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Old 11-10-2017, 02:10 AM   #1
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Cummins 6BTA 315 Power loss

Hi

Have recently lost power in one of my Cummins 6bta 315's.
I can now get no more than 1850 rpm and now blows black smoke, we should be able to get 2800.
Engine runs as it should up to 1850rpm, no smoke and runs smooth as silk.
Had the Cummins tech down for a look and he says engines are not the issue.
The boat is jet driven and he seems to think it must be the jet binding up.
Have checked jets and they are all clear and can turn shafts by hand.
Someone else has said it may be an Intercooler obstruction(air side).
Turbo and airfilter all good.

Any ideas ?

Thanks
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Old 11-10-2017, 08:35 AM   #2
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Aftercooler may need cleaning or something worse. How much crankcase blowby are you seeing?
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Old 11-10-2017, 08:50 AM   #3
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Turbo spin free with fingertips? It might spin free engine off, but can bind under running conditions if bearing play is excessive. Go for a run with airfilter off and watch for spin

Put a boost gauge on the tap on intake manifold just fwd of air intake pipe. At 1850 full load you should have at least 5-7psi boost (guessing).
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Old 11-10-2017, 10:04 AM   #4
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Yes it could be engine, but assuming Cummins tech is correct -- Jet drives are a pump. Bearings, impeller, clearance and shaft issues can and do arise. When was last time pump was pulled, inspected and serviced? Any chance a rope is lodged in the pump?

Berkeley, American or ?? pump?
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Old 11-10-2017, 10:12 AM   #5
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"I can now get no more than 1850 rpm and now blows black smoke, we should be able to get 2800.
Engine runs as it should up to 1850rpm, no smoke and runs smooth as silk."

Most likely you are not getting boost to the engine.
Ski has a great response - check boost underway under load.
Also check any flexible hose that transfers the boosted air intake charge to the engine - there can be a thin rip or tear that leaks the boost when under pressure. Check the hose carefully as well as all of the clamps.
Please let us know what you find and good luck.
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Old 11-10-2017, 10:13 AM   #6
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could be something simple like a blown air hose of busted clamp leaking boost.
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Old 11-10-2017, 03:34 PM   #7
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Do the simple things first change fuel and air filters ck the air vent on the fuel tank.
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Old 11-10-2017, 04:34 PM   #8
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Do the simple things first change fuel and air filters ck the air vent on the fuel tank.
Black smoke as the OP reported usually means it is getting plenty (or too much for the available air) of fuel. Check the turbo as Ski suggests.

David
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Old 11-11-2017, 07:46 AM   #9
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Thanks for all the info.
Will check all hoses etc tomorrow and let you all know how it goes.
Will be slipping the boat early next week for her yearly maintenance and will check jet drives.
Regards
Bluetide
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Old 11-11-2017, 08:30 AM   #10
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Was your avatar pic taken in Erie,Pa?
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Old 11-11-2017, 01:16 PM   #11
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Sailor of Fortune it was taken in Melbourne Australia.
That is my Willard Marine UB40 I restored a few years ago.
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Old 11-11-2017, 11:48 PM   #12
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Nice ride
Did you really put twin 315’s in that boat?
My Willard 50 MUB does quite well on its single Cummins 6BT at 180 hp.
I would like to see your performance/fuel burn numbers!
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Old 11-12-2017, 06:05 AM   #13
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Nice ride
Did you really put twin 315ís in that boat?
My Willard 50 MUB does quite well on its single Cummins 6BT at 180 hp.
I would like to see your performance/fuel burn numbers!
No she has the unbreakable Detroit 671n.
My crew transfer vessel has the twin Cummins.
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Old 11-12-2017, 11:43 AM   #14
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My bet is the turbo. ANd as ski suggested, it sounds complicated or beyond the realm of some people(like me), but screwing in a boost gauge on the intake manifold is EXTREMELY easy as the tappet is already there. Good luck!!!
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Old 11-14-2017, 08:00 AM   #15
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Hi

We found our issue.

The intercooler was blocked with oil.

Just got to make sure we service them every 200 hours.

Thanks everyone for your input.

Cheers
Bluetide
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Old 11-14-2017, 08:08 AM   #16
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Quote:
Originally Posted by Bluetide View Post
Hi

We found our issue.

The intercooler was blocked with oil.

Just got to make sure we service them every 200 hours.

Thanks everyone for your input.

Cheers
Bluetide
Post +2 nailed it. Seems the Cummins guy didn't. Would re-routing breather to a puke bottle per Tony Athens be of benefit? Amazing how much oil mist they pick up.
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Old 11-14-2017, 08:23 AM   #17
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Sunchaser every little bit would help.
I seem to learn the hard way.
Ran to long on the air filters creating a vacuum allowing oil to enter the inter cooler .
We also didn't utilise our engine room fans to supply clean air.
Lessons learnt for sure.
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Old 11-14-2017, 08:23 AM   #18
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Quote:
Originally Posted by Bluetide View Post
Hi

We found our issue.

The intercooler was blocked with oil.

Just got to make sure we service them every 200 hours.

Thanks everyone for your input.

Cheers
Bluetide
This service should not only be based on hours but also on age/time. They also corrode and corrosion is a function of time. 200 hours also seems a bit aggressive. That would be less than a year for me and for commercial guys that would be many times a year. I do mine every 3 years and they are fine. And that equates to about 700 hours. Nothing wrong with doing them more often but it just seems like a bit much.
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Old 11-14-2017, 11:00 AM   #19
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I have the same engines and got rid of the Walker system and replaced it with the Racor system of filtering the blowby. racor CCV4500 blowby filter and matching Air filter system. It doubles my aftercooler service intervals and the engines run very clean


https://www.parker.com/literature/Ra...CCV_Series.pdf
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Old 11-14-2017, 11:12 AM   #20
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Oily blowby rarely clogs the charge air cooler. The slime usually blows through with little effect. To clog there must be oil and some sort of particulate.

Certainly clean it, but not sure it will fix the issue. Will know on the test run.
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