BMW K bikes (Bricks)


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SunnyPerth

SunnyPerth
Silver member
Silver member
Hi team, 

This time something different 89 K100 RS. Normally rides fine. Short or long distances, dry or wet weather. 
However I now had it twice that I lost the tachometer and lost power (running rough on only 2 cylinders). 
Both times this was just (minutes) after I left home with a cold engine. Given one time it was raining but this evening it was dry and cool outside.    Trying to keep the bike running, turned around, played around with the throttle, and then after a few min, it all started working as normal again.  

All clearly indicates either a failing coil or hall sensor, or potentially a loose wire/bad connection. 
While I have checked the coils before (they are ok) I have not tested the hall sensor yet. 
Will do that using this  "BertVogelK100TroubleShootingStarting.pdf" description with the Led, but my fear is that this won't tell me anything as the bike normally runs fine. (including when I parked it again).  As this only happened twice (over a 6month period), with a (reasonable) cool engine (so don't think it's heat related), I do think the more likely cause is either a loose wire. 

Where would we start? Any suggestions or learnings what connections to check first? 
- hall sensor plug to main loom
- ignition module 
- earth cables
- Tacho pickup at coil (is that a separate cable?) (need to check)
- ECU (albeit I cleaned that before, and all seems to be ok) 

Ideally I want to run the bike and then test all the connections (wiggle them around) to see if I can reproduce. But where to start? 

Any ideas?   or does anyone want to place a bet on what it is? 

Cheers,
y.

    

2Back to top Go down   Hall sensors, Coil or just a loose/bad connection?  Empty Hall sensors or other stuff Tue Oct 31, 2023 5:45 am

daveyson

daveyson
Life time member
Life time member
Hi Sunny,

I'll place a $1 bet on a guess. I think your thinking is good. I'd swap the coils. If the problem returns but the tacho is good, that makes the coil look bad. If the tacho is still bad, one of the other parts you mentioned is not looking good.


__________________________________________________
11/1985 BMW K100RT (late model)  Vin. 0090567
 ~120,000 km
    

92KK 84WW Olaf

avatar
Life time member
Life time member
If you are also losing the rev counter like that my money is on the 2/3 coil defective as it also feeds the rev counter.

But it does not preclude the Hall sensor for 2/3 being bad. So swap the coils as recommended. If the problem transfers to 1/4 then its coil. If the problem remains at 2/3 then Hall sensor or wiring/connectors from it becomes prime suspect.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011157 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 58,200 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 51,800 miles.
1983 K100RS 0004449 Odette R100 colours 58,000 miles. Sprint fairing now 63,390 miles

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

4Back to top Go down   Hall sensors, Coil or just a loose/bad connection?  Empty Hall sensors or Tue Oct 31, 2023 7:25 am

daveyson

daveyson
Life time member
Life time member
True but looking at the drawings makes me think it's the coil for cylinder's 1/4 that controls the tacho. So if the problem is the coil, the tacho problem won't transfer by swapping the coils, it will disappear, is what I'm thinking.


__________________________________________________
11/1985 BMW K100RT (late model)  Vin. 0090567
 ~120,000 km
    

SunnyPerth

SunnyPerth
Silver member
Silver member
Great suggestion guys. As this happens so randomly and incidentally, I don’t want to do to many changes at the same time. Sound thinking. If it happens again, and rev counter dies, then it’s likely not the coil. Also this is the easiest thing to do, as it means I do not need to trace the hall sensor wire to the plug, to be able to test. which I assume sits under the tank.

you guys talk as if you hear (or see) from the engine if cyl 2&3 or 1&4 fail? Or is there another trick besides pulling spark plugs to find out what cylinder (and coil) are not firing?
(as this happens on the road, and so randomly) and the engine dies if I do not keep reving it by hand, removing spark plug cover and pull plugs isn’t really handy or quick)

(Got to love these challenges with old bikes !)

    

6Back to top Go down   Hall sensors, Coil or just a loose/bad connection?  Empty Hall sensor or Tue Oct 31, 2023 8:58 am

daveyson

daveyson
Life time member
Life time member
A timing gun clamp around spark plug 1 lead, for example, is a quick way to see if it's getting spark.


__________________________________________________
11/1985 BMW K100RT (late model)  Vin. 0090567
 ~120,000 km
    

92KK 84WW Olaf

avatar
Life time member
Life time member
daveyson wrote:True but looking at the drawings makes me think it's the coil for cylinder's 1/4 that controls the tacho. So if the problem is the coil, the tacho problem won't transfer by swapping the coils, it will disappear, is what I'm thinking.

Thats good thinking and at no cost.

Don't dismiss the idea of a bad plug, HT lead or plug bobbins!!


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011157 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 58,200 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 51,800 miles.
1983 K100RS 0004449 Odette R100 colours 58,000 miles. Sprint fairing now 63,390 miles

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

SunnyPerth

SunnyPerth
Silver member
Silver member
daveyson wrote:A timing gun clamp around spark plug 1 lead, for example, is a quick way to see if it's getting spark.
Very true, but… I don’t usually carry that with me on the road. And this only happens very very occasionally 🤣. Will put in some tools that allow me to pull leads when this happens again.

    

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