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1985 K100RS sticking starter!

stevenm

New member
Hi all,

Went out to start my 1985 K100RS and the bike didn't catch immediately, not unusual when cold, but the starter did not disengage, kept chugging away. I turned the switch behind the starter button to off and it still was chugging. Turned the key off and it still was chugging away. Finally grabbed an allen wrench and disconnected the battery ground, which stopped it.

Is this most likely a stuck relay, which on my bike means a decent amount of work to simply get to as they are under the tank? Or is this a sprague clutch issue in the engine, or a stuck solenoid, or ??

It was pretty disconcerting. With the ignition switch turned off at least the fuel injection system was not pumping fuel.

Yeah, Happy New Year...

Steve
 
And charge or replace the battery while you are at it. K-bike starter relay contacts have been known to stick when the bike is cranked on a low battery, and the sticking relay results in the non-stop starter you experienced.

Best,
DeVern
 
I've had to buy this relay before. This is a common relay and physically and mechanically identical versions are available. Here are my notes about sources.


2. Stock part is Bosch # 0 332 002 161 which is superseded by # 0 332 002 168.
b. Bosch relay suppliers:​

3. TV/Tyco makes the same relay with their number: V23232D0001X001-EV-260.
 
Thanks for the info on suppliers for relays. And, it appears I can replace it by tilting the tank forward instead of having to depressurize, drain, and remove it.
 
Thanks for the info on suppliers for relays. And, it appears I can replace it by tilting the tank forward instead of having to depressurize, drain, and remove it.


Correct. You will need an 8mm socket to remove the retaining bolt, and for the cable attachment bolts (or a flat blade screw driver). If you are curious, you can test the old relay to see if it's opened back up as others here have said. I had a battery problem with my K75S a year ago and had two relays stick, but both opened up on their own after cooling down.
 
Wow, I had no idea this was such a common issue. Never had this on my trusty R65...

This used to happen a lot with the classic K bikes. Back when I was writing my monthly column Benchwrenching in the Owners News I would get several phone calls every spring after bikes had been parked over the winter. Sometimes I could hear the starter sluggishly trying to crank in the background over the phone. It happened so often that when I wasn't home and the caller said the word starter Voni would tell them it was a stuck relay and to disconnect the ground from the side of the transmission. And to then call back later.
 
Which begs the question: do you need to periodically replace the relay? My 95 has never had its relay replaced (but I always keep my battery charge since I’m aware of this problem).
 
Which begs the question: do you need to periodically replace the relay? My 95 has never had its relay replaced (but I always keep my battery charge since I’m aware of this problem).

Nope. Just keep the battery charged and stop cranking if it cranks slow. A proper running K should start within a second or two. To continue cranking just runs the risk.


:dance:dance:dance
 
I think it also may have something to do with heat. With a fully charged battery and a new relay, bike started up just fine. Went for a ride, shut off the bike. No problem. An hour later took the bike out again, started right up, stopped bike. After 10 minutes went to start again and the starter motor stuck on again, turned off key, still chugging away. Turned key back on, bike started, but I don't know if the starter was still energized. Rode bike home, turned off key, still chugging, disconnected battery ground strap. Measured battery- 13.16 volts. Let the bike cool off for several hours. Touched battery ground to case, nothing. Connected battery ground, bike started right up, and shut off properly.

Will the updated relay, with the microprocessor circuit to prevent starter from sticking, bolt into my 1985 K100RS without modification?

Thanks
Steve
 
I ran this by a friend of mine who designs high end electronic systems for racing cars (like 5,000 hp nitro dragster engines) and he immediately determined it is due to the relay being too small for the job. He designed a dual relay system, with the smaller relay triggering the larger one, so in the event the battery isn't strong enough the bike just won't start. Installed it today, in the original relay box, and it works.
 

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Not sure if there are anything specific to the relays in our old K bikes, like one way diodes and such, but I'm wondering why just installing a larger auto relay wouldn't work. I'm sure after all this time, somebody must have tried it.
 
I ran this by a friend of mine who designs high end electronic systems for racing cars (like 5,000 hp nitro dragster engines) and he immediately determined it is due to the relay being too small for the job. He designed a dual relay system, with the smaller relay triggering the larger one, so in the event the battery isn't strong enough the bike just won't start. Installed it today, in the original relay box, and it works.

I'm no automotive electronics expert, so maybe these are the proverbial stupid questions, but here I go. :) The failure is that the high current points faces in the stock relay arc and stick when there is not enough current to fully engage them and they bounce causing the arcing. I can see how this double relay setup would save the original relay from damage, but doesn't this setup just transfer the problem to the larger relay? Being a bigger relay requiring a stronger current to engage, wouldn't the arcing just happen sooner (i.e. with a bit stronger but not strong enough battery)?

Secondly, where did you find room to mount the second relay? :dunno If this works I would do it to both of my K75's and my K1200RS.

I know that BMW finally supposedly fixed this problem in the last few years of the K1200 series. I believe starting in 2003, but would have to confirm, and I don't know what it was that they did.
 
BMW addressed this by using a new relay with a built in circuit to prevent the problem. Unfortunately it isn't a plug and play solution. Apparently the smaller relay, if there is a low battery, will not have enough current to trip the larger relay, so there is no possibility of it sticking in the on position. I fit the two relays in the original relay compartment. Took a little finesse but it works fine.
 
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