne, when the engine is in the "hard to start condition", and then it
finally starts, does it do so on all cylinders, or does it go thru a
period where only 1, 2, 3, etc cylinders are firing for a while before
all 6 finally kick in? This could indicate a very slow leak between the
injection pump and the injectors.

bob


Wayne.B wrote:
On Thu, 26 Jan 2006 06:38:42 GMT, "Calif Bill"
wrote:


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.


I have vacuum guages on the suction side of my Racors to provide a
warning if they are starting to load up.

Everything looks normal there.

I agree with the fuel system diagnosis. Have you changed the fuel filters,
checked the fuel water separator etc.
Fredo

"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

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