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I have an early 6BT (CPL 742) in my 1987 Albin 36 trawler. It’s been going through a refit for the past two years. My wife and I just completed a 1,100-mile shakedown cruise to FL and back to our home in NC. It’s always been a little smokey so I researched some possible causes. The smoking is both on a cold start and after a day of cruising.
I replaced all the old (probably original) 9mm injectors with new Cummins injectors (CPN 3802333) purchased directly from Cummins. My engine has the old CAV rotary injection pump. The engine fires right up every time.
This past week my local diesel class instructor and I ran compression tests on all my cylinders. The compression average was 409 psi (+/- <10%). I have adjusted the valves per my engine manual (0.020 exhaust and 0.010 intake). I verified my EnvironVent system was clear of any obstructions. My air filter is in good shape (only about 200 hours on it). My fuel burn running at 1,700 rpm for our trip averaged 3.4 gph which I felt was normal. I do not seem to be consuming excessive oil. I also checked the coolant daily and it is not consuming any. The temperature sits right at 180 degrees once underway.
The hours on the engine are a mystery since neither of the hour meters worked when we purchased the boat. My best guess is around 5,000 hours. What is normal exhaust smoke for a 38-year-old mechanical diesel engine? Any insight will be appreciated.
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Have you considered that you may be overpropped? <br />Fuel burn seems high for a low hp B motor, and black smoke is another indicator.
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Vessel Name: overslept
Engines: Twin 4BT CPL741
Location: Massapequa Park, New York Long Island
Country: USA
Since you have recently completed an 1100 mile journey with your 6BT I would have to say that what ever is happening it cant be all that bad…(I know famous last words…)
Seriously, being that you have a trawler I kind of think that maybe you are not cruising at a high RPM.
Do you normally do a lot of idling or low RPM cruising?
I ask this because these engines like to be operated at normal operating temperature. Low idling will allow combustion temperatures to run lower than Cummins likes.
The side effect of low combustion temperatures is smokey running. Excess carbon builds up on the piston tops and the fuel does not completely burn and gets sent out the exhaust.
You can try and make sure run the boat at wide open throttle (high idle) for a few minutes every time you go out for a cruise. See if that helps.
Running the engine at WOT (for a few minutes) is not anything to be afraid of. It will also let you know if you are propped properly (you need to get 2700…I think 2600 is rated for the CPL 742 but I am not sure tho) You want 100 OVER rated RPM at wide open throttle
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