DD 6v92 problem

I’m running a pair of DD 6v92TA Covington conversion engines making 435hp each. Engine year is 1979. Last fall I had my second injector problem of the season on the stbd engine, so I put in a full set of injectors that I got from Scrod. I ran her a few times in the late fall, and again this spring with good results.

This past Sun I headed out to go fishing and after 5 minutes of running (2050rpm) that engine bogged down and billowed out black smoke. After that it would only run up to about 1300rpm without smoking. I checked the turbos and they seem to be spinning smoothly. Does this sound like an injector problem to you guys or do you think I have something more serious? BTW, engine did not overheat, and oil pressure is fine.

Sounds like lack of air flow (turbo), but I'm no expert.

That sounds like an airflow problem -- are you sure you didn't lose an airhose somewhere between the turbo and airhorn?

I looked for hoses that might have slipped and saw none. I just spoke with a local "old timer" DD guy whom I respect, and he tells me that just spinning the turbo by hand may not tell me one is bad. Apparently sometimes you have to push in and spin to find the problem. He also said to look for excessive soot around the unit. I admit I only gave it a cursory look on Sun, so I'm going to give it a closer inspection tomorrow.

Dan rebuilds the units himself, and I do trust him, but if it is a turbo, what are my options to purchase re: cost and dependability?

If you could get me a part number off the turbo itself I can explore some options for you.

I'll try to find one tomorrow when I'm there. Would the engine s/n be of help? BTW, are the two (inboard and outboard) turbos identical or is there a "left" and a "right" turbo?

Your mechanic is right. It's what they do when running that matters. It does sound like a bad turbo. Get Derek a part number and see what he comes up with. The turbo can vary from year to year and between marinizers.

Check the emergancy air flapper is not open or stuck halfway.

No air flapper on 6V92TAs that I've seen from that vintage. (Twin-turbo dry models) There should not be any soot around the unit; pull the blankets (cold engine only!) and have a look.

What you're describing is a sudden failure rather than a slow degradation in performance so the problem should be pretty readily apparent on close inspection. If the turbos look ok one thing to check that is rare but possible is a collapsed baffle in the exhaust that is partially blocking it. Does exhaust flow look and sound the same on both sides at the dock?

If the engine runs normally up to the 1200-1300 range its probably not a fueling-related problem (e.g. injectors, etc) and is much more likely on the air side.

Blower? Air door shut down? Turbo bad? It sounds like something let loose or stopped the air flow. Check the air intake path and see if there is a blockage.

Look on the exhaust side of the turbo. Carbon can build up and when loaded make the turbine drag. Slower turbo, less air, same amount of fuel, black smoke, no rpm.
Bob

Thanks for the suggestions, guys. It was a sudden failure. One minute running fine and the next minute billowing black sooty smoke and immediate engine degradation. Dropped from 2100rpm to 1400 almost instantaneously. Correct as usual Karl - no airflaps on these engines. I kind of doubt an exhaust blockage because it came on so suddenly.

I did immediately suspect turbo, but I wondered if a blower could fail suddenly and cause the same symptoms. I don't know how to analyze a blower failure.

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Originally Posted by Bob Bradley

I'll try to find one tomorrow when I'm there. Would the engine s/n be of help? BTW, are the two (inboard and outboard) turbos identical or is there a "left" and a "right" turbo?

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I had a pair of them witches in a 45c 535 hp black smoke is as all have said generally air at least smoke of that magnatude. If it was hase at 2000 then look for injector problem or the beginning of turbo going out. Sometime on hase smoke just open the inspection hole in the bulk head it will clear up some.
As for the turbo good or bad issue. Take the insulation off remove the air cleaner put your hand in the turbo and not just spend the blades but rock side to side if it is loose at all it is done. Also while you are bying get your self a spairs. Three years ago they were on national backorder. Be ware of off brands they are sometime not up to speck and will smoke at best. I spent tuns of dollars on turbos till i got smart and bought new ones not rebuilt. Get them fron a DD guy if possible make sure they are oem. I got angry put four new ones in and slane vents and still had a little has had to look closs for it though and only on a calm day till you got back to the dock and looked at the stern. Them engines are going to smoke for several reasons air,under a load, not proped correctely, bad weather up and down waves putting the boat in a strain.
I would run off shore they called me smokey I was never able to get the haze competely gone. Good luck
In short i would say you gotta turbo issue... DO NOT RUN THE BOAT UNDER THE EXTREME SMOKE CONDITIONS SOOT IT ABSOLUTELY THE WORST THING A ENGINE CAN SUCK IN.... TIM

Fuel Shut down solenoid partially closed? Thx

Im betting on the turbo or airfilter clogged.

did you change fuel filters?
I always check the simple stuff first, filters (fuel and air)

a stuck injector will aslo cause lots of smoke and loss of power

Is there any chance you fowled one of the wheels with some rope or something?

