Cummins Marine Diesel Engine, Problems

We are in the throes of re-powering Morgan’s Cloud, and as far as we are concerned, this unpleasant and expensive task has come about 4000 engine hours too early.

A couple of years ago we started to notice that we were getting much more soot on the transom from the exhaust than we liked. Then last year we started to see un-burned fuel on the water aft of the boat and coating the dinghy. Clearly all was not well even though the engine continued to start easily and run reliably, as it always had.

We pulled the injectors and had them rebuilt. We pulled the injection pump and had it calibrated and rebuilt. Still the problem got worse. Then we started to lose top-end RPM, a sure symptom of loss of power.

Finally we did a blow-by test in which we measured the amount of gas pressure in the crank case. Oh-oh, off the scale. Either the valves were not seating properly or exhaust gas was blowing by the rings. As the head came off, we hoped for the former—a  comparatively easy fix with a valve job.

But it was not to be. David, ace machinist at Billings Diesel and Marine, checked the cylinders for wear with a bore gauge and discovered that they were out of round. And that’s when it got weird: The cross hatch pattern that was etched onto the cylinder walls during manufacturing was still in almost perfect condition, indicating that there had been no appreciable wear. Further, we had never overheated the engine and the oil samples that we had analysed at every oil change had never shown excessive fragments.

A vague bell went off in my memory: When the engine was new we had a problem with fumes in the engine room. I measured blow-by at that time and had even written the result in an old log, which, miracle of miracles, we were able to find. The reading: 8 inches of water. At the time, I had called Cummins North East (CNE), the dealer that sold me the engine, to ask about this reading and was told that it was not a problem and that the maximum for a new engine was 12 inches. But the Cummins document we found last year seems to indicate (it is not as clear as one would like) that 3 inches is the maximum for this engine!

By the way, CNE  then sold me a crank case re-breather system to solve the problem of exhaust in the engine room, which never did work well until heavily modified by Billings.

All of the above leads to one inescapable, at least to us, conclusion: The engine was bored out of round when new—a lemon, pure and simple. Even if that was not the case, this kind of problem at 6000 hours on a diesel engine that has always been meticulously maintained is just not good enough.

This comes on top of another manufacturing mistake by Cummins (stripped bolts on the oil pan) that we experienced with the same engine.

As we always do with this kind of post, we offered Cummins and CNE the opportunity to comment. They wrote us a brush off email.

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