Sunday, December 11, 2022

SOLD! #forsaleatscottiesworkshop 1991 R100GS, 16k miles, 1 owner, top end rebuild with new rings, clutch replacement, bevel drive and swingarm rebuild, new Conti trailattack3, BMW factory screen, AGM battery. Asking $14500.

Risks associated with repairing a faulty ignition switch

All antique and vintage--and some classic--BMWs share a common ignition switch system. Using what is often called a "nail key" because of the relative ease at which one could steal literally any vintage BMW armed only with a ten-penny nail. (In the cases where a nail wasn't handy, any twig or stick off the ground would easily suffice.) The pin-shaped nails featured an beautiful art deco handle and a pin with detent slots, that engaged a ball-on-spring mechanism in the switch assembly to hold the key vertically in one of two positions: ignition off or ignition on. On the magneto-equipped bikes (nearly all of them except coil-powered models such as the R26-R27), one wire terminal of the board shunts a terminal to ground when the key is off (and isolates it when the key is on). This terminal is connected to the condenser positive, killing the ignition when grounded.  On coil ignition-equipped bikes (/5 Series),  wire terminal #15 provides battery + current when the key is on. Besides moving vertically, the key can also be rotated around the pin, and when depressed into the "on" position, can select one of three headlamp switch functions. In position one, when the nose of the key is facing left, the headlamp is on. In position two; headlamp is off. And in position three, tail lamp/city lamp is illuminated. 

In case you thought only BMW owners were plauged by poor switch design and easy motorcycle theft, you might be interested to know that some other motorcycle brands used this configuration, including Laverda. 

Shared by many vintage BMW, the ignition switch board design is flawed such that it ages poorly and is difficult to rebuild.  The ball-on-spring mechanism is sandwiched between the switch board and headlamp shell. The board is held in by bendable tabs that are integral to the headlamp shell itself. Unbending and bending the tabs may result in the tabs breaking off.  The subassembly which contains the tabs  can be replaced but only at great expense as the entire headlamp needs to be removed from the bike, speedometer and all wiring removed, disassembled and bead blasted to bare metal. The old subassembly can then be ground out and a new one welded in, and then the headlamp repainted. For about $1000 we can buy a brand new headlamp assembly - if the suppliers in Europe have them in stock. This often includes everything but the speedometer. 

Switch units generally fail in one of two ways. Either the switch fails to to stay engaged (the ignition is difficult to turn on, or won't stay powered on), or the headlamp switch is difficult or impossible to operate. In the case where the ignition won't power on, one can attempt to press down on the key and rotate it slightly, partially or fully engaging the headlamp switch. This puts some sideload on the key pin and helps it stay engaged. In the case of faulty headlamp switch operation, one can remove the key and flip it 180 degrees. This method engages the key in an seldom used position and may help it engage better. 

If these workarounds don't help we may be forced to perform repair or replacement. 

If a replacement headlamp is not available, we may need to rebuild the switch assembly and assume the risks associated with that - breaking a tab.  The estimated labor to replace the switch --if all goes well and a tab doesn't break --is 2 hours, which includes disconnecting the harness from the switch and removing the headlamp from the bike. The switch board and switch assembly run about $225. However, and it's a big however, if a tab breaks, then we must replace the tab subassembly, prep, rebuild, repaint, install the headlamp in the bike--about 1-2 man days.  Yes, I know, kind of nuts. Headlamps are tough to restore.  That's why I'm a big fan of those new units. 

An alternative to the BMW switch board is a kit offered by Rocky Point Cycle which eliminates the nail key and the BMW switch board and replaces it with a traditional ignition switch with a normal key. It retains the black sliding door and chrome cover; one slides open the black door, inserts a normal looking key and powers on the ignition (similar to any normal ignition key switch.) For more information see Rocky Point's site at