Looking for help with Cummins 6CTA (8.3 liter medium duty diesel)

[Skillet]

Engine is going into a friend's boat, supposed to launch him on Monday.  New engine from Cummins (factory recon), that was test run at their Tennessee facility.  He's doing a diesel-electric hybrid pilot project, pretty interesting stuff if you want to check it out (https://alaskapublic.org/news/environment/2025-12-23/were-really-breaking-new-ground-hybrid-fishing-boat-prepares-for-maiden-voyage-in-sitka). 

The crux of the matter is when we went to fire up the engine, the bendix gear slammed into the ring gear on the flywheel and wouldn't engage.  Based on the marks left behind, it appears this starter is not compatible with the ring gear (ring gear too "tall" to mate with the starter bendix, or the bendix gear is too large of a diameter)?  Cummins NW has said that they "sometimes" use a crank-nose starting tool to test run the engine before all the accessories like the starter, alternator, engine guards, raw water cooling systems, etc., are installed.  So there is a chance that the incorrect starter was installed after the test run...

Curious if anybody here knows these engines inside and out (or knows a pro that could identify and sell me the correct starter and fly it up tomorrow).  We have an SAE 3 bellhousing and flywheel, 159 tooth ring gear.  The starter is (I believe) a delco-remy 39MT.  It has a 12 tooth bendix gear on it, but I think we need an 11 tooth to reduce the OD of the bendix gear and get it to engage the ring gear?

So how about it folks - any of you medium-duty diesel engine guru's, or know of one in a truck parts shop I could talk to?

Thanks in advance-

Chris

[Fastass350]

I ran into the opposite when I put the last motor in my dump truck, it’s a big cam, 855. The bell housing I had took a small ring gear/flywheel setup so I had to change that out for the larger. Fast forward to installing a new trans with new clutch and new flywheel, they sold me a smaller diameter flywheel, when bolted up it was clear that the starter wouldn’t come close to connecting. Maybe it’s something as simple? Knowing what you’ll have to go through to change that all out I hope it is. Mine has the 39mt starter.

Good luck!

[Skillet]

Thanks for the info Chris...  I'm sure hoping it's something simple like that.  Decoupling this engine/gear combo inside the engine room is going to be low on my "that would be fun" list.

The Cummins NW rep has been getting me in touch with his guys this evening, so he's going above and beyond to make it right.  Hopefully we get to a solution soon.

[Fastass350]

I sure hope for your sake it’s something simple. Sounds like you got a good rep so that’s a huge win.
Something I just thought of, is it possible it’s the wrong rotation starter?

However it plays out keep us posted

[Skillet]

I sure hope for your sake it’s something simple. Sounds like you got a good rep so that’s a huge win.
Something I just thought of, is it possible it’s the wrong rotation starter?

However it plays out keep us posted

You know what, that is a possibility I didn't think of.  I'll check as soon as I get to the boat in the am.

[Skillet]

Update-

Our working theory is that someone swapped the flywheel out after it was test run somewhere along the way, but before it shipped to us... There is no starter available for this bellhousing/flywheel/ring gear combo.  I have to give Cummins NW props on their response, however.  They are airfreighting the correct starter/flywheel combo, and they are sending two techs (all on their dime) to help get this done tomorrow.

Boat is in the water now getting the electric drive stuff commissioned. As soon a they're done,  we tear it apart again...

Lots of valuable lessons learned on this project.

[pd]

Watching from the sidelines here.  I must say that Cummins NW impresses me with their response.

[EnglishSetter]

Sounds like you have a direction.

The only Cummins guru I know is Tony Athens at Seaboard Marine in SoCal.

www.sbmar.com.

Having pulled a 72C off a 6BT in the bilge of my 26 Shamrock, yeh, not fun.

What are you using for a flex plate?  I didn't want to ever do this job again, so went with a Suredrive hub.

https://www.suredrivemarine.com/suredrive

[Skillet]

They're using something similar to the suredrive, not sure if the brand.   It came from Italy.  That setup is pretty standard up here when you get into the 200+ hp continuous duty ratings.

As an aside, I put a suredrive in my own boat when Iput in a new gearbox for exactly the same reason you describe. Original setup was a damper plate, springs were broken. Had to have the folks at Suredrive custom build my hub center to match my oddball engine and gear combo (definitely not an of the shelf part). Expensive, but worth it.

