Cummins 6BT 210 hp rough idle

I recently bought a 1987 Shannon 32 Brendan with the original pair of Cummins 6BT 210 hp engines with just under 1200 hours. The port engine idles is rough and vibrates more than I'm used to from idle to about 1200 rpm. The starboard engine runs smoothly. Someone had also put a container to catch oil from the ventilation tube and there was about a pint in there. Don't know how long that took to accumulate, will be keeping an eye on that.

Any thoughts or similar experience and how was the problem solved? Thanks!

Photo of our boat since 1966 "Spindrift" and the Shannon "Plover" together.

Cummins are famous for blow-by but a pint? Have you run them hard? Do they smoke? How long do you let them idle? The book says 5 min MAX. Do they make WOT? What did your surveyor say?

Glazed cylinders? Valve adjust? Blown turbo? Bad injectors? Clean fuel filters? Clean coolant filters? Good coolant additives? Good fuel? They should just be getting broken in but maybe they were abused/not maintained/idled too long?

Might need some more information.

I recommend you sign on to boatdiesel.com. The experts there are great. You will get the best input there. Tony Athens has helped me in the past.


I have two 1988 210 6BT5.9Ms. They have almost 3800 hours and produce almost nothing from the vent. I replaced the "puke bottle" with the polished aluminum vent can in the picture. The picture is the day I installed it. Later I had to remove the brass plug on the left side of the can. The filter eventually loads up due to oil mist and creates minor back pressure. By removing the brass plug it breaths and still contains any vapor.
RUN SEE MIGHT SHINE SHE MUST!

The pint was in the container when I bought the boat, on the hard, a month ago. Launched Plover on August 31 and ran her to a mooring 45 minutes away at 1200 rpm (9 knots). Then ran her home, 6 hrs., roughly 2 hrs @ 1200 rpm and 4 hrs @ 2000 rpm. So, that's all the experience I have so far. I have not had a chance to look to see if there was any accumulation so far.

The exhaust transom mufflers so a little hard to see smoking. I'd say little to none. No smoke when cruising at 9 or 15 knots.

I have not done a wot test, yet. Really haven't had time do much. Looking to get a plan together as to what to look at and what order.

I do not know how the previous owner, an elder man, ran her during the 15 years or so of owner ship. Light cruising I'd say. From the folder of receipts, the oil & all filters were changed every other year (barely 100 hrs over that time). So, I'd say the engines were well maintained. They weren't afraid to spend money on her. She has a Racor filter ahead of the factory filters for each engine & the fuel looks and smells normal.

PenBayCruiser:

I strongly second posting this problem on boatdiesel. There are simple diagnostic tests that can zero in on the problem, but boatdiesel is a much better place to discuss them. There are world class marine diesel experts who hang out there. Trawler Forum has boat owners.

David

djmarchand said:

PenBayCruiser:

I strongly second posting this problem on boatdiesel. There are simple diagnostic tests that can zero in on the problem, but boatdiesel is a much better place to discuss them. There are world class marine diesel experts who hang out there. Trawler Forum has boat owners.

David

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Please loop back and tell us what you discovered

Thanks for the input. I've read about the boatdiesel site before. So, yes this would be good time to join.

I bought the boat very reasonable and have been a mechanic & engineer for several decades so did not use a surveyor. Ran the engines prior to making the purchase. They started almost instantly even though being fire for the first time since last fall.

Will up date my findings. May be late this fall or spring be I have time though.

Thanks again!

If the records are incomplete, I would use the Cummins manual and do the 1000 hour maintenance routine. I believe it is all filters, oil, valves, coolant, injectors, check the intake for cleanliness, etc. What the manual says. Give yourself a baseline. Then you have something to take to Boatdiesel (I belonged for a year and won't go back, I got fed up with the restrictions on membership and the continual requests for more money. You can have it).

I am a bit surprised at your boatdiesel woes. I have been a member for ten years. I started as a Level 1 member at a cost of $25 per year. That level gave me access to most everything I really needed, but did have limits on pdf library downloads and did not give access to the advanced prop calculator or the on-line library viewer.

