starter problem

One of my starters on my 671 Detroits won't kick in. It is only 3 years old. Had a new one put on 3 years ago. Don't know why but the diesel shop that put it in put in a Cummins starter. My original starter that's 30 years old on the other motor still runs fine. Any help is appreciated. We jumped it once and it kicked in a few times, then stopped working again. could it be the solenoid?

The Cummins branding is probably because it is a DELCO core that Cummins rebuilt. I don't know. But, if it's been working for three years you first need to do some checking before worrying about if the starter or solenoid is bad.

I think you should shut off the battery switches and then remove and clean the cable and wire connections at the starter, solenoid and the shut off switch before jumping to the conclusion a component has failed. Also, it is a good practice to disconnect the cables at the battery and clean the ends to the shut off switch and the battery terminals.

With your engines not starting, have you been doing a lot of cranking? Those starters are not designed to take a lot of heat from extended cranking. 20 seconds MAX and then a good long cool down between cranks if you want them to live a long time. Also, make sure you are not backing water into the cylinders through the exhaust if you are doing a bunch of cranking with the sea cocks open. Many marine engines totally destroyed that way.

If, after cleaning the electrical connections, the starter still won't crank, there should be a big metal plug on the end of the solenoid housing with a recessed "cross" in it. Under that plug is the solenoid contact lever. You can use a large screwdriver or a punch and hammer to turn the plug counterclockwise and remove it. Then, you can insert a screwdriver or a big punch in there to push the lever forward and see if the starter will engage and crank the engine.

MAKE SURE ALL PERSONNEL ARE CLEAR OF THE ENGINE!

If the starter motor will then crank, you probably do have a bad solenoid. If not, then the starter motor itself is shot.