Bizarre Intermittent Starter Issue

[crouthier]

Hi, My '72 R75/5 starter will fire off while the bike is running.

That's the headline. I had this issue a few years ago and thought I solved this with replacing the relay (a few times), but it has come back...and now I'm stumped.

Here's what's up.
- The bike runs fantastic, I just got back from a 1900 mile ride around NE.
- This happens mostly during a long ride and bike is good and warm and the engine is at IDLE.
- It sounds like the starter engages for a nano second to 1 or 2 seconds.
- The bike runs perfectly when this is happening -if it's just a second, the slightly longer bursts seems to effect the bike a bit, but then it's gone
- It's so random and intermittent, I can't make it happen again to diagnose.
- I've traced the wires looking for pinches, I replaced the starter relay, I've cleaned the starter and did a visual inspection, I've cleaned the switch (it's original) and didn't see anything wrong with it. It starts the bike and the turn signals work fine and the lock out works (when pressed - the starter will not engage while the bike is running).

I'm at a loss here. Could the starter have an internal short? Did I miss a grounding wire somewhere? Could something else more serious be making this clanking/grinding sound? It sounds like it's coming from the front of the engine...
Any one experience this before?

thank you, Chuck

 

[stevenrankin]

Front of the engine?

Are you sure it is the starter causing the problem or noise? Is it only a noise? To be honest, I have never had the starter engage when my bikes are running so I wouldn't know what would happen if it did.

How old is the bike? Could it be the timing chain? A bike with a lot of miles on it very likely could have a worn chain. I know my bikes clanked pretty good when the chains went. Every bike is different so I am just suggesting it.

Intermittent problems are a real bear to find because they only happen when you are not expecting them and not as you say when you are in the garage. So far, you have done exactly what I would do in tracking the problem down.

Good luck, St.

 

[crouthier]

thanks for the thoughts. I have no idea if it's the timing chain and not sure what a worn timing chain sounds like. The bike only has 36,xxx miles - so it's not high miles. It's like a quick rattle/clatter and then goes away - it's there one second then gone, and to me, sounds like the starter trying to engage...what's puzzling is that the bike doesn't respond to the 'noise' usually - meaning it just idles away, nice and solid. However, today it did seem to 'react' when the noise was longer than 1 second...c

 

[20774]

Every time I hear of /5 starter issues I think of the "cricket" issue. Snowbum talks about this issue and the modification is needed:

https://bmwmotorcycletech.info/slash5cricket.htm

Also, I think there is a diode in the headlight shell which can fail that might create the situation posted about here. Not sure of the exact details.

 

[crouthier]

Thanks Kurt, I did give that a read last time I was trying to solve this issue. It sounds like the /5 starter relay is not great to begin with. I may try the 'fix' as I have my original.

Because this issue shows only at low rpm (I believe the relay works at higher RPM only) I suspect that the relay MAY be working as designed - but a short somewhere (the starter switch?) is firing the starter from time to time but only presents at low idle...It's driving me nuts though as the bike is running so great otherwise.

thank you for your help.

best Chuck

 

[nickrides]

Chuck
I kinda have my doubts its your starter engaging.
But, that said, a starter engaging on a running engine is a unique and easily recognizable sound. We've all turned the key on a running engine by mistake.
Is there a easy way for you to disconnect it once the bike is running and warmed up?
I know its not the safest thing to be running around without a starter in case you kill it in traffic, but you could take this variable out of the equation.
Ride safe in 2020
Nick

 

[stevenrankin]

36k

At you mileage, I would not expect a timing chain to be bad. I won't say it can't happen but I doubt it.

That leaves a lot of other areas open for the search.

I don't know if you could pull the stater wire off of the stater relay once the bike is running to kill the starter as suggested. I know to pull the connection off of the starter itself is a pain to get at as it is under the one engine cover.

Man, I feel for you, I loathe intermittent problems, There is nothing as frustrating than having a customer bring a vehicle in saying it is doing this.,,, and for me it wouldn't. Sadly, we don't have x ray eyes and sometimes have to take things apart to find the problem.

Sorry I can't help more, If you are near Rochester, or Buffalo, perhaps we could tackle it together. St.

 

[crouthier]

Hi Nick and St. Thanks for the thoughts. It's soooo intermittent that it took me by surprise. Yes, I was going to pull over and unplug the starter, but it happened only twice on this trip, and I was close to home. So I thought i'd try to make it happen when I got back with some wire manipulation or switch fiddling. I did try moving wires where it made sense but could not trigger the starter...

I know, it's hard to believe that the starter is engaging, it doesn't make sense. And I am pretty sure that's what's happening, but of course could be something else. Could a timing chain tensioner somehow come loose? Or the spring? I bet I'd hear some chain slap, or something like that and I don't, the engine sounds tight. And if that were the case I am sure i'd hear it at all revs, not just at idle (unless I just can't hear, but it's pretty loud).

I do think my switch is not 100%...and I know they are not avail any more (to eliminate). But I'd really like some physical proof of what's going on so it's not guess work, until it happens again next time!
C

 

[20774]

If you suspected the timing chain or tensioner, I would think that bits and pieces would end up in the oil filter. You could stretch out the pleats of the filter the next time to look for telltale signs.

