A couple of factors may be involved with my SL350 K0 lack of output from the alternator. I have always heard that a permanent magnet rotor that is not in use should be stored inside the mating stator. The stator acts as a "keeper shoe" for the magnetic properties of the rotor. If the rotor has been stored open for a long time, it may have lost a lot of its magnetism.
I couldn't remember for sure how the rotor on this bike was stored before I got it, so I went back and looked at some old pictures I had. Bingo! There it was:
The stator was inside a plastic tub, still bolted into the side cover. I would guess they were stored separately for at least five years. I can't remember for sure if I checked the strength of the rotor magnets, but I definitely should have.
The other thing I have read is that a stator can check out OK for coil resistance, and show no continuity to ground, yet still fail to produce power when put into operation. The reason for this is that the coil wire can be shorted inside the windings (loop to loop) yet not to the frame of the stator. This theoretically would not make a significant change in the small resistance reading on the ohmmeter but could effectively reduce the number of windings cut by the magnetic field when the engine is running.
This morning, I found a very reasonable deal on eBay. A seller was offering a 1970 SL350 K0 stator and rotor together, along with the side case that holds the stator,
and the round alternator cover. The harness looks pretty good for being 54 years old, and both the rubber grommets look to be intact, along with the round, plastic plug at the end of the harness. It even includes the neutral switch still plugged onto the harness wire. All of this for US $19.95,
and a 25% discount if I used the seller code he offered. By the time I pay shipping and a royalty to our governor's back pocket, it all comes out to $32.66 delivered price. I went for it.
Even if I find that the stator has a dead short, the rest of the parts are worth more than that. If nothing else, I can make an oil shield by cutting a hole in the round alternator cover for use in dynamic timing. I have always wanted one of those. Now I just have to wait for the parts to show up.
It's probably bad form for me to quote myself, but I did it here for continuity. Here's some follow-up to the last time, when I had popped for an eBay charging system. The parts showed up in good order. For $33.16, including tax and shipping, I got:
A nice LH crankcase cover and the round alternator cover, with the bolts. It could use polish or paint, but there are no cracks, gouges, or even scratches:
The neutral switch was there too, but it will need a drop of solder on the contact point:
Also, the rotor and the stator. The two rubber grommets were in nice shape. This was the original reason I started this thread -- I was searching for the grommets:
The only thing I decided to work on was to replace the brittle and cracked harness sheath, which is normal for a 54-year-old Honda:
With the harness sheath opened up, the wires still even had their white, pink, and yellow colors. The green with red stripe is, of course, the neutral switch wire:
These pictures were after I did some cleaning, but the parts are all very nice. I checked the resistance values on the stator windings, and they checked very similarly to the existing stator already in the bike, from which I was getting zero charge. Here's what I found:
- white to pink = .6 ohms
- yellow to pink = 1.2 ohms
- white to yellow = 1.6 ohms
The proper size of vinyl sheathing for this harness is 10 mm inside diameter. I had some 8 mm (too small to accommodate the four wires) and some 12 mm (too big for the hole in the grommet), so I ordered some 10 mm vinyl from
British Wiring at $1.50 per meter. I got 10 meters at that price, just to feel better about the $10.50 shipping cost.
So, with this stuff on hand, I decided that I wanted to only change one thing at a time to try to figure out why I was not getting charge from my SL350 K0 system. I think it would be fine just to remove the round alternator cover and extract the rotor without disturbing anything else, but I got to worrying about maybe losing the woodruff key or a piece of the sprag clutch in the process. With my luck, it would fall down into the oil drain-back hole and wind up in the lower case half. So -- I removed the alternator cover, the LH crankcase cover, the stator, as a single unit, and then removed the rotor.
With the rotor out of the engine, I did my scientific magnet test on all six of the embedded magnets. This is where I suspend the rotor, one magnet at a time, from a steel hammer, like this:
If the magnet is strong enough to support the weight of the rotor, it is probably strong enough to do its job creating alternating current (at least in my mind).
I was pretty bummed out to find that my existing rotor seemed to have the same strength as the magnets on the rotor I had just bought from eBay. I was at a loss as to why I was not getting any charging. I had hoped to find that my existing rotor had weak magnets. Oh well, I went ahead and put it all back together, with the only new content being the eBay rotor. I reinstalled my original stator.
Now for the part I cannot explain -- I first tested my battery, with the ignition off. It was showing12.3 volts, which is understandable since the bike had run a few miles on total loss (no charge coming from the alternator). Also, the bike has been sitting for a couple weeks with no tender hooked up, and I have started the engine several times just to show some friends that the bike would start and run.
Next, I fired the bike up and connected the same VOM that I had used previously. Before, I could not get anything but a 0 Volts AC reading from the alternator leads, and the DC Volt reading across the battery posts was showing 12.8 volts with the engine running. This value did not change, regardless of engine rpm.
Today was a different story. With the eBay rotor installed, I was getting 18.5 volts AC from pink to either white or yellow (I didn't distinguish which was white or yellow), and 15.8 volts AC from the pink to the remaining wire (which was either white or yellow). This was at idle speed of 1200 rpm. Revving the engine, the reading was going up into the high 50 volts AC range on the meter. When I gave it a handful of throttle, the meter showed 75 volts AC!
At that point, I plugged the alternator white plug back into the harness and buttoned things up. With the meter set to DC Voltage, I was seeing 12.5 volts across the battery posts at idle speed, but now it would go up to 14.2 - 14.5 volts as I revved the engine. This told me that the alternator was working, as was the Sparck Moto Rectifier/Regulator. Again, all I had done was change out the permanent magnet rotor!
I took it out for a 9-mile ride, with the headlight on of course. When I got home, the battery was showing 12.5 volts with the engine shut off. Remember it was at 12.3 volts before the ride. So -- the charging system was running the engine and the head and tail lights, and still putting a little back into the battery. I was not making any special effort to keep the rpm higher than normal during the ride. I had also stopped and restarted the engine twice while I was out.
It's ALIVE. Here are some pictures taken when I was well beyond walking/pushing distance from home:
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