R100GS Dyna Coil Upgrade

How many times have you heard of people working for days or even months trying to track town an intermittent stumble or hard starting problem on their air head BMWs, only to find that a defective coil was at the heart of the problem? As our airheads age the epoxy that separates primary and secondary windings becomes brittle, and if it cracks, it may not generate sufficient secondary voltage to fire the spark plug. The problem seems common enough to warrant proactive steps to avoid it. Rick Jones at Motorrad Elektrik recommends the Dyna coil, and I found the installation very straight forward and the results indistinguishable from the original. Except, hopefully, in long term reliability.

The BMW coil lives up under the fuel tank just behind the head tube, and the first job in making the swap is to remove it. Pull the two primary leads off the spade terminals, and remove the two socket head cap screws that hold it to the frame. Pull the plug wires off the coil if you’re going to reuse them, otherwise pull the plug leads off the spark plugs.

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Dyna Charging System Monitor Install

A while back I had the misfortune to have a dead battery in a grocery store parking lot in Moab, Utah. The bike had been blowing fuses every time I tried to use the turn signals, and after putting up with it for the first few days of a two week vacation, I just left the burned out fuse in place. I didn’t have any dash lights or turn signals, but otherwise the bike ran fine. But when the battery went flat, I knew there was something else more seriously wrong.

A bump start got the beast running again and back at the motel Mail Box Bruce let on as how the alternator wouldn’t make much charge if the alternator warning light wasn’t coming on. Seems the current to the exciter coil of the alternator runs through the warning light, and if there’s no exciter current, there’s no juice for the battery. So I ripped off the tank and started poking around looking for the short circuit. I’d been having problems with the electric grips since Baja, so those were the first to be disconnected. The turn signals worked fine until the bike was started, and then the fuse would pop. I went on disconnecting and checking, even going so far as swapping out the warning light assimilator with one from Gene’s bike. No joy.

So it was back to running with the fuse in, and being very careful not to hit the turn signal switch. After I got home I pulled the fairing and found that one of the turn signal idiot lights had backed out of the holder and was shorting out on the speedo cable. That was easy to do since the leads were uninsulated. A little liquid insulation fixed that, as did rotating the lamp 180 degrees. So now you know where to look if this happens to you.

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