BIG alternators for BMW Airhead motorcycles

Really BIG alternators for BMW Airhead Motorcycles
15-D
reallybigalt.htm
© Copyright, 2011, R. Fleischer

Besides the modest output improvement (comparatively!) of the Omega and EnDuraLast, and especially in the past, there have been quite a few truly large alternators installed
on BMW Airhead Motorcycles (and on the /2 era BMW motorcycles too!). This article shows a photo of some installation, and some discussion below that photo.

Please refer to Article 15-A and 15-C for information on the Omega and EnDuraLast aftermarket alternators... and a discussion of the capability of the stock Bosch alternators.

There have been installations that attach the alternator to the crash bars.
Generally speaking, that does not work out well over time, unless the crash bars
are modified to be beefy and substantially supported.

Note the bracketry/mounting directly to the engine case! Note the angled post for the
tension adjustment.
Cut in case for belt passage. Can be left or right side.

There are several ways of doing this type of conversion; here is the basics on how I have done SEVERAL....on R60/2; R75/5, R90/6, etc.:

1. Disconnect battery. Remove fuel tank. Unplug voltage regulator. Remove the front cover, so you can see the stock alternator.
2. Remove all of the alternator parts; and using appropriate HARDENED threaded tool (not a jaw puller!!), remove the rotor. You will need a rotor,
      unless you are an excellent machinist at turning precise tapers on a lathe. Sell your rotor if in good condition, and get one that needs rewinding, as you
     will need the taper portion (at least).
3. Removing the diode board mounts (if the removable type).
4. Modify the rotor so it has a V-belt PULLEY attached to it. You can use a toothed belt also. Be careful not to damage the taper. The only thing
     you really need is that taper, and a pulley affixed VERY squarely and sturdily to it. I like the pulley to be SMALLER in diameter than the new
     alternator's pulley, so that the engine will run the alternator at a bit faster than engine rpm. The pulley/rotor-taper modification MUST be done with strength,
     neatly and very squarely, and I did all of mine on a jig on a drill press or in a lathe or in my mill. You will have a choice on what type of pulley,
     and how closely towards the crankshaft it is mounted. Think about it all before committing yourself.
5. Select the proper alternator.   This is actually part of the above step 4. Try to find an alternator that mounts nicely (and strongly!) to your engine
     and to whatever mount(s) you make for it. The alternator can pull a lot of engine power, so things must not vibrate nor bend. I suggest a small diameter
     alternator, with built-in or built-on cooling fan(s).   Consider the direction of mounting and the direction the alternator fan blows the air in relationship to the
     direction of your motorcycle's engine rotation!!
6. Use a large battery if possible...such as a car type. It will better absorb the alternator capability.
     This installation is ideal for a sidecar rig, where the battery can be placed in the trunk of the sidecar, where its weight is an advantage there.   You can
     COOK a motorcycle-sized battery from excessive charge, so it is a good idea not to run the bike battery down too much, if that size battery is what you will use.
   The commonly available 28 or 30 ampere-hour flooded motorcycle batteries will usually work OK.
7. Use a self-contained alternator, of the one terminal type (one additional smaller terminal to drive the dash GEN lamp is fine). Use heavy gauge wire
     to the battery and do have a good ground too.

AND...for those of you that want the neatest, near ultimate installation, I offer this:

Rev:
05/22/2010: clean up article
08/31/2010: add more photos, permission from Albert Lindberg.
Also add more commentary, edit information #2, 3, 4, 5, 6, 7.
01/07/2011: add photo of Greg's 800 watt alternator conversion

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