Starter will not spin

[NRbar]

I have a Ford Lehman 120 diesel. The starter selenoid clicks but won’t spin the starter. Engine turns by hand. Voltage to starter same as batteries at 13+. I took the starter to a shop. Works fine on the bench. I said let’s replace the selenoid for peace of mind. Back to boat and hook up ground wire and positive to starter. Spins like it should. Install starter and back qto click with no spin. Take out starter. Ring gear fine and turns when I manually turn engine. Hook starter up to the positive and negative wires it uses when installed. Works fine. Starter worked for years. What am I missing. I am in Fort Lauderdale and Ubering.

[hlev00]

It sounds like the starter is not getting enough power to overcome the resistance of the engine when trying to crank it. It doesn't need nearly as much to just spin when not mounted. Check the voltage at the starter when the key is turned to start. Likely you will find a significant voltage drop. The root cause is probably a degraded connection in the wiring, positive or negative, of the wiring going to the starter. Also check the path of wiring going to the solenoid. It is not unusual for an older boat to have degrading electrical connections that work fine, until they don't.


It could also be an aging start battery that can't provide need cranking amps.


Harry

[hpeer]

It may be the solenoid.

5he solenoid is just a relay, low current control circuit from switch causes the solenoid to click. So the control circuit is working.

However the POWER circuit passes through contacts in the solenoid. Those contacts can, with time, build up significant carbon pitting to not pass the required current. Thus the solenoid clicks but the starter does not turn.

The test is simple. Identify the hot/red wire to the starter. Follow it back to the solenoid. Then find the wire back to the battery. These are typically 2 pretty good size connection s on the solenoid. Now short out those 2 wires. Use a piece of wire, pliers, or a knife you don't care about. It may spark but the starter and engine should spin.

Then you know to replace the solenoid or look deeper.

[NRbar]

Harry
Thanks for the quick reply. I cleaned all the electrical connections, +&- . I tested voltage to the starter 13.4v, within a tenth of a volt of the batteries. The same voltage from the key switch to solenoid wire. I forgot a load test. I have to reinstall the starter to load test.
I had the starter to the repair shop. It worked fine on the bench. I asked them to go through it and replace the solenoid. I was in their shop for the bench test and break down of the starter.

I used the house bank to start the engine, three 8D batteries wired in parallel. The positive cable is newer and 2/O. The negative to the starter case is older however the engine ground is also newer. I have a newer 2/0 negative wire on hand and will replace the start case ground.

Hpeer thanks for the quick reply as well. I was defiantly worried about the solenoid contacts. The starter shop replaced the solenoid. I initially did try to jump the solenoid, SPARKS, but no starter spin. That test prompted the repair shop trip.

I am stumped. Not load testing was an oversight I am testing when the starter is reinstalled. Boat yoga, oh joy.

Any other suggestions are more than welcome.

[skipperpete]

There are a couple of possibilities but first off, do you have the usual Lehman relay ( piggyback relay) prior to the starter motor solenoid, they fail occasionally and cause more or less the problem you’re having. Also, try manually rotating the engine a little by hand, (your Ford originally has a slotted front pulley to enable this )…. Sometimes that click is just a failure of the teeth to mesh and moving the flywheel a bit enables engagement. Finally there’s the possibility of a dead segment on the commutator or a weakness in the armature, these are intermittent failure points that are usually revealed by doing a test on a “growler” or with a continuity tester. I’m opting for the piggyback solenoid, and if it no longer has one it might be wise to install one to eliminate the voltage drop between the keyswitch and the starter solenoid. I think it’s a Cole Hersee product that looks like a little cylinder with a few terminals

[Iron E]

After you get to what others have said about checking for a faulty the selenoid, you can check the following:
Batteries may have one or more dead cells that cause large voltage drop under engine load
The starter motor may be bad, which causes the starter to fail under engine load.

In the old days, if all was good, we would sometimes need to shim GM and Ford starters to get them to engage. They would click until shimmed correctly. But this doesn't seem to connect with your story that it worked fine until it didn't.

First I would check for voltage drop under load. If your 12.5+ batteries drop to 9V when attempting to start, then you have a connection or battery issue.
If you have 12+ volts being delivered and the starter still doesn't turn the motor, I would consider trying a new starter.

[Bowdrie]

Those solenoids that are mounted on the starter motor do two things.
1, when energized they first pull back on a little lever which pushes out the Bendix gear against a spring and engages it with the flywheel teeth.
2, at about the same time the teeth engage, the contacts close at the back of the solenoid and send power the starter motor.
The "click" without the starter motor spinning is usually one of two reasons.
1, the solenoid pulls the lever but not far enough to engage the teeth.
2, the teeth engage but the contacts didn't close to send power to the motor.
Of course, this assumes that enough batt power is available to actually spin the starter motor.

[NRbar]

After taking the starter out and putting it back on the engine it works. The last two times it was replaced identically with new shiny positive and ground but it started. Yippee. I am going for corrosion on the ground post on the starter and the disconnecting the ground and replacing it cleared up the corrosion on the post.

Thank you for the help.

Rob