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.