Won't stop Cranking

[jimmyrich]

MF 175. Perkins Gas. 1969 model
So I go to start the tractor and it cranks a little sluggish. Turn the switch off and go to crank again still sluggish but when i turn off the key - it keeps cranking. Had to disconnect the battery to get it to stop. By the time I got that done the solenoid was smoking.
Background. Battery and starter solenoid new this summer. This happened once before - earlier this summer so I assumed a bad starter switch and replaced it. No problems - until now.
All help diagnosin gthis is appreciated.

Jim

 

[Jim.ME]

Starter may be bad, pulling the battery down, causing the solenoid to hang. Use a voltmeter and see what the voltage is at the battery cable terminal of the solenoid before cranking. Then see what it drops to when cranking. There will be more checks but that is a start.

Generator or alternator? Are you sure it is charging?

 

[jimmyrich]

Well the brand new gage I installed says its charging.
Alternator I believe.

 

[used red MN]

when i turn off the key - it keeps cranking.

If it is a Delco starter very likely what has happened is that the lock ring that retains the starter drive on the end of the armature has broke or come out of place. Due to the twisted spline that marries the drive to the armature shaft when engaged the drive tries to twist off the end of the shaft. Normally the retainer holds it from going to far. When the retainer breaks it lets the drive screw off the armature farther than normal then it’s mechanical connection to the solenoid through a fork mechanism forces the solenoid contacts to remain closed continuing to crank the engine. It could have broke sometime back, but as long as the tractor starts the drive will return and the solenoid contacts release and the starter stops as normal. Pulling the starter is the only way to confirm this has happened. If it has a brand of starter other than Delco I am not sure if this would apply.