[EnglishSetter]

They're using something similar to the suredrive, not sure if the brand.   It came from Italy.  That setup is pretty standard up here when you get into the 200+ hp continuous duty ratings.

As an aside, I put a suredrive in my own boat when Iput in a new gearbox for exactly the same reason you describe. Original setup was a damper plate, springs were broken. Had to have the folks at Suredrive custom build my hub center to match my oddball engine and gear combo (definitely not an of the shelf part). Expensive, but worth it.

Mine was 6BT to a Velvet drive 72C, so standard hub. Friends called it the flux capacitor damper.

Damper cam apart getting the splines out.

I'm curious on the hybrid set-up.  I've seen "get-home" set ups using a (petrol) pony motor driving a belt driven sheave on the driveshaft.  Wouldn't work for me as I have very little exposed shaft, but........

I know diesel electric is commonplace in ships and trains, but that's largely to let engines run where they're most efficient and let the electrics buffer the ups and downs.  So I'm not sure where this technology is supposed to (as in the article) cut fuel costs by 50-60% 

Now a nice Mr. Fusion on the other hand. 

[Skillet]

I know diesel electric is commonplace in ships and trains, but that's largely to let engines run where they're most efficient and let the electrics buffer the ups and downs.  So I'm not sure where this technology is supposed to (as in the article) cut fuel costs by 50-60% 

Now a nice Mr. Fusion on the other hand. 

Good observation, and I share your skepticism.  The main benefit that I keep hearing about is the ability to run under electric power during extended low power consumption activities - ie., slow speed trolling and hauling back most longline gear.  To be fair, this low power operation accounts for roughly 80% of my own boat's annual run time. However, I think the fuel saved by periodically running a 30kw genset at max efficiency to charge the battery bank (this is the main idea - run a smaller diesel more efficiently, less often) vs just idling along with a traditional main engine will be negligible.  The thing most often forgotten in these schemes is the power loss due to multiple energy conversions.  Going from rotational power to electricity, then back again to rotational power is accepting two large conversion losses.

I may be wrong about the overall viability.  Fishing styles, gear types, relative efficiency of the main vs genset at low power outputs, all come into effect.  There may be a situation where this makes a lot of sense.  I can't yet see it for my operation, or Jeff's.

However, if nobody ever experimented with technology, we'd still be sharing pics of our hunts on cave walls.

[EnglishSetter]

I know diesel electric is commonplace in ships and trains, but that's largely to let engines run where they're most efficient and let the electrics buffer the ups and downs.  So I'm not sure where this technology is supposed to (as in the article) cut fuel costs by 50-60% 

Now a nice Mr. Fusion on the other hand. 

Good observation, and I share your skepticism.  The main benefit that I keep hearing about is the ability to run under electric power during extended low power consumption activities - ie., slow speed trolling and hauling back most longline gear.  To be fair, this low power operation accounts for roughly 80% of my own boat's annual run time. However, I think the fuel saved by periodically running a 30kw genset at max efficiency to charge the battery bank (this is the main idea - run a smaller diesel more efficiently, less often) vs just idling along with a traditional main engine will be negligible.  The thing most often forgotten in these schemes is the power loss due to multiple energy conversions.  Going from rotational power to electricity, then back again to rotational power is accepting two large conversion losses.

I may be wrong about the overall viability.  Fishing styles, gear types, relative efficiency of the main vs genset at low power outputs, all come into effect.  There may be a situation where this makes a lot of sense.  I can't yet see it for my operation, or Jeff's.

However, if nobody ever experimented with technology, we'd still be sharing pics of our hunts on cave walls.

30kw = 40 hp with no losses.  I have to believe the losses will be substantial.  Electric motors can be torquey, but I'm expecting 10% loss at the motor and another 10% for charging + any rotational losses so we're down to say 30 hp at the prop.

I dunno what it takes to troll a 50' boat with gear set and of course that will be influenced by current and wind.  Just my WAG, it will take the genset running full tilt to keep up, which kinda gets me back to the "get home" pony motor to perhaps a clutch driven chain drive on the main shaft.  But nobody granted me 6 figures to come up with something better.

Keep us up on the project though.  It's interesting.