Coil might be bad

[FlatSix]

Gents,

Went for a ride with the wife (a month ago before it got blazing hot) and it was barely running.  Quick turnaround (wife not pleased) and parked the brick.  Last ride before that it started fine but seemed to be running rough by the time I got home.  I suppose it didn't magically fix itself. 

Removed the plastics to get a good look at things to see what's up.  You know...just the usual, hey maybe something fell off or something.  No obvious missing parts.  Bummer.  Perhaps an air leak (I visually checked but didn't get around to testing with propane) but nearly every rubber part is newish.  Pulled the plugs and they looked good.  Got out the multi-meter to make sure the coils were giving me the juice and got some unexpected readings so I pulled them off the bike to make sure I tested them properly. 

Looks like one for sure and possibly both might be bad.  Is 10.72 ohms serviceable for 2 - 3 coil or is it bad too?  It's not easy to get readings on the high voltage side but I happen to have some long probes  and I assure you they were making contact....I promise!

And what kind of junk coil fails after only 35 years?

Dave in TX

[Laitch]

Is 10.72 ohms serviceable for 2 - 3 coil or is it bad too? :

10.72Ω or 10.72kΩ?

[frankenduck]

Looks like you have first gen coils.  I'd replace both of them with a good pair of used second gen coils.

[The Mighty Gryphon]

Looks like you have first gen coils.  I'd replace both of them with a good pair of used second gen coils.

+1  The early coils had a problem with insulation breakdown.  Used 2nd generation coils are almost bulletproof.

[frankenduck]

If you're looking on Ebay or wherever for coils then it's easy to tell first gen K100 coils from second gen coils. The spark plug lead terminals are orange instead of dark gray.

[FlatSix]

10.72Ω or 10.72kΩ?

Haha!  It's the "K" version of course...my bad.

[FlatSix]

+1  The early coils had a problem with insulation breakdown.  Used 2nd generation coils are almost bulletproof.

Looks like you have first gen coils.  I'd replace both of them with a good pair of used second gen coils.

If you're looking on Ebay or wherever for coils then it's easy to tell first gen K100 coils from second gen coils. The spark plug lead terminals are orange instead of dark gray.

Duly noted sirs.  Thanks for the help.  I will be on the lookout for a set of newer second gen ones.  The "new" ones at Max are pretty pricey and not sure if they can even be had.  Yikes.

[Laitch]

For the record, here is an extract from the compelling literary work, BMW Diagnose–Testing for K Models, which tells us that one of the coils is OK— until it isn't, which essentially is a description of the general condition of humanity, too. 

[FlatSix]

For the record, here is an extract from the compelling literary work, BMW Diagnose–Testing for K Models, which tells us that one of the coils is OK— until it isn't, which essentially is a description of the general condition of humanity, too. 

Thanks Laitch that is very helpful.  The "Troubleshooting Guide" I have saved on my computer just shows the High Voltage segment of the coil should test about 12.6K ohms.  I should be able to get on the road quicker if need be with only one coil. 

I do think I am going to try and get two newer version good ones if I can find them.  My objective in rebuilding this bike was to make it as reliable as possible by replacing or upgrading any potential wear items.  The coils were one of those items that I should have just bought new when I put it together.  $$$  You live, you learn. 

[FlatSix]

Follow up:  Can the coil, part number 12131459890 be used, if the wiring can be adapted?  Looks like it uses a different plug.

[The Mighty Gryphon]

That coil is from the K1100 and works with the Motronic system.  Your bike has the Jetronic, and the ignition signals may not be the same.  I would go with a K100 coil to be sure it will work and not damage anything.

https://www.ebay.com/itm/123719811660?fits=Make%3ABMW&hash=item1cce46824c%3Ag%3AITgAAOSwtfhYrLkM&LH_ItemCondition=4

[FlatSix]

That coil is from the K1100 and works with the Motronic system.  Your bike has the Jetronic, and the ignition signals may not be the same.  I would go with a K100 coil to be sure it will work and not damage anything.

https://www.ebay.com/itm/123719811660?fits=Make%3ABMW&hash=item1cce46824c%3Ag%3AITgAAOSwtfhYrLkM&LH_ItemCondition=4

Thanks TMG, I will stay with what I know works.  The link you sent...that coil has a different plug than mine as well. 

