1981 xs650 rotor

Im not getting spark from my bike. I bought a used ignition unit(off of
a working bike) thinking this must be the problem but it didnt help.
I know the coil is good.

Only thing left is the rotor so I tore apart the rotor assembly and
noticed the the rotor does not have amuch of a magnetic field. Is it
possible to recharge these at home or am I stuck getting another one??

 

possible to recharge these at home or am I stuck getting another one??

http://www.yamaha-motor.com/yds/partscatalog/consumer.asp

Got brushes?

According to this Yamaha parts catalog, the 1981 XS-650 has an *excited
field alternator* which uses *brushes* to energize the rotating
*electromagnetic* field in the rotor by taking a small amount of DC
current from the battery and controlling that current with a voltage
regulator...

Excited field alternators will only have a very weak residual magnetic
field which can sometimes be used to "bootstrap" an excited field
alternator into producing electricity even when the battery is dead or
not in the circuit...

So weak magnetism is nothing to worry about...

 

of a working bike) thinking this must be the problem but it didnt help.
I know the coil is good.

noticed the the rotor does not have amuch of a magnetic field. Is it
possible to recharge these at home or am I stuck getting another one??

Have you checked your Hall Effect sensor for continuity? It's the black
plastic thingumbob on the alternator stator...

In 1980 Yamaha started putting factory electronic ignition in the XS
650's. The charging system has a small magnet in the rotor that passes
the "Hall Effect" ignition signal pickup unit. A magnetic field from
the small trigger magnet in the rotor passes the pickup and induces a
small voltage that triggers transistor switching to send battery
voltage through the coils and eliminate mechanical points and ignition
advancers that can wear and change.

Other electronic ignition systems, like Suzuki uses, for instance, have
a *stationary* magnet at each pickup coil, and there is a small
electrical current running through the pickup coil. When one of the
non-magnetic teeth in the multi-toothed ignition rotor (also called a
"reluctor" passes the pickup coil, this causes a *change* in the
electrical current in the coil and switches off the appropriate
transistor in the ignitor box...

 

If you've got an electronic tach, you can tell quite a bit just
by watching the tach needle as the engine cranks over.

If the Hall sensor and ignition control unit are working properly
you should see the tach needle move as the engine cranks. If there's
a problem in either of these components the needle stays flat.

In a moment of shining stupidity, I recently managed to pinch the
lead from the Hall sensor to the control unit when I reassembled
the engine. Sucker ran fine until the casing cut through the
insulation and grounded out the wire.

While I was at it, I'd also check that I was getting +12 volts
into the coil and check my plug wires for continuity.

 

OK... I was able to do a little checking again.
I did an ohm reading on the pick-up coil and compared it to what the
clymers manual says was good and it was with tolerance. I then took off
the pick-up coil(hall effect) and waved a magnet next to it very fast.
This time I have spark.

So do I have to replace the slip ring assembly(which contains the magnet
to fire the pick-up coil) or is there something I can do to fix this??

 

clymers manual says was good and it was with tolerance. I then took off
the pick-up coil(hall effect) and waved a magnet next to it very fast.
This time I have spark.

Well, that proves that your ignitor box, the wiring, and the sensor are
OK, only the trigger magnet is suspect now...

magnet to fire the pick-up coil) or is there something I can do to fix
this??

I looked up the part number for a 1981 XS-650SH rotor. It's
3G1-81650-10-00

I used that part number to check the price at www.ronayers.com and they
want $321.65 for a new one, but they don't have a new one, it's
"discontinued". The Online Motorcycle Fiche at http://www.hlsm.com/
wants $422.11 for a rotor...

Maybe you can re-magnetize the trigger magnet, as you asked in a
previous post. Magnets are made of a certain type of iron which can
have all of its north and south poles aligned in one direction by being
exposed to a powerful magnet...

Magnets lose their magnetism by being over heated, stuck by a sharp
blow, or being exposed to an electromagnetic field that constantly
reverses in polarity...

