Starter staying engaged

Have a problem on an AC175 Diesel. The starter stays engaged. I took it to a repair shop and the solenoid was replaced. The mechanic said in cold weather this will happen if voltage is low. I made sure battery was recharged. The starter button did not engage starter so I bypassed and again the starter stayed engaged. Can anyone tell me why this is happening?

Check your wiring/ground connections.

Bad wiring can draw more current which obviously has to run through the solenoid too.

When too much current has to run through - the contacts can kind of weld together.

Usually a sharp smack with a screw driver handle or something against the solenoid will free them if it's something that only happens very occasionally.

Meanwhile - next time it happens, first stop it, then feel your wires - willing to bet you'll hit one that's red hot. (be careful - I do mean RED hot)

Low voltage causes the solenoid to get hot which in turn causes the contacts to weld up. One needs to remember that a battery can be full charged but if a cable or connection is bad volts also drops to the point it causes that to happen

Try another solenoid, you may have one bad from the box, an "Out fo box failure", or may have some buildup on the starter shaft holding the starter bendix into the flywheel at the same time the plunger inside of the solenoid is pulled down and making contact across the leads, keeping the starter motor engaged.

I am not familiar with the AC 175, but the mechanics of a starter motor, bendix, and solenoid are pretty much universal, depending on where the solenoid resides.

Also, take a look at the bendix without power being delivered to it. Is it recessed back into the starter motor when idle as is supposed to be? Or, is it engaged into the flywheel when idle where is NOT supposed to be? If you bypass the solenoid, disconnect it, and it the post on the starter where the solenoid would connect, the starter motor SHOULD engage, the bendix SHOULD move into the flywheel, and as soon as you remove the voltage, the spring loaded bendix should disengage from the flywheel.

When you say "The starter stays engaged", its possible from that description that you just have a bad bendix or spring that is not disengaging, thus keeping the starter motor spinning because the flywheel is continuing to drive it through the engaged bendix. Try warming up the starter with a heat gun or heater, you may have it iced up especially if you leave it open due to not having an inspection cover to protect it. Been there, done that.

Mark

I've had that happen on my 1755. I had also been having problems with it turning over slowly when hot. Turned out to be a bad crimp on my ground cable, where it attached to the frame. As previously mentioned, I would check all of your connections closely
Good luck

Also make sure the thrust washer and snap ring collar are both in place. If broken and missing the drive will travel too far. Had the same trouble with a Delco on MF 265, found both parts broken. Was found after a new solenoid was installed and had the same trouble.

If it's like my AC, there is no Bendix drive. My AC has a Delco starter with an over-running clutch type drive.

Load test your battery and clean all connections. I had this happen (starter stays engaged even with switch off) on my Perkins and almost started the tractor on fire since the engine failed to start and it kept cranking. I took the starter off, but could find nothing wrong. Put it back in with different battery and it works fine, so I know that no contacts were welded together.

Delco 27MT starter I assume. You need to ascertain if the plunger inside the solenoid is sticking . . . or if the contacts in the solenoid cap are pitted and sticking . . . or if the voltage going to the solenoid "S" terminal isn't being cut off. When you turn the key and power gets to the "S" terminal - an electromagnet pulls a metal plunger against a spring that pushes against a rocker-arm that puts the starter drive into the proper place. Once pushed all the way a button is pushed in that makes the copper contacts close and make the armature spin. The starter drive has no "Bendix." It uses a sprag roller clutch that acts like a one-way rachet. As another poster mentioned - if the starter drive gets stuck "engaged" - it prevents a sort of "back-feed" and keeps the power going even if the power is shut off to the solenoid. Delco direct-drive starters have a pretty weak drive-stop at the end of the armature that come off at times. So - your problem can be stuck contacts, sticking plunger, broken drive stop, etc.

Replace or rebuild. It your starter is wornout. They only last so long and when they start giving trouble it's time to replace them. Will save you a lot of time and money to do it now or wait and play with all the so called cures it will wind up costing a lot more in time and money.
Walt