Failed Starter on 312-8

[FDSJr 3]

I believe that the starter has failed on my 312-8.  The battery is good and fully charged and the starter solenoid works fine.  I have full battery voltage on the cable that runs from the solenoid to the starter positive terminal when the ignition key is turned to start.  But, the starter will not operate.  In fact, if I run a cable directly from the battery positive to the starter terminal, the starter still will not operate.  The diagnosis here seems pretty obvious -- the starter has failed.  Is there anything that I might have missed in the failure analysis?  I ask because this is a new starter, installed only 2 months ago and has been working fine since installation.  The thing died on me a couple of days ago.

[Ed Kennell 35,592]

The only thing left … is the starter grounded?      Reconnect your 12V to the starter post, then add a jumper from the battery - post to the starter housing.

[wallfish 15,905]

Loose or corroded ground connection(s) or wire(s). Does your ground cable go directly from the - battery post to the engine? Or to the frame? Are they clean tight connections?

Do as Ed suggested, use a set of jumper cables to eliminate wire or connection issues as the culprit.

Could the bendix gear of the starter be bound up on the flywheel?

[FDSJr 3]

I unhooked the battery cable from the starter.  I checked the resistance between the battery negative post and the starter housing to see if there is good continuity.  The reading is 2.0 ohms.  I also checked the resistance between the battery negative post and the starter terminal.  The reading is exactly the same -- 2.0 ohms.  I could be wrong, but I would guess that the resistance of the starter windings should cause a higher reading between the starter post and the battery negative (ground).  Maybe there is an internal short in the starter.  I will try your suggested test and see what happens.  

[FDSJr 3]

Thanks to both Ed and Wallfish for the suggestions.  The battery negative connects directly to the frame and the starter housing is bolted to the engine.  I will proceed with all suggestions on testing before I pronounce the starter as dead.

[squonk 38,844]

4 hours ago, FDSJr said:

I unhooked the battery cable from the starter.  I checked the resistance between the battery negative post and the starter housing to see if there is good continuity.  The reading is 2.0 ohms.  I also checked the resistance between the battery negative post and the starter terminal.  The reading is exactly the same -- 2.0 ohms.  I could be wrong, but I would guess that the resistance of the starter windings should cause a higher reading between the starter post and the battery negative (ground).  Maybe there is an internal short in the starter.  I will try your suggested test and see what happens.  

Be aware that low resistance in a cable does not necessarily mean its good.You could have 50 strands in a cable and 49 broke and still get a low reading. I would pull the starter and bench test it. It does sound like it failed. I would change the cables anyway seeing  as how old they are and your into it . I change all my cables if it's a new machine to me or they get about 10 years on them.

Edited May 28, 2018 by squonk

[FDSJr 3]

Just a final follow-up.  After all electrical cables and connections were "renewed" and the starter solenoid & ignition switch checked for good operation, the starter still would not turn over.  I removed the starter and found that it worked just fine when not attached to the engine.  Apparently, as was mentioned in an earlier posting by wallfish, the Bendix gear engagement with the engine flywheel was the problem.  It was a mechanical issue -- not an electrical one, as I had initially assumed.  The starter is back on the engine and all seems to be working well again.  Thanks to everyone for the suggestions.