Gordon:
You restated your problem, ok, so now listen to my restatement of diagnosis you need to make to find the cause:
As Ski noted earlier, most boat systems direct crankcase blowby back to the air intake. Usually it is not very oily, but three things can make it oily: bad rings, an overfilled crankcase and an AirSep system.
You can easily check for bad rings by putting your hand in front of the blowby tube while there is some load on the engine. You will feel heavy exhaust pulses. Or remove the filler cap and feel for pulses.
An overfilled crankcase can let the crankshaft whip the oil up and out the blowby vent. This is probably the most likely cause. Lower the oil level by a quart and see what happens.
Finally an AirSep system can overpressure the crankcase and force oil out with the blowby and then into the intake. They work fine on DD 2 strokes but especially on the Cummins B, they do not. That is why Seaboard Marine (Tony Athens' company) developed their Envirovent system for the Cummins B and C.
AirSeps were factory installed on some Bs and yours may have them. Read the following. It is detailed and tedious but it describes exactly what may be happening to your engines: EnviroVent CCV Kit 4BT & 6BT Series - Seaboard Marine
Check for these three problems before rebuilding your turbos. I'll bet it is one of them.
David
Gordon:
I am no expert on turbo failures, but if it is a lubrication related failure, the bearings will get loose and the turbo blades will start to rub on the housing and the turbo will stop turning. I think that you will get plenty of warning due to not being able to hit the rated rpms of the e
David
If blowby vents outside the boat, and if by chance there is a low spot in the hose, oil will a accumulate there and form a liquid trap. That will pressurize the crankcase and force oil out the turbo shaft seals.
Yep, if blowby is vented into turbo as most are, some oil can ooze around compressor scroll and is a non-issue.
On a B-motor, the envirovent system is a big improvement over the factory blowby vent.
So I found the blow by today. On this boat, the blow by Vince to the outside via a 10 foot long 1 inch hose. So, the oil is deafly not coming from the blow by. A mechanic friend of mine looked at it and said clearly the oil is coming from a leaking oil seal on the turbos.
His take was that as long as there is oil the bearings are in no danger and will probably get some more use out of the turbos. I am still thinking about changing them,however, or I should say getting them rebuilt while I have the exhaust system apart.
With the idea that a lot of methods are interesting, may even be
inspirational, though not directly applicable, here is a picture.
The engine is a Cat 3406. The vent tube is 1 1/2 or 2 inch, it
follows the exhaust pipe (dry) to exit through the stack on the cabin top.
Ted
Don't bite the hand...I have to say I am so far disappointed in the response to my query from Boat Diesel. Ski seems to have the best idea what is going on. Tony Athens can't seem to follow the thread from one day to the next, or, I am being impatient.
I am being impatient.
Gordon
I take back all said. I thought this was part of his business, and did not understand that he was an unpaid volunteer. I do respect that.
Gordon