Maybe the latter case is what made your trigger magnet weak...

But, if you have a really strong magnet handy, just placing it next to
the trigger magnet so it attracts itself will help the weaker magnet
realign the north and south poles in the same direction...

Riders who have installed bicycle speedometers on their motorcycles to
get really accurate speed readings and distance readings say that you
can get some really powerful small magnets from Radio Shack...

 

I appreciate the replies... I do have some rare earth magnets that are
close to the diameter of the trigger magnet. I guess I will try and
drill out the old magnet if it is iron.

 

are close to the diameter of the trigger magnet. I guess I will try and
drill out the old magnet if it is iron.

Red or green Loctite will hold the magnet in place and it won't come
adrift. You may have to slot the mounting holes in your Hall Effect
sensor to adjust the ignition timing if it changes...

 

Even if it's theoretically possible, it seems really odd to have a
magnet become de-magnetized, particularly if this happened suddenly.

I'd make sure the old one was really bad before I broke out the drill
and destroyed anything. Other things that might cause the same symptoms
could be a grounded out wire or something that had shifted position.

As I'd said in an earlier post, I pinched a wire between the Hall
sensor and control unit when reassembling the engine. A problem
like this could look completely OK when things were disassembled.

Unless you'd recently done something that would cause a magnet
to become demagnetized I'd be kind of suspicious of this explanation.

 

I recently bought this bike at an auction. There was several small items
that needed fixed.

Ive looked closer at the alternator rotor and what I thought was the
trigger magnet was not!!! . I can not find any trigger magnet on the
face of the rotor so Im wondering if the magnets for the alternator
triggers the pick-up coil.

I was hoping someone has run into this problem before and can give me a
good idea what to do/check.

 

Demagnetization used to happen to old Brit bikes with L***s energy
transfer magnetos. P****e of D*******s tales won't help with the
present problem, though. There was some kind of gizmo in the Brit bike
dealers that would remagnetize them...

 

trigger magnet was not!!! . I can not find any trigger magnet on the
face of the rotor so Im wondering if the magnets for the alternator
triggers the pick-up coil.

As I said previously, the alternator rotor would only have a very weak
residual magnetism because it's an excited field type. If the pole
pieces on the rotor were triggering your spark, you'd be getting
multiple sparks per revolution...

But, looking at the drawing on the web parts fiche, I see that there
are some *slots* on the end of the rotor, which may have something to
do with triggering the spark...

My old T-Bird had a Hall Effect distributor which had a sheetmetal
rotor that had very wide slots alternating with very wide "teeth"...

The coil would produce one spark only when the ignition switch was
turned on and one spark only when the ignition switch was turned off.
but that didn't prove whether the sensor coil was any good, it just
proved that the ignitor box and the coil were working...

On the other hand, the reluctor rotors used by many other cars and my
Suzuki have very narrow teeth, they aren't magnetic at all, they cause
a change in the impedance of the trigger coil as they pass the fixed
magnet and sensor coil assembly. That type of motorcycle ignitor box
can be checked with a flashlight battery. Same deal, one spark when the
battery is hooked up, and it better be the right polarity hookup...

You might want to do some researching on Hall Effect ignition systems
to be sure whether or not you're supposed to get a voltage from the
ignitor box to the trigger coil or not. Maybe your Clymer manual will
say something about that...

 

But OTOH, triggering a steenking little Hall effect sending unit
is a lot different than driving the whole friggin system. Even
on a magneto, I'd be pretty surprised if it wasn't a slow process.

My bet might be something more like the Valeo starter problem where
the engine gets overheated, the glue fails and the magnets leave
their homes to go exploring.

 

Found this site:

http://www.xs650garage.com/

You might ask there.

Re the alternator magnets as a trigger:

Basically, you'd probably want one pulse per revolution of the crank
(assuming a wasted spark setup). I guess it's not impossible that
the alternator magnets could be triggering it but that seems like
an awful lot of wasted sparks unless only one spot on the rotor
was set up to trigger.

