50 Amp Alternator Upgrade Kit
This is a common upgrade for K bikes and relatively easy to do. It takes roughly an hour or so and the kits I have include everything you need: a working low mile 50A alternator (over $900 new from BMW!), heavy duty electrical cable, terminal and complete, easy to follow instructions. You don't need to be an electrical whiz to do this.
The original K bikes came with a 32 Amp alternator. This is more than adequate for running the bike and minor electrical accessories but once you start upgrading to a higher wattage headlight (don't do this unless you install headlight relays first), using a heated vest or jacket liner or running auxiliary fog or driving lights the alternator can become overtaxed and the accessories will start draining your battery. In 1993, BMW start started upgrading K bikes to a 50 Amp alternator which provides ample extra electrical power for adding electrical accessories.
The table below shows which bikes came with a 32A alternator and which bikes came with a 50A alternator:
It's also very easy to tell if you have a 32 or 50 amp alternator by visual inspection. The alternator is located in front of the radiator coolant reservoir on the right side of the bike. There's a triangular vented black plastic cover over it. By looking at the rear end of the alternator you can tell which one your bike currently has. The rear of the 32 amp alternator is metal. The rear of the 50 amp alternator has a round black plastic cover which, if it hasn't worn off, will have "50" on it. (See picture above.)
Better yet, the heavy 50 amp alternator can be shipped in a Priority Mail Flat Rate Box which keeps shipping costs down.
If you'd like a 50 amp alternator, you can email me by clicking this link:
NOTE: You may want to consider installing new rubber bushings that cushion the alternator drive when upgrading your alternator. The BMW part number for them is 12311464877.
Coolant Reservoir: If you have an early K75 or K100 that has a hose with hose clamps on the side of the coolant reservoir (like #1 below) then you will also need to replace the coolant reservoir as the 50 amp alternator is slightly longer than the 32 amp one.
Type 1 (hose with clamps) won’t work
Type 2 (plastic window, hose in front) will work if you nudge the front of it over to the right a bit
Type 3 (plastic windows, hose in back) will work