 

[stevenrankin]

Not 100%

Well, I switch could be the problem. It may be engaging the starter when you don't want it too.

Not to be a smart ass but might you perhaps bumped the stater switch by accident a couple of times? With jackets gloves and such, we don't have tactile feeling and such.

Also, You have inspected everything only to find nothing out of sorts, My suggestion is to ride. If something is failing, it will act up more and more or, it will fail completely. Either way, it makes it a heck of a lot easier to find and fix.

Yeah, I know it bugs us to have something going on. I spent two years chasing down an intermittent cut out problem. Started out minor, got worse, checked rechecked, re re checked, cleaned switches, contacts, NEVER did find out the source of the problem. It just disappeared one time after the fifth check of the grounds. While I was riding and the problem would turn up, I made sure I belonged to the MOA road side assistance program. Never had to use it for that problem but did have to use it once and it was worth the money.

Sorry, I can't put my finger on your problem, keep us up to date on your progress, maybe a light will come on and someone will figure out the problem. Cheers, St.

 

[stevenrankin]

Vintage BMW

Mac Kirkpatrick of the Vintage BMW club reported in the Classics forum reproduction /5 switches are now becoming available.
/5 repro handlebar switches are now available from most suppliers of vintage BMW parts such as:

Bob's BMW
Ulis
Vintagebmwparts
Salis
Moto Bins
Motoren Israel
Bench Mark Works
Max BMW

St.

 

[pglaves]

I would venture the following: If the starter motor is spinning while the engine is running it is doubtful that the starter nose gear is actually engaging the ring gear. If engagement actually happens what usually happens is that the engine spins the starter armature so fast that the centrifugal force causes wires to break and other unfortunate things.

 

[crouthier]

Thanks Paul and St. Of course I always go to pilot error first, but for sure I didn't hit the starter the last few times - I was sitting at a stoplight. And actually, the lock out works, I did hit the starter intentionally to see if it was operating properly and it worked at designed, the starter did not engage...

I'll do more investigating and yes, a good option is to keep going until it gets so bad it may be clear what the issue is. Thanks for the heads up on that switch being avail. It looks like Max says it's still not avail, but Bench Mark Works has the button, but not the wiring? I'll give them a call.

I'll keep you posted.

regards, Chuck

 

[stevenrankin]

switch

the Switch available now may not be direct from BMW. There are some companies making parts available at their own sites. Max is pretty good with keeping up on the latest news and available parts, at least for BMW listed parts. St.

 

[crouthier]

minor update

I've been talking to EME where I got my new starter relay. These relays do work with alternator and battery, if the battery is compromised at low revs the lock out feature will not work. I tested this and indeed my starter engages with the bike running at my normal idle. So my theory is either the switch or the Bosch starter has a short, a very intermittent short.

I'm going to load test the battery first. Then pull the starter and investigate. It's harder to diagnose the switch, but I will trace the wiring to confirm it's not a pinched or bare wire somewhere, and I guess, get a new switch when they become avail (Matt at EME says they will get soon).

Will keep plugging away.
C

 

[stevenrankin]

Switch

Hey, to be honest, I would go with working the switch a few more times before I went to the trouble of buying and replacing a starter.

I am not familiar with the internals of your switch but perhaps the spring is shot and it is letting the contacts touch internal. Or there is a piece of something causing a short internal. Or perhaps just plain gunk and corrosion are bridging the contacts internal.

I imagine you have sprayed as best you can the insides of the switch with an contact or electrical cleaner first. Maybe, it is possible to carefully take the switch apart to see what it looks like internally. I do know if you choose this route, be very careful not to force things and look out for very small parts to come out.

Of course, taking the switch apart may NOT be an option, as I say, I don't know about your switch and how it is assembled.

I would also check in the headlight shell, a crowded place at the best of times. There may be something going on in there where a wire is off or touching or something. I once had a Fues blow and the tin from it dropped inside the headlight shell and shorted out the turn signals causing an intermittent blink and of course more shorts and blown fuses. I went nuts before I found the problem.

I am not saying there may not be a problem with the starter, there very well could be. I am just one of those people who expend every effort checking and rechecking before replacing. Hanging around my friend's shop as well as working on many vehicles of all types over the years, a lot of the time the problem is the simple fix. The pain is the Intermittent part of it. So much nicer to have something fail and be done with it. Good luck. St.

 

[crouthier]

Hi St. yes, good advice. I did manage to take apart my left hand switch. It is tricky but do-able. I will try that first and I did spray the starter switch with brake cleaner - didn't do much. I will also look in the headlight bucket as well...it is totally jammed in there...

And, yes, it is way easier to get to the switch first, then the starter later, and I have all winter coming up to fiddle, a project!...thanks for response.

Chuck

 

[stevenrankin]

Winter

Yep winter, I have my main ride already torn down to the bare frame as I have been grounded from riding for a bit and winter is coming. I still have another bike to ride. St.