XS650 ROTOR

I just put another alternator rotor on my '78 XS650, and it's charging
fine now. I don't like to spend money and I know that the rotor is a
weak part of the XS650's charging system. Given all that, I'm thinking
that I should be able to rewind the old rotor and save it for when I
need a quick replacement. How do the pros get these things apart? They
appear to be pressed together, and if they must be pressed apart, where
are the press points. The service manual has nothing on this. Is there
a web site that can show how stators and rotors are rebuilt? I am
pretty much a "do it yer selfer" with my hobbies if possible.

As an after thought, has anyone come up with a more reliable and/or
higher output replacement for these bikes?

Also, thanks to Krustykritter for all the good info I've seen here!!!

 

I think you mean the *stator*. That's the part with the copper
windings. The rotor is the rotating steel part with the magnets in it.

It's probably beyond the capability of the do-it-yourselfer to do
anything about the rotor. My eternally-broke friend tried rewinding the
stator on his GS-1100G a few times. It seems that the enamel insulation
on the electronic parts store copper wire he bought couldn't stand
being immersed in hot oil. The coils kept shorting out.

He also tried building rectifier regulator units from a circuit I gave
him. It was an educational experience for him, as he made some eroneous
assumptions about the reverse voltage requirements of the diodes and
the necessary wattages of the reistors in the zener diode circuit...

Google for Electrex USA's web site. They make aftermarket stators and
improved rectifier regulator units with two silicon control rectifiers
instead of one.

 

My broken rotor is one of those electromagnet types with the coil of
wire inside and the heavy soft iron shell. It doesn't have the
permanent magnets. No oil bath. I suspect that the wire is broken-
there is no complete circuit between the slip rings or from slip rings
to ground. Stator is fine.

Another question- Does it make any difference how the white wires
from the stator are arrainged in the connector, so long as they are in
the " white wire side" of the connector? I just got a good stator that
has no connector on it(smushed by bigfoot). I don't think it should
make a difference but I see that the service manual lables them each
"u" "v" "w" in the drawing. And how would you tell which is which if
looking at the stator? what do those letters stand for?

Ya know what- I was thinking about building one of those
rectifier/regulator units for a winter project from plans I saw
somewhere on the net that uses Radio Shack parts if I can find it again.

 

Just an idea:

I've seen talk of some who replaced the alternator on the xs w/ a
magneto from a Yamaha DT250 dirt bike. Getting rid of the alternator
would simplify your voltage regulator circuit as well as allow you to
run without a battery.

Of course, that may not be what you want to do at all, but the idea
appealed to me as a way to strip some more weight out of these portly
bikes. I didn't do it on the current project, but most likely will try
it on the next XS I do.

-Vin
T. E. Motorworks

 

Where did you see this? I would like more info on this if you can
provide it.

Thanks
Brian


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Problem is, the average running electrical load on a single headlight
street bike (including high beam, tail light, brake light, turn signals
flashing, maybe running lights up front, and instrument lights) is
about 100 watts.

That doesn't include battery charging current and whatever current is
needed to run the ignition system.

Don't forget that streetbikes have electric starters and the DT250 was
a kick start machine. It didn't even really need a battery except to
meet state vehicle code lighting requirements that said the battery had
to keep the *tail light* lit for half an hour.

The alternator has to produce a lot of juice to keep a bigger street
bike battery charged up.

I dunno perzactly what the output of the lighting coils on a DT-250
was, but I doubt that it was 100 watts. Maybe it was 60 or 70 watts at
most.

Been there, done that. Learned a lesson or three...

That's why I recommended swapping a dirtbike permanent magnet
alternator for the heavy excited field alternator on a Suzuki GT-750
water buffalo that we were modifying for daylight endurance racing. We
didn't need a headlight, and I figured that we could shorten the engine
and get more lean angle with a compact PM alternator.

The amateur machinist who installed the rotor on the end of the crank
didn't have much sense about what it would take to adapt the tapered
parts together though. He had to somehow mix parts of the original
equipment centrifugal starter with the dirtbike rotor, so he just
countersunk some holes for 1/4" phillips screws and expected that
half-assed rig to stay together for hours and hours at several thousand
RPM.

It didn't work. He should have rivetted the parts together and used
press fit dowel pins to locate the parts in relation to each other. His
bolts loosened up. We removed it and ran a total loss ignition system
off the battery.

 

Well, since most street bikes are going to be battery and coil systems,
the
permanent magnet alternator coil usually used for the energy transfer
magneto can be used for battery charging and general electrical loads
instead. That would give 1/3rd more power.

When I first suggested using a permanent magnetor alternator what I had
in mind was a unit off of some older 1960's Honda street bike, and when
my machinist type buddy produced the dirtbike alternator, I figured we
were in trouble, either he'd have to return it to whoever he got if
from, or we'd have to convert it from 6 volts to 12 volts or run 6 volt
system on the race bike.

So I researched the subject and found that the output of permanent
magnet alternator would be a function of the RPM of the engine, the
number of coils in each winding and the flux density of the magnets. We
had no way of knowing what the flux density was, so my machinist buddy
suggested that we just wind as many turns of finer wire on the coils as
possible to get more voltage. He said that we could then measure the
voltage output at high RPM and remove as many coils as necessary to
reduce the voltage.

