Detroit Diesel (DD671N) Questions

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?

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.

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.

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.

Dan

Eisboch

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

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.

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

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

Mechanical

>Hoses or hard pipe from the tank(s)?

Hoses

Gaz

"Wayne.B" <waynebatrecdotboats@hotmail.com> wrote in message

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.

Ain't boats fun?

Eisboch (grandkid #5 is a girl!)

Eisboch

er......

never mind....

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