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Old 02-13-2016, 01:52 PM   #1
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Cummins mystery dust

So we overhauled a Cummins 6TBA 5.9-M3. The engine runs perfectly on several 2 hour trips, but I'm noticing black small bits on the engine room on the aft engine room floor as though a belt were coming apart. The only exposed belt is in the front of the engine and this is back by the turbo and after cooler and transmission. Any thoughts? Thanks, Tim
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Old 02-13-2016, 02:01 PM   #2
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look at the vent on top of the transmission to see if it comes from the coupling plate.
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Old 02-13-2016, 02:36 PM   #3
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Sounds like a possibly. Does it have bad implications for the transmission.? Is there a remedy?
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Old 02-13-2016, 08:00 PM   #4
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The coupling plate has rubber bumper-things in there that wear a bit. Did you replace them when you did the overhaul or was it an inframe? If they are old they could be perishing/disintegrating, if they are new they could just be getting seated.

Make sure you only shift gears at idle. I would not worry about the black stuff until the coupler starts rattling.
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Old 02-13-2016, 08:04 PM   #5
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Carbon from exhaust ?
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Old 02-13-2016, 08:14 PM   #6
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Quote:
Originally Posted by ghost0070 View Post
Sounds like a possibly. Does it have bad implications for the transmission.? Is there a remedy?
A coupler joins engine with trans, so no, trans is fine if it is the coupler.
My coupler has no rubber, just splined center, springs arranged in a circle, flat plate that bolts to engine. Looks like a clutch disc without the friction material.

What mine looks like from when I rebuilt the engine


I cleaned it, primed it then re oiled with gear oil. In perfect shape from 1970.
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Old 02-14-2016, 09:36 AM   #7
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Coupler

There are different styles of couplers. Mine was heavy duty and did have springs and rubber so don't Ryle that out.
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Old 02-14-2016, 10:49 AM   #8
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I have the same engine and do find a little fine black dust from the belt fwd. Inside the belt guard and black specks around the transmission to engine coupling vent slits. I don't think either is a problem but do not know how much wear is acceptable at the coupling. Belts are easy to check and change the coupling not so. I have not noticed any rattling or slop there. 2003 year and about 2800 hrs.
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Old 02-14-2016, 11:06 AM   #9
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First find where the bits are coming from. From your description the trans is suspect but it could be the trans or something else. Look at the bell housing vents. There are other rubber items at the rear such as hoses, mounts etc that could be rubbing on something.


First rule of problem solving is respect all recent work.
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Old 02-14-2016, 12:34 PM   #10
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Ghost,

My initial response would be that a small amount of black "dust" behind engine is result of oil and water being forced through the back seal of the turbo. That will dry out and splatter around the turbo and on top of the tranny. This is common in a Cummins 4BTA and 6BTA, and not viewed as a big issue. The way the turbo seals are designed, it will pass small amounts of oil and water that accumulates on the cold side of the turbo and eventually is noticed in the bottom of the turbo.

If the cold side of your turbo looks like this photo I took at the end of a season a few years back, it's a normal accumulation of oil in a Cummins turbo (per Tony Athens, Seaboard Marine, boatdiesel.com). Periodically cleaning your air filters and the turbo itself will eliminate or minimize the accumulation in the turbo. There are detailed instructions on cleaning the cold side of the turbo on boatdiesel.com.

HOWEVER... your started your thread with... "So we overhauled a Cummins 6TBA 5.9-M3", so I guess the "dust" you see could be just about anything.
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