The next level at $50 per year gives me unlimited pdf downloads and access to everything.

Boatdiesel is a highly technical web site with professionals in most marine diesel families offering advice for free, an extensive library of engine data, calculators to help with engine and prop sizing, all of which takes effort. It has paid off handsomely for me.

David

djmarchand said:

I am a bit surprised at your boatdiesel woes. I have been a member for ten years. I started as a Level 1 member at a cost of $25 per year. That level gave me access to most everything I really needed, but did have limits on pdf library downloads and did not give access to the advanced prop calculator or the on-line library viewer.

The next level at $50 per year gives me unlimited pdf downloads and access to everything.

Boatdiesel is a highly technical web site with professionals in most marine diesel families offering advice for free, an extensive library of engine data, calculators to help with engine and prop sizing, all of which takes effort. It has paid off handsomely for me.

David

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??????? what woes????

Xsbank said:

I belonged for a year and won't go back, I got fed up with the restrictions on membership and the continual requests for more money. You can have it.

Click to expand...

Not your woes, Xbank's.

David

I also have a pair of the Cummins 6BT's, mine are the 165HP's. Did a top end at 12,000 hrs as preventative maint. and now they have 14,000 hrs on them and still run fine, always run at 1800RPM.
Yours, with 1200 hrs are due for injectors. I'm NOT saying this will clear your problem, but it might be an issue. I generally change mine between 1000-1500 hrs depending on my schedule and it's usually a noticeable difference. It's an easy change, I made an injector pulling tool to fit on a slide hammer to pop them out, always use new copper seals under the injector and on the return line banjo fittings.
Tony Athens on BoatDiesel is an expert on these motors, but, always next to impossible to diagnose problems on internet.

First thing to check is at idle pull oil fill cap and watch carefully the blowby flow with a flashlight. If it is puffing, there may be one hole with poor compression. Should be a steady wafting of vapor coming out.

Next, crack each inj fuel line nut one at a time and see that rpms and sound note changes with each loose nut. If idle is unstable, do this test at lowest stable rpm.

Go from there.

BerettaRacer said:

I also have a pair of the Cummins 6BT's, mine are the 165HP's. Did a top end at 12,000 hrs as preventative maint. and now they have 14,000 hrs on them and still run fine, always run at 1800RPM.
Yours, with 1200 hrs are due for injectors. I'm NOT saying this will clear your problem, but it might be an issue. I generally change mine between 1000-1500 hrs depending on my schedule and it's usually a noticeable difference. It's an easy change, I made an injector pulling tool to fit on a slide hammer to pop them out, always use new copper seals under the injector and on the return line banjo fittings.
Tony Athens on BoatDiesel is an expert on these motors, but, always next to impossible to diagnose problems on internet.

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WOW! 14000 hours. That's great, do you buy new injectors every 1000-1500 hrs? What is the cost? The PO of our boat had injectors done at 2000 hrs but I think they were just ultrasonically cleaned.

Yes, fresh set at each change, can't remember if new or remans, and don't know the cost, billing goes thru the office.

BerettaRacer said:

Yes, fresh set at each change, can't remember if new or remans, and don't know the cost, billing goes thru the office.

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I have one spare injector that I paid $145 with a $45 refundable core charge. It would be $1200 to swap out the 12 on our two engines.

Beretta

Assuming you have clean fuel, your injectors should easily go for 5000 or more hours. Especially with engine loafing along at 1800 RPM. Just curious, who advised you on a 1200 hour changeout?

I had in mind taking the injectors to a shop, had good success w/a local shop, for a checking over or rebuild. That would also be a good time to check the compression. Checking for blow by is a good idea, Ski in NC, before doing either of the above. A Cummins manual fortunately did come with boat so I need to spend more time studying that as well.

Like I said earlier and you agreed but haven't done it yet, is to post this problem on boatdiesel. Ski is an engineer/mechanic. Most of us on this forum aren't. You will get much better help (not that there was anything wrong with Ski's advice above) on boatdiesel.

David

sunchaser said:

Beretta

Assuming you have clean fuel, your injectors should easily go for 5000 or more hours. Especially with engine loafing along at 1800 RPM. Just curious, who advised you on a 1200 hour changeout?

