GM 4-71 - Crankcase breather - smokey!

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Mar 27, 2011
2
CAL 30 Bay Area
At idle and warmed up, there is white smoke pouring out of the breather, additional white smoke and traces of oil are coming out of the wet exhaust - Rings?

Thanks.
 
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Nov 6, 2006
9,884
Hunter 34 Mandeville Louisiana
Could be .. or could be water getting into the crankcase. Water pump seal leaking into crankcase?? I don't know the configuration of that engine's pump If the oil is nice and clean, (ok, black and not whiteish) then rings or head gasket or cracked head. That engine is a bit strange for small marine use since it is a two stroke that is scavenged by a blower. Is that engine on your Cal 30??
 
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Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
The cranks case on a 2-cycle does not have a breather. I don't know if kloudie1 is correct in his assertion that it is a 2-cycle or you are correct in your assertion that it is infact the crankcase breather.
For the record a 2 cycle engine used the crankcase as part of the induction plumbing. to put a breather here would only result in it adding air from the engine compartment (induction is under vacume) not it blowing fumes out.
Can we confirm that the GM 4-71 is a 2 cycle engine and not a 4 cycle?
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
Correction, a diesel 2-cycle would not have the induction under vacume. You would still not plumb a breather to it however as that serve no purpose. It would just let more air in. also since there is smoke coming from the "breather" there must be either oil or fuel in it. that only happens after the compression stroke and in the exhaust.
Do we have a picture of this beast. the only thing I found on the internet was a 1941 2-cycle diesel that was a pretty big and cumbersum looking unit. Pretty sure that is not what you have.
 

bria46

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Jan 15, 2011
286
Oday 272 Waukegan, IL, Sarasota, FL
I just attended a diesel seminar. Presented by Westerbeke. The service rep. stated that (4 cycle diesels) White smoke = Not enough diesel fuel at the injectors. Black smoke = Too much fuel at the injectors.
 
Mar 27, 2011
2
CAL 30 Bay Area
This is a boat I'm looking to buy. Current owner connected a shopvac hose to vent the smoke outside the engine compartment... Pictures below - The GM is a two cycle 4-71A. Thanks.
 

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Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
Does the "smoke" disipate (like steam) or hang around the boat?
 
Jun 26, 2007
106
Freedom F39 Lyttelton New Zealand
The local Detroit Diesel dealer here often sells a Walker Air Seperator (if I remember the name correctly) for the GM 2 stroke engines. Apparently these engines are fairly heavy breathers and will put an oil film on everything in the engine compartment if the breather just discharges to atmosphere. The seperator takes breather air to the inlet manifold while seperating the oil and draining it back to the sump. Excessive discharge from the breather might indicate high crankcase pressure which would in turn indicate worn piston rings. This should also manifest in hard starting. So it could be worn rings or it could be just normal for a 4-71, without an air seperator.

Regards,
 
Nov 22, 2008
3,562
Endeavour 32 Portland, Maine
For the record a 2 cycle engine used the crankcase as part of the induction plumbing.
For the record, this is wrong. It's true for 2 cycle gas engines but the GM two strokes have an air path entirely separate from the crank case. That's what the Roots blower on the side that gives them that distinctive whine does. They also have crankcase breathers that were so famous for filling engine rooms with a fine oil mist that they spawned a whole aftermarket industry.

This engine sounds as if it could be very, very sick. This is a question for a professional not a forum.
 
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