6bt overheated

I did a completely bone-headed thing and ran my motor with the seacock closed until the coolant boiled over in large quantities. This is in my Mainship 34 with a 1991 Cummins bt6 210 hp. The motor was rebuilt about 1200 hours ago and has been well maintained since, with new belts and hoses, rebuilt water pump, etc.

The overheat happened in June and I pressure tested the cooling system, didn't see any obvious signs of damage apart from some burnt paint on the exhaust manifold, checked the oil for obvious signs of water, and carried on.

I've noticed a very small amount of coolant loss since then, but more ominously now have a lot of blowback from (I think) one cylinder, and oil accumulating in my CCV puke bottle, maybe 10 oz in the last 100 hours since the overheat event. The motor starts and runs fine but is rough at < 1000 rpm, particularly under load. Sounds like it's not running on all cylinders. Oil consumption hasn't been excessive.

Getting ready to lay up the boat for the winter here in Ontario and considering my options. I think I'm going to pull the motor and transmission out of the boat, and feel comfortable tacking that myself.

Much as I like tackling problems in a DIY manner, I think I'm going to need to rely on professionals for a resolution. I sort of budgeted for this sort of thing, but don't like spending more than I have to. But I think this boat is a keeper and I plan to travel far and wide on it so am interested in a proper fix.

Options:
1) find a local shop and leave the motor with them. I'm assuming that the exhaust manifold will need to be replaced in addition to the usual work on the block, pistons and possibly head. I'm thinking that because the Cummins is so ubiquitous it wouldn't have to be a marine shop.
2) replace motor with a rebuilt/remanufactured one.
3) there is a local 6bta 250 hp marine for sale that's never been used at a reasonable price (us$12k for motor and transmission). The transmission on it wouldn't work for me because the gear ratio is too high, so I'd have to find a gearbox as well, but otherwise I think it could be pretty much a drop in replacement. I currently have a BW 72. Not really interested in going faster, but don't see much downside of having 40 more hp available.

I think #1 is the sensible and economical choice, but thought I'd throw it out for discussion here. Advice/experience/recommendations? What should it cost me to have my existing motor put into tiptop shape?

Nobody is going to give you much for your engine in it's current condition. I would find a good reasonable Marine Cummins mechanic and pull the head to see what you have. There are lots of 210s on Chesapeake Bay that watermen have treated far worse.

Ted

Wouldn't a compression test be worthwhile before pulling the head off?

High coolant temps don't necessarily ruin an engine. Quickly controlled, often no apparent damage occurs. Most high heat damage is usually in the rings and sleeves/cylinder.
A compression test or a leak down test can help you gauge the condition of the cylinder, piston, rings and valves.
Rough running could be many things. It could be as simple as a burnt injector tip.
Even putting in new rings would be cheaper than $12,000.
A non-marine engine usually has a different cam.

Run engine with oil fill cap off and take note of blowby flow. If "puffing" in sync with once cylinder firing, the rings on that cylinder are not sealing. In that case I'd plan on pulling the engine and going through it. A good first step is to pull head and that way you can assess cylinder condition. Also makes it easier to get engine out of boat.

I'd rebuild the one you have unless it is severely damaged. The 250 has issues yours does not.

I've seen head gaskets leak after an overheat, not sure a minor leak would show up on a compression test...

I would get a good mechanic on board first before you start pulling everything apart, I agree with OCDIVER.

Expanding a bit on the previous advice:


If you have little blowby, then the overheating event could be limited to a blown head gasket, warped head or cracked exhaust manifold, sort of in that order. Even in the worst case, all three could be repaired in the boat without pulling the engine, much cheaper than the other alternatives you are considering.


So, check blowby as Ski suggests and go from there.


David

If you currently (6bt) dont have an aftercooler dont add one. I dont know what other changes would be necessary if you removed the cooler from that cheap engine.

Why would your old trnny not work with the new engine?

IMO Ski's advice is good. Figure out what's wrong first.

Thanks to all for responding. The blowby is most definitely puffing. I checked this immediately after the event and it didn't seem to be an issue but it definitely is now.

So assuming I remove the motor, how important is it that I take it to a marine mechanic rather than a shop that does truck/industrial motors? I've been doing some preliminary research and there are lots of good shops in my area but very few that specialize in marine. Suppose I could ship it off, but don't mind doing some of the simple hands-on work myself.

Keep it coming!

The one marine specific component that the non marine mechanic wouldn't know how to deal with that might have failed is the exhaust manifold. But I think with a bit of guidance about how to pressure test it, he could deal with that.


Everything else: pistons, rings, cylinders, etc is common to marine and over the road diesels. But of course when it is all back together and doesn't work right for whatever cause, then what do you do? There will always be the excuse that it is a marine engine.


Does Cummins sell a short block for that engine? That might be a cheaper alternative, particularly if you have cylinder bore scoring that requires boring and oversize pistons.


