Cummins 785 and Cummins 903 compatibility

[NCFordMan]

Hiya Sam’s group! I have a 1970 53 MY with the Cummins 785s / V-370s. They are running ok, but major oil leaks. Stb side is blowing some smoke. I’m contemplating a repower. I believe the Cummins 903 is a very similar block and heads. Curious if anyone knows whether the 903s would be a fairly straightforward replacement. I could also do an in frame rebuild of the 785s, but the parts are very difficult to locate and expensive. Plus, I’d enjoy the additional HP and torque from the 903. Thoughts? Is the 903 a reasonable option?

[Retired1]

Hiya Sam’s group! I have a 1970 53 MY with the Cummins 785s / V-370s. They are running ok, but major oil leaks. Stb side is blowing some smoke. I’m contemplating a repower. I believe the Cummins 903 is a very similar block and heads. Curious if anyone knows whether the 903s would be a fairly straightforward replacement. I could also do an in frame rebuild of the 785s, but the parts are very difficult to locate and expensive. Plus, I’d enjoy the additional HP and torque from the 903. Thoughts? Is the 903 a reasonable option?

“sbmar.com” the Cummins repower experts

[SeaEric]

IMHO If you can find a mechanic that knows the VT370M engines (and he's not in a wheelchair) it makes sense
to trouble shoot repairing the engines you have. If you decide to invest in the logistic of a re power, it
would be best to go with modern power. A 903 is just a newer dinosaur than what you have. BTW where is your boat located?

[NCFordMan]

It’s in the coastal South Carolina area.

[whoover]

903 parts are hard to find too and are also expensive. If you are going to the trouble to replace get something modern in there.

Walt Hoover

[cww]

I'm very familiar with this topic having been a longtime Chris-Craft Commander 47 owner, those were the single biggest customer for those Cummins VT-370's. In the Chris-Craft world boats with the 370's are getting rare, they have mostly all been replaced at this point because of parts unavailability. When one comes up for sale, it usually sells at a steep discount over a boat with Detroits or some other engine. There have been no parts available for 20 years now, it's extremely unlikely that you could even find the parts to rebuild them. The probability is close to zero.

I don't think you have any real option if you're having issues but to replace them at this point. I would not go with another Cummins that's only slightly less difficult to get parts for, I would go with something new enough that you can get parts for the foreseeable future. These aren't like Detroits where you can still run 40 year old engines because they have factory parts support. That's the exception, not the rule. Cummins is pretty bad about cutting off support earlier than most. They're even worse on the generator side, I have had friends who couldn't get parts for a 10 year old Onan genset.

[warrenw]

I agree with Chris that the Cummins VT8-370Ms are now a liability as parts haven't been available for years. I repowered my Chris-Craft 47 Commander from twin VT8-370Ms to twin Caterpillar 3208TA 375hp. The previous owner tried to find liners etc. for the port VT8-370M with no luck. I purchased the boat from him after it sat covered on the hard for 9 years. The VT8-370Ms were apparently difficult to find parts for years ago, I know a guy that has a 47 Commander like mine that was repowered with Caterpillar 3208TAs in 1988! The 903s are more common due to military applications but in some boats like mine, they were just different enough they don't fit easily.
My suggestion, if you are up for repowering and on a budget find a good set of used Cummins C-series, Caterpillar 3208TAs or maybe more modern engines from these manufacturers if you stumble across a deal. Otherwise just continue to baby those old Cummins and keep your fingers crossed.