If the engines are turbo intercooled it might be that the intercooler is
partially blocked
the induction air is too hot and has of low density
giving incomplete combustion
Good Luck!!
Steve


"Mike" wrote in message
om...
I have 2 Cummins 6bt5.7M (4k hours) that are beginning to smoke and
leave a film at the exhaust (sea water output). The port engine is the
worst, but both engines have the same problem. In trying to identify
the problem I've preformed the following test.
1) no (or very little) oil usage.
2) Both Engines run at 180 deg.
3) Turbo output 2600rpm (port)16psi (starb) 18psi Cummins manual
calls for 20-25psi. No intake obstructions. No leaks detected any
place from output of turbo up to and including the intake manifold. No
detectable leaks in exhaust. No restrictions in oil return line.
4) Turbo (Holset H1C) compressor impeller can be pushed to contact the
housing. (I would guess .100" movement) Holset calls for .012" -
.018" radial movement
5) Turbo axial movement .010 both sides. Holset calls for .025.
6) Blowby (taken with the Cummins recommend setup using calibrated
0-100"h20 gauge with dipstick hole blocked). at 1000rpm approx. 2"
(both engines) but at 2600 rpm 0".
(I've ordered a diesel compression tester hope to have it next weekend
while I'm testing the compression, I'll get the injectors tested)

These are the steps that I've taken so far. The most glaring result to
me is the blowby. There is none detected at rated speed. I've talked
to the Cummins dealer, he says that it can't be and recommend using a
manometer instead of the gauge.
The turbo's are bad according to the holset manual so I pulled them
and brought them to be rebuilt (holset authorized). The mechanic
looked at them when I dropped them off and While he didn't come out
and say so, I got the impression that he thought they were ok. He will
be taking them apart this week.

OK, now for my diagnosis;
The smoke and sheen that I see are unburned diesel. The cause is low
turbo pressure not getting enough air into the cylinders. The low
turbo pressure is
Caused by bad oil seals in the turbos allowing crankcase pressure to
be reduced by the vacuum of the turbo compressor. The question of why
would both engines have the same problem comes up. My theory is; when
changing fuel filters, I use starting fluid to get the fuel to start.
The ether (or other chemicals in the starting fluid) has caused the
seal to deteriorate.

Anyone have any feedback? The engines are honey's. They have never
failed in the 10 years we've owned the boat ( 3000hrs). The smoke is
not a killer yet, but I would like to solve the problem before it gets
worse.

Thanking anyone in advance for advice, criticism or observations.

Mike