Not trying to be a pioneer here, but as we know all OEM parts for the K's are an expensive deal. 
The idea is to discuss and possibly find viable (read cheap) aftermarket coils. The motivation behind this, is that I've successfully upgraded the coils on my Seca to ones from Dyna, with almost 50% savings compared to OEM.

What's weird about the coils, is that BMW do not provide any resistance values. Haynes says N/A on the dual coils, and Clymer claims BMW do not provide testing procedures or resistance values. It's almost as if BMW knew they were into some black magic and didn't want others to know. 
In this post, Rick says the HT coil shoud measure 40k Ohms: 
https://www.k100-forum.com/t4798-it-s-not-the-alternator-it-is-the-2-3-coil?highlight=coil
Other properties of the OEM coils, are the mounting mechanism and three wire system (+/- and signal), firing order: 1-3-4-2, and I'm assuming 3 Ohm primary coil resistance. The firing order is probably what makes the coils need three-wire setup, but it also effectively disqualifies a lot of aftermarket coils.

Here is the price list for OEM material:

- Ebay (used): from 40$
- Motobins: 134,50£
- Motorworks (used): 38£
- Motorworks (new): 103,20£


Presumed applicable aftermarket candidates:
NONE


Why, oh why, BMW????

Check these out they maybe worth a go http://www.euromotoelectrics.com/SearchResults.asp?Search=Coils

more than a few of us have measured good coils

we all find that the secondary is about 10.6 k on good working ones


yes about 3 odd ohms for the primary coil


there are others around with metal cores and that could be mounted to the frame to do the same thing ....which helps eliminate spikes into the electrical system,

just wont look the same

but I cant think of many automotive ignition systems that use double fire coil packs as a general rule of thumb .

most use single coil and a distributor type system ...or the more modern ones are now usually coil on top of each plug.
although some of the Kawasaki Vulcan machines use double fire coils (2 plugs one cylinder x 2 )  so there is hope

I can think of two double fire coil applications, the first would be the 2 stroke Rotax 582, but I would think that would be very expensive. The second would be a Citroen 2CV, which would be very cheap. Not sure if either is suitable for a K.

bikerboy wrote:I can think of two double fire coil applications, the first would be the 2 stroke Rotax 582, but I would think that would be very expensive. The second would be a Citroen 2CV, which would be very cheap. Not sure if either is suitable for a K.

Last time I was down your way I noticed quite a few Citroen 2CV and Renault 4 cars happily living extended lives. Does the 2CV use a distributor though? The K uses the wasted spark on the 4 cylinder machines which makes me wonder could a coil from a 2 stroke engine produce the required spark?

The 2CV has no distributor and is a 2 cylinder 4 stroke. The points fire the coil which has two HT leads and works also on the wasted spark system.
The Rotax 582 also has two HT leads on one coil.
Link to 2cv coil http://www.franzose.de/en/Citroen-2CV/Dyane/Zuendung/ANR14311/.

seams  Harley  have a similar type dual fire setup



 and about the right primary coil measurements of 3 ohms .....well on the ones I saw

I just did a multimeter check on the primary coils and got 4,3 Ohms. The secondary coils yielded no results...

Most Japanese bike four cylinder use similar coils dual ht s and wasted spark, nothing special there but still maybe expensive? they are also small and i've never heard any complaints about reliability or performance, should be cheap and a safe bet buying 2nd hand. Just up to you electro boffins to determine if the ohms work out? Am I right in thinking that the ICU does'nt give a toss about that? It's only to give a fat short spark? If so use leads to suit the coils?