We didn't know about how small low-powered alternators' output voltage
was "clamped" to battery voltage or just a little more. We were amazed
that the little re-wound alternator was able to push 1 or 2 amps of
charging current into the battery.

But we wanted MORE current than that. It seemed that we also had an
electronics engineer on this blundering design committee and he had
suggested using a Chrysler multi-fire ignition system to fire all three
coils simultaneously three times per revolution! Believe it or not,
this system *worked*. The engine ran and put out a lot of power, enough
to be dominant over the 750cc 4-strokes---while it lasted.

But the Chrysler system drew a lot of amps. It drew about 30 amps when
the engine wasn't running and the current dropped off to about 7 or 8
amps at higher RPM. We wanted to get more current out of the alternator
to keep the battery charged, so I came up with the solution of using
TWO 3-phase full
wave rectifiers instead of one. That cut the resistance in half and
doubled the current available for charging. We had no voltage regulator
at all, since the alternator output voltage was so closely tied to
battery voltage.

Our entusiastic blundering engineer and our enthusiatic blundering
machinist was accompanied by a generally enthusiastic blundering madman
who was ripping all the existing wiring out of the wiring harness to
save a few ounces of weight, and I was the enthusiastic electrician
trying to wire up the electical system while the enthusiastic madman
was ripping wires out and turning the K-mart coils around backwards.

I had my doubts about whether the Chrysler ignition system and the
K-mart coils (and the Thunderbolt CDI that the enthusiastic engineer
had insisted needed to be on the bike) would last for the six hour
endurance race, so I wired up a spare stock ignition points plate, just
in case.

When I got to the race track on Saturday morning, the enthusiastic
blundering crew had everything all torn apart trying to figure out why
the engine kept cutting out on one cylinder. It seems that the special
8-gallon endurance racing gas tank was touching one of the ignition
coil terminals that the blundering madman had turned around backwards.

Everybody cheered when I arrived, because nobody had any idea of how to
wire up the points plate using the aircraft modular terminal blocks I'd
installed.

The bodged up permanent magnet alternator rotor was falling apart, so
we figured that the Chrysler ignition system would drain the battery
too fast and therefore we installed the points plate and ran a total
loss system for as long as the engine lasted.

That wasn't long, since the water pump couldn't circulate any water
through the cooling system. It was all plugged up with an excess of
Bars Leak. The center piston melted, there was a hole in it, it seized
and broke the connecting rod.

 

Hey Brian,

I have only a limited amount of info on this, having never done it.

Here's one discussion thread about it:
http://www.xs650garage.com/bb/index.php?board=8;action=display;threadid=1749

And another somewhat less useful thread:
http://www.xs650garage.com/bb/index.php?board=8;action=printpage;threadid=510

-Vin

 

Yeah, absolutely. I should have mentioned, but failed to, that my
research into this was for a bike where I was looking to eliminate the
battery and a large portion of the wiring. I must admit that I
generally set my bikes up with out turn signals, remove the starters
and kick start them only, and don't run any accessories.

So, admittedly it's a small portion of XS owners that to whom my idea
would be reasonable. Your comment about the permanent magnet
alternator from a dirt bike, or another street bike is probably a
better idea for the majority of owners. The thread references I posted
above make mention of swapping in an RD/RZ alternator to this end.

For those few though, it's interesting to note how much of the
electrical system there really is to remove on the later bikes. I'll
post some pictures on my site soon. I prototyped a new harness for the
'81 xs I am working on now that is just about the bare minimum to run
the bike - connections to voltage regulator and (stock) alternator,
crank sensor and ignition box, head, tail, and brake lights, and
ignition and kill switch. If you count the relays, unnecesary
features (IMO, reserve lighting unit for instance), battery box,
gigantic stock tail light, and the original harness itself, it removes
18 lbs of weight. The new harness weight 1 lb. You then have to add
back in the weight of the replacement tail light and new battery box.
However, in my opinion, a net loss of even 10 lbs as well as the
elimination of an awful lot of complexity is worth while for someone
doing a stripped down cafe racer or the like.

-Vin

 

Years ago I was workig at a shop that specialized in oddball alternators,
staters and the like. We had a brushless, field excitable alternator come
in and I diagnosed that the rotor coil was open. I tried to order the part
but no parts available. I told my boss about it and he said, let's go fix
it. He unsoldered the outside lead and started unwinding. About 1/2 way
through the outside layer, the wire broke and there was the open. He took
off a few more feet, soldered the wire back, coated the thing in red
glyptol and baked it. I it back together, put it on the test stand and it
worked just fine. I asked him about the lower resistance and he said we
took off about 1-2% off the coils resistance and it wasn't enough to worry
about. I asked him how many he had fixed like that and he said about 2
dozen and none ever came back. BTW the alternator had a built in regulator
and rectifier. I worked there for over 5 years and I never did see it back
again. The alternator was from a commercial account and we fixed all of
their alternators and starter motors.

Another common failure is that the wire will break right where in attaches
to the slip rings. If you are lucky it will be the outside layer and all
you have to do is unwind a turn or three, scrape some insulation off,
resolder it and you will be in business again.

Yes, those clamshells are pressed onto the shaft. Pulling them off without
destroying the shaft or the shells is not easy.

YMMV

r