[beemuker]

List says compatible with K100RS, not 100LT. only 1100lt. keep looking. I just got one for $50 for my R1100.

[Laitch]

List says compatible with K100RS, not 100LT. only 1100lt.

The list is referring to the 4V version of the RS, not the 2V.

[The Mighty Gryphon]

Doh!  The coil I linked is for the Motronic system.  Don't use it.  I don't know what I was thinking when I looked at the listing.

[FlatSix]

Thanks guys.  I am on the hunt.

[Duckbubbles]

I am using the stock coils on my '85 K100RS with a '93 K1100LT Motronic.  Had to modify the ignition leads to plug into the earlier coils.  I believe the difference between early and late coils is the way the trigger leads attach.  The early coils use separate blade connectors while the later coils use a two pin plug. 

Frank 

[Laitch]

I believe the difference between early and late coils is the way the trigger leads attach. .  .

Another difference is that K1100 4V coils have 0.5Ω primary resistance and ≈13.5kΩ secondary resistance, compared with ≈2.5Ω primary resistance and ≈10.5kΩ secondary resistance in the 2V coils. What you've done is used coils in your K1002V appropriate for use with the Motronic in your 2V. Using them with a Jetronic ECU might have a different result, as indicated by this observation.

I'd be careful about using coils with a lower primary resistance.  This will cause more current to be drawn through the ICU drivers, and possibly destroy the ICU (as the drivers will overheat). 

[Duckbubbles]

I did no research on the differences in the coils.  I've been using my original '85 coils on my '85 RS while running a '93 K1100LT engine, Motronic, airbox, engine harness, O2 sensor and adapted the '85 bike wiring harness to run the Motronic..  The conversion was done (by me) 19 years and 50,000 miles ago.
Picked up the engine and systems from a salvage yard and probably should have gotten the coils, too.  Wouldn't have had to replace the coil trigger plugs.

Frank

[FlatSix]

I did no research on the differences in the coils.  I've been using my original '85 coils on my '85 RS while running a '93 K1100LT engine, Motronic, airbox, engine harness, O2 sensor and adapted the '85 bike wiring harness to run the Motronic..  The conversion was done (by me) 19 years and 50,000 miles ago.
Picked up the engine and systems from a salvage yard and probably should have gotten the coils, too.  Wouldn't have had to replace the coil trigger plugs.

Frank

It is good to hear you haven't had any issues with this setup, fellow Texan. 

In looking for the newer versions of the coil I need I received disheartening news when inquiring about new ones:  "Unfortunately these coils are discontinued by BOSCH and BMW with no aftermarket option available.  We have sold the last of our inventory and will not be able to replace them."

I have not yet exhausted my search.

There must be someone smart with this electrical wizardly that can figure out how to use an alternative coil. 

Dave

 

[The Mighty Gryphon]

Just for laughs, you might want to place an order for p/n  12 13 1 459 513 from MaxBMW.  Their website doesn't show it as not available so maybe there are still some around.

It's going to be a bit pricey at $242, but there is no shipping or sales tax. 

[FlatSix]

Just for laughs, you might want to place an order for p/n  12 13 1 459 513 from MaxBMW.  Their website doesn't show it as not available so maybe there are still some around.

It's going to be a bit pricey at $242, but there is no shipping or sales tax.

I'm ahead you there TMG...waiting to hear back and hoping for good news.

[FlatSix]

I'm ahead you there TMG...waiting to hear back and hoping for good news.

No joy.  I will post in the WTB section to see if there are any out there.

[Laitch]

No joy.

Does that mean Max didn't respond to you, they responded that none are available, they responded that there was a long waiting period before you'd get one, or that you're just despondent in general?

[Duckbubbles]

There used to be two motorcycle salvage yards within 100 miles of me- both are long gone.
The last gasp option might be adapting coils from another brand of four cylinder motorcycle.  Perhaps even four separate car coils if they are small enough.
Adapting your spark plug leads is a different story.  Long years ago I tried a set of Luftmeister spark plug leads that were built like automotive style but they had a intermittent misfire so I reinstalled the stockers.
Good luck!

Frank