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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, ring 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, heated grips, etcetera 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 started upgrading K bikes to a 50 Amp alternator which provides ample extra electrical power for adding electrical accessories.

My 1993 K1100LT came from the factory with a 32 amp alternator.  After performing this upgrade I'm now able to run a higher wattage headlight bulb, a pair of 70 watt fog lights, an MP3 CD head unit, a heated jacket liner, heated boot insoles, and heated grips with no problems.  If I tried running all of that with my old alternator my battery would be dead before I could ride 100 miles.

The table below shows which bikes came with a 32A alternator and which bikes came with a 50A alternator:

K Bike Model

32 Amp Alternator

50 Amp Alternator

K75

Model year 93 and earlier

Model year 94 and later

K75C

All model years

 

K75S

Model year 93 and earlier

Model year 94 and later

K75RT

Model year 93 and earlier

Model year 94 and later

K100

All model years

 

K100RS

All model years

 

K100RT

All model years

 

K100LT

All model years

 

K1

All model years

 

K100RS(4 Valve)

All model years

 

K1100LT

Model year 93 and earlier

Model year 94 and later

K1100RS

 

All model years

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.

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:

mailto:smithduck@gmail.com?subject=K Bike Parts: 50A Alternator Upgrade

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.  You’ll need three of them and the total cost will be about $20.

 Coolant Reservoir: If you have an early K75 or K100 that has a hose with hose clamps on the side of the coolant reservoir 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

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