I once picked up some crab pot warp and had very sudden loss of power and some slight vibration.
it wasnt until a went under the boat and saw a birds nest of rope around one of the wheels.

Just got back from the boat. It's a turbo alright. Inboard turbo on stbd engine is toast. Fins were all chewed up and there was considerable play in the shaft. I spoke with Derek (Scrod) just now and have a shiny brand new one on the way for early next week.

One week down one new turbo not to bad could have been worse :p
It could have happened 80 miles out!
Good choice going to Scrod.

That'll do it.

Ok, now on the R&R, here's how you avoid making more work for yourself. ;)

Get a can of PB Blaster. And bring PATIENCE to the job.

Remove the monmon clamp (exhaust side to crossover pipe) and DISCARD. Do NOT re-use; if you do it may break while under load and spew 1,000F exhaust into your engine room -- this is a really good way to have an engine room fire. Remove air side (hoses and air filter.) Remove oil return pipe, make sure the return pipe it's unobstructed, remove oil feed hose. Make sure no dirt or debris goes into the oil feed hose.

The exhaust flange from the hotpipe is bolted onto studs. The bolts are self-locking castellated nuts and love to seize on the studs. Spray liberally with PB Blaster and attempt to break them free. Use care removing these nuts. Specifically, DO NOT USE A BREAKER BAR -- you will break the stud! Take your time and soak with more PB as required -- if it takes a couple days of spraying it every couple of hours and rapping the side of the nut and flange lightly with a hammer to break adhering rust, do it. They'll come off but it takes patience. Discard the old castellated nuts and replace; stud replacement is usually not required but if questionable you may want to. They're lots of fun getting out of the hotpipe if one or more are damaged, by the way -- same deal as the nuts on removal.

If you break one or more of the studs you're left with a tough choice. It won't come out generally if that happens (e.g. drilling the center and attempting to use an easy-out is asking to break THAT, which compounds your problems), which means you'll have to try to drill it out and then use nuts and bolts afterward. And the hotpipe is cast iron, by the way, which means the odds are good the flange will break when you try this. That's to be avoided (you get to buy a new hotpipe if it happens and they can be tough to find) But IF you get yourself in that position and manage to drill out the broken stud Cat makes a set of nuts and bolts for this purpose that are intended for turbo mounting, heat-rated and a better choice for the future. Hope you don't have to go there.

When you get it apart check the flange on the output side to make sure it's true (on the exhaust collector) and that the flange on the hotpipe is undamaged. Check for any foreign objects, especially since you had the previous turbo grenade, so you don't wind up with a piece in the new one and blow it up immediately.

VERY IMPORTANT: When hooking up the oil lines fill the inlet side of the turbo with clean oil from a new, unopened container before attaching the line so you're not starting the engine without lubrication in the bearing, and hold the STOP button on the engine when cranking the first time for 30 seconds or so to make sure the oil line is filled before you allow the engine to start. And of course don't run the engine with the turbo blankets off under load as the exhaust side gets extremely hot.

That should do it. If you take care to never shut down the engine without allowing the turbos to cool off first (idle until EGTs are nice and cool; if you don't have EGT gauges then no less than 5 minutes after coming off load) you'll avoid what usually blows these little turbos up -- coking in the center bearing from hot shutdowns.

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Originally Posted by 34Hatt

Good choice going to Scrod.

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I thought so. :D

We appreciate the business. Thank you Bob.

If I had patience I'd have been a farmer.

Seriously, thank you Karl (and everybody) for the sound advice. It's a good feeling to know I can count on you guys when the kimshee hits the fan.

I gave all the fasteners a good soaking with PB this afternoon when I was down checking it out. I didn't have my full toolset with me (forgot it at home) so I didn't succumb to the temptation to start the removal process beyond that. Since I have 4 or 5 days to wait until the new one comes in, I'll hit it a couple more times with PB and AeroKroil before I really have at it with the wrenches. Worst case, I have a turbo torch with MAPP gas that usually will get the job done.

The new unit does not require that I send in the core, so I may have the old one rebuilt as a spare to keep on hand.

Can you replace just the turbo cartridge or do you need to replace the whole thing on those little ones? Rebuilding for a spare would be good to have if one goes and you are away from home.