Ski can probably tell you more.


David

"I've been doing some preliminary research and there are lots of good shops in my area but very few that specialize in marine"


There is a guy on the Baylinerownersclub that did two of these Cummins mostly himself by getting in rebuilds , they were done like 5 years apart or so- he is located east of Toronto likely not too far from your sig address. Here is a link to one of his more recent posts - perhaps ask him via BOC or PM him at the BOC - easy to register.




Bayliner Owners Club - BOC Forum - Topic: Twin Cummins 270B's (1/1)

pull the injectors and bore scope it and look for 4 point scoring.

Jeff F said:

Thanks to all for responding. The blowby is most definitely puffing. I checked this immediately after the event and it didn't seem to be an issue but it definitely is now.

So assuming I remove the motor, how important is it that I take it to a marine mechanic rather than a shop that does truck/industrial motors? I've been doing some preliminary research and there are lots of good shops in my area but very few that specialize in marine. Suppose I could ship it off, but don't mind doing some of the simple hands-on work myself.

Keep it coming!

Click to expand...

Little over 1,000 Km (11 hours) from London, ON to T & S marine in Crisfield, MD. Put the engine on a pallet; in a small enclosed trailer; hook it to the family land cruiser; grab the wife and take her to Florida (by way of Crisfield) for 2 weeks. Pick it up on the way home.

What's not to like?

Ted

Nothing terribly unique about a marine B motor. Anyone who can build a truck or industrial B can build a B210.

"So assuming I remove the motor, how important is it that I take it to a marine mechanic rather than a shop that does truck/industrial motors?"

I prefer a machine shop that also does work for racers.

They can balance the reciprocating parts far better than "factory" specs .

Just be sure to give them DA Book , (the factory service manual) and tell them the usual cruise RPM area.

The real fine ones will CC the cylinder heads and other refinements.Cam timing height and lift,, crank timing etc.

A good used block will stay in shape after line boring and other machining better than a factory green unit.

Your rebuilt should have longer life than factory new .

Depending on the CPL number you can buy a long block with tin for under $4000 US and put all your rebuilt peripherals on yourself. I am the guy Smitty was referring to and I did most of the work myself and jobbed out the rebuilding of the injector pump and several other items like craning it in and out.
I was fortunate that I could rent space in a marine mechanical shop and do most of it myself.

Jeff,
It's an old trick that has been mentioned here before, that if you hang the key on the seacock handle every time you shut it off, you will never forget to open it.
I always close the seacock when I'll be absent from the boat for more than a few days, and so far this method has worked well for me.

Good advice. I actually leave mine open at all times. But I was crawling around the engine compartment the night before changing filters and fixing some of the wiring and didn't realize I had inadvertently stepped on the seacock and closed it. One of the outstanding issues had been the temperature sender, and I had been religiously checking temps with my temperature gun in earlier trips, and all had checked out fine. When I went out the next morning I was busy checking other things until the cabin filled with steam... Completely user error

Another case for a rock-solid reliable audible temp alarm. Factory Cummins alarm is sketchy at best, best to rig your own.

The Other Gary said:

Depending on the CPL number you can buy a long block with tin for under $4000 US and put all your rebuilt peripherals on yourself. I am the guy Smitty was referring to and I did most of the work myself and jobbed out the rebuilding of the injector pump and several other items like craning it in and out.
I was fortunate that I could rent space in a marine mechanical shop and do most of it myself.

Click to expand...

Gary, I've read your account of that (twice!) on the Bayliner forum. I like the idea of doing pretty much exactly what you did. It will give me something to do over the winter

I want to take the opportunity to get more intimately familiar with my motor, and AFAIK the turbo, injection system and other peripherals are in fine shape. I also have a slight leak in the rear seal of the transmission so can address that as well.

Now I'm into the usual project scope creep problem - maybe while the motor is out I should also replace the fuel tanks...

For anyone contemplating doing a rebuild vs. a Long Block this was my cost in Canadian dollars. I have no special skills other than the fact that I do my own maintenance on all my boats.

Just to answer any questions

The following is all in Canadian dollars including tax

New long block from Cummins $5200 delivered
Rebuild injector pump and injectors $1750
New Turbo, I had one in my spares
Heat exchanger and transmission cooler servicing $250
Haulout, blocking pressure wash and relaunch $625
4 hours crane, 2 trips at 2 hours $500
Shop time $800, includes setting up and timing injector pump and stand startup
Oil, filters and antifreeze $165
mechanic and helper for both removal and install 8 hours total $1200
impellers, sensors, paint and misc. parts $250
My time 26 hours, a gash on my head and numerous bleeding knuckles , PRICELESS

Total $10,740 CDN
For a 5.9BTA Cummins with all new or completely reconditioned parts plus I now have a spare
starter, turbo, raw water pump, alternator and solenoids to keep on board.

