Really BIG
alternators on Airheads
15-D
reallybigalt.htm
©
Besides the modest 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 one, 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 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 a primo 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 rubber types), is a PIA, so
leave those if you want to.
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
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 you make for it. The alternator can pull a
lot of horsepower, 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 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. 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 work OK.
7. Use a self-contained alternator, of the one terminal
type (one additional smaller termiknal to drive the dash GEN lamp is fine).
Use heavy gauge wire
to the battery and do have a good ground
too.
Rev:
05/22/2010: clean up article
© Copyright,
2010, R. Fleischer