I think I'm having trouble with my 1 / 4 cyl HT coil, bike is runing powerless and missfiring, plugs are shooty and primary coil has droped to 1.5 ohms. Waht are the options for aftermarket coils?.
In the mean time, as the problem begun during a heavy rain ride, I´m trying to restore primary resistence by oven drying, any one has experience doing this? I´m keeping temp under 85ºC and for oven time of two ours resistence has raised to almost 1,9 ohms.
I´ll appreciate your kind answers
Best regards
JAP

Supper is in the oven and will be ready in 15 min!
Sorry, I didn't have any answer to your question but this was too funny not to reply.
The idea of drying the coil in the oven is certainly good.

Being electricaly inclined I would say that if drying them in the oven makes them work then water is where it should not be. There is most likely cacks and I would replace the coils however possibly a good clean with prepsol or acetone and then a coat of polyeurathane varnish or similar may seal them and extend the life a bit.

good thinking jap ....im sure this is not the first time this has happened ...but we seem to see the secondarys going open circuit ..or high resistance .

i would be doing what k freak has suggested and coat them with a varnish .

many years ago i worked for "cafe bar" and we needed to "dry out" heating elements to keep insulation resistences high as they were attached to the mains ...to do this we ran them in series combinations so that about 1/4- 1/2 the current would flow through them ...still with some heating effect at about 50-60 degrees c.

the aim was to get an extreemly high insulation factor ...in excess of 10 megohms this may have taken up to several days to acheive .

lower resistance indicates to me that some corrosion has already occured between the windings though ....and cetainly some of the enameling on the coil may have already deteriorated .

i wonder if you measure between the secondary and primary ...if there is some lower value leakage (less than 2 meg ?) the reason for looking for this is to establish if there is an internal tracking between the coil sections ....primary to secondary ..

in any case it would be wise to try to get another coil but i dont have enough experience to be able to suggest which one , other than the bmw relacement .

at least we do know what the values should be .

good luck ....i would be interested to see what happens to this long term . but i think you are doing the right thing .

The oven trick partially worked and resistance raised up almost 0.5 ohmn afther 8 hours at 85ºC this made the bike run a bit better but not enough. At the same time the search for the new coils resulted as follows: BMW dealer 234U$D/pz, Euromotoelectrics 149U$D/pz, Rockauto 118U$D/pz. Coils arrived last week and bike is running fine, tomorrow will made a 200km ride test.
Now that the new coils are here I´ll try the oven at 100ºC and see what happens.
Best regards
JAP

fingers crossed for you jap ...

The oven trick is a good one, the other thing is if after the good bake you have access to a vacuum pump is put them in a bell jar on the pump suck out the air and leave them under vacuum for a few days to really pull all moisture out. Then let the air back in and get some insulation varnish definitely not black varnish and pop the coils back in the vacuum chamber but submerged under the varnish and suck them down again.

As the vacuum drops you will see small bubbles coming out of the cracks in the coil which is the air in there coming out. As the vacuum goes lower you will see the varnish start to boil as the solvent flashes off. At that point stop and allow the air back in to the chamber using the air pressure to force the varnish deep into the coil.
That should fix it, I used to do that impregnate HT transformers in the lab in another life.
Regards,
K-BIKE