As a comparison a new Recon from Cummins is $22,000 US plus shipping, duty/taxes and installation, $35,000 CDN approx.
and a used (850 hours) one from Tony Athens was going to cost $15,000 US plus shipping duty/taxes and Installation, $24,500 CDN approx.

I am tired, sore in body parts I didn't know I had but pleased with the weekends work.

Things I learned:
The tool list supplied in the manual is good for everything EXCEPT removing the starter, this requires a 10mm 12 point socket instead of
a 10mm 6 point socket. If you don't have one in your tool box, get one and tag it for starter removal.
To get the engine out the door without damaging or removing any upholstery.
Remove the heat exchanger, aftercooler, alternator, pressure tank, throttle linkage and the return line check valve.
Remove the motor mount bolts from the stringer flanges then lift the engine and lower back down onto 2 2x8 boards set across the stringers. Now you can remove the motor
mounts from the block and transmission without changing the mount settings ( tag port and starboard so they go back the same way) and the engine is
skinny enough to go right out the door if you remove the door travel stops so it will open that extra two inches.
Assembly is the reverse and the alignment was perfect at the transmission to prop shaft flanges doing it this way.

Good work Gary. What is your background that allowed you to jump in the middle of this effort? Again,

No real background other than backyard mechanic since my teens. I am a salesman in the real world for a medium sized new home builder. Ever since I have been boating I have been aware that there is no one to help you in a breakdown "out there" so I learn as much as I can about my boat and always have the manuals for any engine I have.

Glad to hear it is all done! I'm also a backyard mechanic since my teens (plus a few years working at a dealershipt), then I decided to go to grad school. Still do all the work myself (everything but bottom paint).

bayview said:

If you currently (6bt) dont have an aftercooler dont add one. I dont know what other changes would be necessary if you removed the cooler from that cheap engine.

Why would your old trnny not work with the new engine?

Click to expand...

I don't sense much enthusiasm here for the NOS 6bta option, but I haven't ruled it out yet.

- although 26 years old, never installed. Owned by a marine mechanic and run from time to time on the bench.
- have been thinking about transmissions and would be comfortable using my existing VD 72. It's a little light for this motor, but I'm really not interested in going fast. I would not change my prop, and would be a little underpropped with the 6bta (250 hp vs my current 210) but that's perfectly ok with me, given everything I've read about the B series.
- yes there is an after cooler but it's coolant cooled rather than raw water cooled, which makes it less undesirable I think.

So essentially I go to the bta but with no intention of taking advantage of the extra power.

I've read that one of the issues with this motor was the fuel pump being stressed at high power output, but again I think my usage would not call for high power.

Am I missing something? What are the objections? It would appear that this option would cost about the same as a comprehensive rebuild of my existing motor.

Thanks for all the comments.

Jeff F said:

I don't sense much enthusiasm here for the NOS 6bta option, but I haven't ruled it out yet.

- although 26 years old, never installed. Owned by a marine mechanic and run from time to time on the bench.
- have been thinking about transmissions and would be comfortable using my existing VD 72. It's a little light for this motor, but I'm really not interested in going fast. I would not change my prop, and would be a little underpropped with the 6bta (250 hp vs my current 210) but that's perfectly ok with me, given everything I've read about the B series.
- yes there is an after cooler but it's coolant cooled rather than raw water cooled, which makes it less undesirable I think.

So essentially I go to the bta but with no intention of taking advantage of the extra power.

I've read that one of the issues with this motor was the fuel pump being stressed at high power output, but again I think my usage would not call for high power.

Am I missing something? What are the objections? It would appear that this option would cost about the same as a comprehensive rebuild of my existing motor.

Thanks for all the comments.

Click to expand...

Edit:. 6bta is cpl 1247, my current is 742

There is no reason the NOS will not be suitable for your needs and it will save a lot of skinned knuckles. The velvet drive will be fine and it will all bolt right up without changes. New hoses may or may not be an idea and one of Tony's raw water pumps if it still runs the original Sherwood.

I bought the NOS 6bta



I have my old motor ready to pull in the next week or so and will use the existing transmission and running gear for next season so will definitely be underpropped, but I view that as a good thing. Will spend the winter replacing hoses and adding lots of sensors to the new motor (EGT, boost, temperature alarms) and cleaning and painting bilges in preparation for the new install. I may replace the fuel tanks as well. Kind of on the bubble on that, as I don't see any evidence of water intrusion or corrosion.

More to come.

Anyone looking for a 6bt that runs but needs a rebuild or a NOS Velvet Drive 10-26 get in touch. Think it's a 3.04:1 reduction gear.

Got my old motor out and sold it. I ended up making a lifting frame in the cabin and using rollers to move the motor back to the cockpit where it was easy to pick up with the backhoe. Now rebuilding my transmission, and will use the reverse process to get the new motor in once I have it together.