Bransden also seems to offer an aftermarket ignition.

I'm curious what you find out.

 

OK. I got curious, did a little digging and found this:

http://650motorcycles.com/1980SG.html

Shows both the rotor with the trigger and the earlier rotor
without a trigger. 650motorcycles.com seems to have a pretty
good search engine. You also ought to take a look at micapeak.com,
which I think has a 650 mailing list along with lists for lots
of other bikes.

 

Boy now I am alittle unsure. I see where they show the trigger magnet
and I see it on mine also but I was going to drill it out yesterday and
put the drill up to it and turned it on for just a second, It sure looks
like copper to me. I just scored the face slightly.... guess I will try
and drill it out and replace the magnet.. worst case is I would have to
replace the rotor.. I remember somone saying something about the stator
intensifying the magnets.. is this correct because I think by stator is
bad.. I have to check some more though...

 

magnet. I remember somone saying something about the stator

is bad.. I have to check some more though...

No, the stator will not do anything to help the magnets become
stronger. An excited field alternator has brushes and slip rings so the
brushes can conduct a very small amount of direct current from the
battery (via the regulator). The DC goes in one slip ring, through the
rotor windings and out the other slip ring to ground.
The DC causes an electromagnetic field with *fixed polarity* in the
rotor. In other words, any pole on the rotor is always a north or south
pole, and this is true even when there is no current going through the
slip rings, because the poles have a small amount of residual
magnetism. The electromagnetic field in the rotating rotor passes
through the winding in the stator, inducing an alternating current in
the stator, because a north pole will pass the winding, then a south
pole will pass the winding and on and on as long as the rotor is
turning. So the AC current goes to the diodes in the rectifier and gets
changed into DC to charge the battery, and light the lights.

Now, as for the weak trigger magnet on your rotor, it just may be that
when you turn the ignition key on and off, and the nearest rotor poles
are energized and de-energized they produce a fairly strong
electromagnetic field, and that electromagnetic field could conceivably
cause the north and south poles in your trigger magnet to become
randomized...

OTOH, the trigger magnet might suffer from "refrigerator magnet
syndrome" if the magnet actually touches the steel parts of the rotor.
Refrigerator magnets will get weaker over the years, from being stuck
to the door of a refrigerator, but nobody complains about that, because
they don't ever try to take their refrigerator out on a Sunday Morning
Ride...

 

I wouldn't drill it out until I was really sure. It could also
be an electromagnet excited by an electric charge. If there's
another problem (maybe fixable) in the rotor you don't want to
take a drill to it.

Seems like you want to know whether the rotor's good or bad
otherwise and then whether it's a permamant or electromagent.

I really think you need to get on an owner's forum and ask
people who've worked on them before. Plan B would be to take
a look at another rotor that was in good working condition
and compare them.

 

I appreciate all the help. Unfortunately I can not be sure of any of
these part being the correct ones since I bought the bike at auction..


Does anyone happen to know what the gap between rotor and pick-up coil
is suppose to be??

Thanks again for the help

 

auction..

Like I said, I'd try to check out the rotor first.

Assuming it's a slip ring and brush design:

What resistance is there between the slip rings with brushes
isolated from the rotor ?

Is there +12 volts getting to the slip rings ?

I wouldn't worry about the hall trigger until I knew the answers
to these questions. If either of the above problems was present,
you'd be wasting your time fiddling with the trigger. After
I was pretty sure the rotor was OK otherwise, I'd worry about
whether I had a permanant or elctro magnet and what might be
wrong with it.

You also ought to get onto some of the 650 forums or email lists
to get a better idea of what you're dealing with. Lists and forums
of this type are really vital sources of tech info and leads to
spare parts.

Don't know if there's a Clymer or Haynes available, but if there is
I'd buy it too.