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5000 hr injectors on my Cat 3512's yes, they're full body mechanical injectors, long service life.

Cummins 6bt, no.
Cummins factory reps did this install back in mid 90's, we were a test bed for the factory at the time, (don't ask, long story). Initially they were hoping for 1500 hrs, but by 1200 you could begin to see a sheen from the exhaust, and that became the standard.

Remember, the 6bt is basically Chrysler a truck engine.
1800 RPM = 60 MPH
60 MPH x 1200 hrs = 72,000 mi if in your truck

My engines @ 14,000 hrs x 60 MPH = 840,000 mi

(On a different boat, back in 86-87, I was the test bed/instruction demo boat for the MTU TB396, got full MTU factory service for cost of parts only, LOL)

Very helpful information. Thanks for the input!

Must be starting to get a little chill in the air in Camden. I grew up just southwest of you a bit, spent time both on the coast and inland lakes. Learned how to sail out of Freeport area/Casco bay, but have cruised the coast off and on over the years. Left Camden Hbr the day before hurricane Bob back in I think 92, that did a lot of damage there. Spent a month or so bouncing between Portland/Boothbay/Camden/Bar Hbr. six yrs ago. Then five yrs ago just did a fuel/food/weather stop in Portland on way both to and from Halifax/ St Lawrence /Great Lakes.

I'm sure Tony on BoatDiesel, or on his shipyards website SBMAR.com has a few tests you can perform to help define you problem, max allotted blowby/crankcase pressure, maybe an adapter to do a compression test. Like someone said earlier you can back off one injector at a time, sometimes helps but messy, make sure you got plenty of diapers for the fuel runoff.
On Youtube there are vids on how to make an injector puller, I think I used an old fuel fitting and had it welded to a slide hammer fitting.

This is the first chilly day actually, been very warm & humid. Funny you should mention Hurricane Bob, we were camping on Warren Island the day before.

I'll have to check out that video. Expect to pull the injectors and have Atlantic Fuel Injection go over them. Plus like to run a compression test.

Check the blowby already. Just takes a flashlight and pulling oil fill cap. And do the inj cancel test, just takes a wrench and a rag.

Check the engine mounts and if suspect, the engine alignment. Is it really rough or is it rattling? Could be the damper plate? The crankshaft dampener can cause roughness when it fails.

Change the fuel, oil, coolant and air filters. Set the valves. Check the coolant condition. With the air filter off, look at the turbo for damage and leakage. Pull the intake pipe and clean out all the crud. NOW run the engine and look for blowby (they all have some, especially the engines that are not mounted horizontally fore and aft. If you are not familiar with Cummins, this may not tell you anything). Still rough? Now pull the injectors. Remember to replace or anneal the washers when you put them back. Does the manual say to check the timing now? Do that too. Now do a compression test.

Use a logical progression, get a baseline to ensure the engine(s) have been maintained, don't just start piecemeal. It might not be at all what you might guess.
Good luck.

Unfortunately the boat is 85 miles away. If I make the trip this weekend. 1. See if the engines will come up to full rpm. 2. Check the blow by. 3. Time permitting, pull the injectors to bring back with me. Air filter is clean. Oil, oil filter and fuel filters changed at the end of last season.

I've been up to the boat a few times over the last month. Could have swarn the port engine was rough but it's the starboard. The port engine did have a little smoke at idle at operating temperature. Also, found a report discussing these issues from a couple of years ago.

Have done the following; 1. Opened oil fill caps, no appreciable blow by. 2. Engines reach max rpm (2600). 3. Cracked injector lines, each created the same sounded and effect to idle.

Decided to have the injectors checked out. Only had enough day light to pull port engine injectors. The shop said they were working well but showed wear upon being disassembled. Cost to rebuild $120 ea, new Bosch units $90. Decided to buy the new ones. Not only less expensive but start our ownership with new.

Installed the port injectors last weekend before going out for cruise. The little bit of exhaust smoke has cleared up.

Hope to swap out the injectors in the starboard engine next weekend.