Non stop starter

[r75bitsa]

Have done all of the oils, all dash lights and indicators,stop lights etc work, time to wind her over to get the oil through. Clutch in press the button, turns over no problems, thumb off the button she's still going. Funny how you stand there for a few seconds thinking wtf, then the scramble for a Phillips head. The motor is a 78 r100 with the wiring loom of the period and switch gear,it has the starter to match and up to this point there has been no problems getting everything to work. The battery had just had a full charge to top it up. Of course you have to do it one more time to convince yourself, yes it really did happen. Would this be a relay problem,as it is the proper BMW jobbie, or would it be a solenoid issue. All of the wiring loom engine and headlight assy are in a 75/5 LWB.

[jagarra]

I had a solenoid stick once, had to pull the battery cable to get it to stop. I would pull the starter and take the solenoid apart, bet the contacts are pitted may be sticking. Also check for freedom of movement on the plunger on the solenoid, in fact check everything for freedom of movement.

[ME 109]

Check the start button, it may be sticking or broken?

[r75bitsa]

Just got back from a cup pissup, didn't mention the bike hasn't been running yet. I was in the process of checking whether it would turn over, so remoting to the solenoid to exclude the switch probably won't count. I have checked the switch as far as looking at the plastic back but haven't gone any further, will probably damage something else will wait till tomorrow.
Regards to everyone.

[SteveD]

Just got back from a cup pissup... will probably damage something else will wait till tomorrow.
Regards to everyone.

Wise

[Bamboo812]

You can eliminate the starter switch and relay from the test by shorting across the two black wires going to the solenoid with a screwdriver. You'll need to remove the starter cover to accomplish this. Just disconnect the ground cable and hold it to ground for a quick disconnect in case it's the starter that's sticking.

[r75bitsa]

Disconnected the black wire, wire from battery positive to the terminal, turned over, pulled the power and it stopped. Is that a sticking or stuffed switch, sorry to the blokes that suggested that earlier, this is new ground for me who is used to a steady feed of ujm's

[jagarra]

I think you may be testing it incorrectly. I have never looked at the solenoid on a BMW, but here is what you should be doing. If the solenoid has three terminals on it, 2 of them are really heavy with one of them hooked to the battery those are the two that you should be shorting out. What you are trying to do is short those 2 heavy terminals together, this will allow power from the battery to go to the starter and it will spin. If you remove your short(the wrench or screwdriver) and it is still spinning the fault is the solenoid sticking. If the starter stops when the screwdriver (short is removed) then the problem is further up the line, either the relay or starter button. We have you loosen the ground from the battery as a safety feature which will allow you to stop the whole operation if the solenoid is indeed stuck.

Now if the solenoid has only 2 terminals, one heavy and one lighter, shorting those will accomplish the same result.

[Duane Ausherman]

This article might be of some help. http://www.w6rec.com/duane/bmw/starter/index.htm

[Snakeoil]

If the solenoid has three terminals on it, 2 of them are really heavy with one of them hooked to the battery those are the two that you should be shorting out. What you are trying to do is short those 2 heavy terminals together, this will allow power from the battery to go to the starter and it will spin. If you remove your short(the wrench or screwdriver) and it is still spinning the fault is the solenoid sticking.

Sorry and no offense intended, but that is not a correct statement. If you short the two heavy terminals on the solenoid, you are in essence, bypassing the solenoid. I cannot see how a starter itself could stick and remain running. So, all you are doing with this test is confirming that the starter works. You've taken the solenoid out of the circuit.

I must plead ignorance on the physical layout of the starter and solenoid. Wiring diagram indicates that the solenoid is attached to the starter physcially. So I'm not sure if you can get easily to both of starter side power wires on the solenoid. If that is the case, then it might be easier to remove the feed cable from the battery to the starter and use the sound of the solenoid clicking open and closed to do any testing. Cranking the starter motor over and over could overheat it.

What you need to do is jumper the other side of the solenoid with a power feed. This is the wiring coming from the relay that energizes the solenoid. This will bypass the relay and starter switch and cause the solenoid to operate, which will close the contacts and energize the starter if still connected to the solenoid. If you remove your jumper and it keeps running or if you disconnected the starter, and the solenoid clicks closed, but does not click open when you remove the jumper, then the solenoid is sticking. If the solenoid clicks open when you pull the main battery cable, that confirms that the solenoid itself is sticking or for some reason, is electrically sealing shut (see explanation below on electrically sealing shut).

If you prove that the solenoid is not sticking, for subsequent functional testing, you can disconnect the starter motor and put a DMM across the starter motor terminals on the solenoid and watch the solenoid function that way. Or simply continue to use the clicking as an indicator of function. A solenoid is nothing more than a magnetic switch.

I mentioned electrically sealing shut. You may find with further testing that the push button and the relay are both fine. I say this because I went down this road once with a Harley rebuild. The factory wiring diagram actually had an error that would seal in the solenoid once it was energized. I knew it was a mistake, probably stared at it for a half hour trying to figure out how it could work correctly that way. But I was young and believed all manuals were perfect if from the factory. I wired it that way and needless to say, first push of the starter and the motor cranked endlessly until I pulled the battery cable. So, my point is, you may have a wiring error that seals in either the relay or the solenoid as soon as it is energized. Given this sounds like a Frankenstein bike, the potential for this type of error exists. So, if everything appears to be functioning properly, you need to look for a wiring error that will cause this.

I hope this was helpful.

regards,
Rob