I have not abandoned this projeKt, I swear...
Today, we will make a brick alternator go to 11. Or, 60 actually.
I have a penchant for amps. There's a whole story of why, but in simple terms, I lean toward older vehicles, and older vehicles tend to have underwhelming electrical systems. Nothing makes me do the OCD twitch like having the headlamps dim 10% when I turn on the heater fan.
While I won't be hanging a pair of 150 watt driving lights or a giant dc/ac converter on the bike, a 32 amp alternator seems the bare minimum.
While browsing ebay for a 50 amp unit from a later bike, I happened on the 60 amp alternator from the K1200. "Hey," says I, "60 is bigger than 50, and it's a 30% of the price being asked for the 50 -- I'll take it!" And I did. And, when it arrived, I quickly ascertained that I was a bonehead, and it didn't fit my K100. While it shares the same drive and the same 3-eared mount style, the bolt spacing on the mount is about 1/2" bigger than the K100 alternator.
I went back to looking for a deal on a 50 amp. The only one I found that was close to as cheap as the K1200 alternators was ugly, "sold as is, not tested, no guarantee of function." But, I noticed something -- it looked like the K1200 alternator, not like a bigger 32 amp alternator. "Hey," says I (I talk to myself a lot), "maybe the cases are common, and only the front half has different mount dimensions?" I decided for the price, I would take the gamble. Worst case, I would have a 50 amp alternator core for a rebuild.
When the 50 arrived, I set it next to the 60 and took a look. Even without measuring, I could see the back of the case was identical. On the 60 the front, or mounting end, was similar but looked slightly deeper.
So, time to dig in...
Here are the three alternators, from left to right 60a, 50a, 32a. The differences and similarities are obvious.
The two bigger alternators...
First, remove the drive pulley, or whatevah you call it. An impact gun will make short work of this, or you can carefully clamp the pulley in your vise and use a socket.
Then, remove the screws that hold the front bearing in the case. I found them to be quite stuck, so I gave them a good rap or three with a flat punch and a BFH to break the corrosion you always get with steel screws in aluminum.
Then, remove the three small screws holding the rear cover, unclip the cover and remove it.
Next, take out the two screws and remove the voltage regulator. This isn't strictly necessary, but it prevents accidentally breaking a brush, and makes it easier to remove the armature.
Now, take out the 4 bolts that hold the two halves of the case. The bolt that is next to the terminals is hard to get to with a socket, so I just used an end wrench. A wobble would probably get it too.
Now, use a screwdriver or similar to carefully prise the case halves apart. The armature will likely come out with the front half. On the 50a case, the armature then was easy to pull out of the front case. On the 60a, the bearing was a bit tighter, so I had to employ some percussive maintenance to separate the two.
And presto, I've broken it!
Now, to that slight length difference noticed earlier, here's how it plays out when the 50 amp case front is placed on the 60 amp alternator.
While this looks like it could be a problem, it isn't. What you see exposed are the outer bands of the stator, which are marginally exposed anyway. The difference amounts to roughly 0.120 inch. Armed with my digital caliper, I made a quick run to the hardware store and found small washers, that in a stack of three made up almost exactly the needed dimension.
Assembly, as they say, is the reverse. I used some thread locker on the four case bolts to compensate for the small reduction in thread depth contact. I also cleaned the contact rings where the brushes ride with some 0000 steel wool and WD-40, and scuffed the rust off the outside of the armature and inside of the stator with some 600 grit paper. And finally I cleaned the 50a case front in the media blaster just because I could. Here's the final product...
And here it is positioned in the bike, with the battery tray behind it to show the fit. A bit larger than the 32a, but still plenty of room.
I'll put new terminals on the leads when I get that far in reassembly. I will likely upsize the feed wire for the battery as well, just to avoid any problems with resistance in the older, smaller wire. It would be a shame to burn this thing down after doing all this work!
Bottom line -- I have a 60a alternator in my K100 for a total investment of about $80. Not bad, says I... :2thumbup: