Possessed starter motor

I just installed a new 'Dyno Dave' high output starter motor (75 Mk3). Last night I started the bike both with the starter and kicking it over about a dozen times. Everything seemed in perfect order... until this morning. I kicked it over once (perfect) and shut it down, tried the starter and things went haywire. The starter kept spinning, and spinning. I hit the kill switch, still spinning... I turned off the key, still spinning... the starter kept spinning until it drained the battery. Ok, wiring wrong somewhere, but why didn't this happen yesterday? Sometime overnight the bike became possessed? Anyone ever have an out-of-control starter motor?
-paul

Well now I KNOW I screwed up somewhere... just pulled the battery but could hardly hold onto it because it was so hot. Probably ruined the battery. Lovely.

I think you will find that it is the solenoid "sticking" and not returning to the static position. I had this with my Commando when I first installed an electric starter, but after replacing the solenoid, I have not had it recur again.

It is alarming though when it just keeps turning the engine over :?

Yep , had the exact same problem once . Solenoid was the culprit .

The factory should have used nice, reliable LUCAS solenoids-instead of Prestolite! :mrgreen:

I just replaced the solenoid! A friend and I were going through the electrics and there seemed to be grounding problems. The old solenoid had a ground wire leading from the left-hand nut to the positive battery terminal. I replaced this with a ground wire to a frame bolt. We had checked to make sure we had continuity from the positive battery terminal to this frame bolt, and we did. If somehow the solenoid became ungrounded, it would simply not operate, right? So that the solenoid stuck closed means that it's bad. My question is: what would cause a solenoid to fail? It was new, so it's failure may be a symptom of a larger problem which I need to fix. Thanks in advance.
-paul

Why L.A.B., I do believe you are becoming a cynic.

c.cito said:

My question is: what would cause a solenoid to fail? It was new,

Click to expand...

"New" doesn't mean it can't be faulty?

c.cito said:

so it's failure may be a symptom of a larger problem which I need to fix.

Click to expand...

That's unlikely, I think, as solenoids generally stick "ON" when the heavy amp contacts do not make proper..er.."contact" with each other, which causes arcing that can generate enough heat for them to weld together!

The problem could have been caused by a bad connection (that the meter didn't show) not necessarily on the ground side, so the solenoid may not have been operating properly, or it can also be caused by low voltage (although probably not in this instance).

The solenoid return is indeed through its case. However, in spite of the factory wiring, you should not depend on a connection to the frame as anything but a redundant ground, and run a dedicated return wire to the positive battery terminal, assuming your bike is positive ground. The exiting current is small, and any wire gauge will do.

The solenoid is designed to make and break under full load, so if the contacts are fused (remove all connections to the solenoid to check), and the solenoid is new, send it back. There is an outside chance that the exiter coil "hot" tab was permanently driven to -12v via a wiring problem, and the solenoid exceeded its maximum duty cycle during its "runaway" experience, fusing the contacts. Did you turn off the ignition switch during this experience, or rely on the kill switch? Operating the kill switch interrupts the ignition current but does not interrupt the exiting voltage to the solenoid, which relies on "switched" power (white wire) through the ignition switch and through the momentary starter contact. Is the starter button contact fused?

I don't have electric start on by bike. But I would check everything over. Lead acid battery level. Engine start switch. Polarity. Make sure the starter isn't still stuck on. I also have a disconnect on my battery so I can disconnect it quickly as removing it quickly, physically is hard. Disconnects need to be rated for the current they break so because I dont have a starter my current is fairly low. you would need a bigger disconnect. Remember if you use a disconnect designed for Alternating Current you need to go twice as big for use on Direct Current due to the nature of DC.


I would say the solenoid failed, which causes the starter to keep running and because once the starter is running the only thing that stops it is the spring in the starter, you can turn off all the switchs in the world but unless you disconnect the battery it will keep running. Once the battery voltage is low enough it doesn't spin. Keep in mind that it doesn't mean that current isn't still flowing through the windings on the starter it could be drawing power but not spinning. Not only that as voltage decreases current will increase so you could have a very large amount of current going through the windings. This could burn out the windings (burn open the windings). Not trying to be negitive. HAHA (polarity ...being negitive...ya....) anyway.

So but as to why it happened the next day. Restarting you bike a whole bunch of times with a starter is not a good idea. It heats up the contacts in the starter which changes the molecular substance and makes them soft, and any weaker spot on the contacts will make a hole in the contact and cause a failure. This could either be a fail in contacts welding together or burning open.

My 2 cents.

$17 later and the bike appears to be running. I replaced the solenoid, ran a check on the wiring, put in another battery, and she fired right up on both the starter and kicker. One thing I noticed is that the fused lead off the negative looked dicey, so I gave that some attention as well. I'll take the old solenoid back, but I am half tempted to tear into it and see what happened. I try not to use the starter too much, but it is nice to have... Thanks for the help, now maybe the bike and I can get reacquainted.
-paul