B8200 starter circuit schematic

[CTWright]

I'm working on a B8200 for friend. Would not start. The starter was shot, like it got jammed in the flywheel and "cooked" it. He got me a new starter so I bench tested first successfully. Once installed it wont start from the key switch. Tried jumping the solenoid and it engages and turns over the engine, but won't stop without disconnecting the battery. So he solenoid stays engaged and keeps cranking. Anybody have a schematic of the start circuit so I can troubleshoot this?

 

[100 td]

Besides the schematic, if you are jumping the solenoid and it continues to crank I expect the ring gear could be damaged and is not allowing the bendix to disengage.

BUT I would check one important thing first, the connections on the solenoid.
Are there 2 separate connections on the solenoid?
It may be possible you have the wiring connections around the wrong way on the solenoid and when you jump the starter, the supply through the stop solenoid circuit is enough to energize the "hold in" coil and keep the solenoid engaged. Hence the continued cranking of the starter. The electrical circuit will be similar to most of these machines, interlocks will be clutch switch, PTO switch, and HST/Neutral switch.

 

[CTWright]

Only the lead from the battery, a power wire back from that post and one spade connection for the solenoid engagement. If I pull the spade connection after it starts turning there is still voltage at the connection. I'm thinking bad solenoid. Despite it bench testing OK.

 

[100 td]

A tad tricky but.......When the solenoid is in the "closed state", which is after energization, and it has pulled in, and closed the main contacts, both main contacts now have positive power on them. Attached to the main contact terminal is the motor stator and armature circuit, (so the motor spins as it's circuit goes to ground) as well as the other end of the "pull in" winding of the solenoid. (So the pull in winding now has positive on both ends so no current flows)
When positive power is removed from the start terminal of the solenoid, power is now supplied "through" the pull in coil to that terminal which then supplies power to the hold in coil (to ground). However, the direction of current flow is now in opposite directions in each coil so the magnetic flux of each coil cancels each other out and the solenoid opens and breaks the circuit. (The solenoid plungeris pushed back by the spring.)
So why is the starter staying engaged?
If all wiring is correct and the starter bench tests OK,
Damaged teeth on the ring gear, unlubricated bendix or solenoid sticking under load?
How strong is the solenoid return spring?
Has anyone repaired the solenoid an connected the coils in the wrong direction?

 

[Weaselfoot]

Sounds like the hold circuit of the solenoid is still engaged. The ignition switch is still in the start position. My guess is that the ignition switch is faulty.

 

[100 td]

If I pull the spade connection after it starts turning there is still voltage at the connection. I'm thinking bad solenoid. Despite it bench testing OK.

I read this to mean there was voltage at the starter terminal after removing the connection. If there is still voltage measured on the wire then the start relay/switch would be a likely cause. However he stated it wont start from the key switch. Diagnosing from afar without doing the testing oneself is fraught with problems!

 

[Weaselfoot]

Very true about diagnosing from afar! But I think we are getting close. The pull in windings require a lot more current than the hold in windings to operate. Is it possible the ignition switch is not conducting enough current to activate the pull in? When the solenoid is jumpered then the solenoid pulls in with the added current. Once in, the solenoid makes the contacts and the engine rotates. The faulty switch is still providing power to the hold circuit (the pull circuit is no longer needed -it is off as 100 td stated) and the solenoid stays engaged and the starter stays engaged in the ring gear. CtWright, please try this: turn the ignition key to ON (not START) and then jump the starter. If we are on the right track, then the engine should start and the starter should disengage. I am assuming here that the spring return in the switch is faulty. At any rate it appears that two things may be happening at the ignition switch: corrosion etc. is preventing current flow across the START contacts and the START contacts are staying on after the engine starts. Dirt and a broken spring in the switch?

 

[Weaselfoot]

Fixed?

 

[CTWright]

Tried the ignition switch on and jumping it. Still kept turning until the battery was disconnected. It's out of my hands now. The owner is taking to a shop for additional work.

 

[Weaselfoot]

Thanks for replying and also for posting the problem in the first place.