Sportster Magneto

[billpedalino]

I just completed rebuilding the magneto for my 1964 CH. I had the rotor re-magnetized, replaced all seals, bearings, cap, condensor, etc. The only original consumable parts that remains are the point assembly and the field coil, as they are original Faribanks Morse and they are in very good condition. My experience with the field coil is that if they check out with a continuity tester and if the secondary winding does have continuity to ground, then the unit is probably good, as they rarely go bad. Plese correct me if I'm wrong here.

I then bench-tested the unit to make sure that it sparks, and it does. I attached new spark plug wires and spark plugs and spun it by hand and it fired the plugs. All is right with the world.....

HOWEVER, I have become somewhat obsessed about magnetos. I severely damaged my knee after buying my first Sportster in the in the 1960's. We all know the scenario; worn kicker gears and bushings, low magneto spark, a strong right leg, little expereiece, and more balls than brains. 'If it doesn't start, kick it harder and faster'.... This injury as remained with me and at this age, I don't want to re-injure myself. Therefore, I have (incorrectly) installed the 1965 and later advance/retard plates.

My concern is this; in my memory of ancient times I seem to recall that when hand-testing the magnetos that I rebuilt, they were able to produce a very strong blue spark that was clearly visable in daylight. This unit produces a consistant spark, but it is light in color under flourescent lights. Turn the lights down and the spark appears blue. Also, when I open the spark plug gap from 0.015" to 0.025", the mag has no problem bridging that wider gap. With the cap removed and a grounded screw driver placed close to the field coil springs, the unit produced a spark, but again, it appears lighter (blue/white) than I recall. Also, with the screw driver place BETWEEN the springs the unit won't fire from both springs to the screw driver - the gap is apparently too wide. I seem to remember doing this double-spark check years ago, but I'm not sure. Also, this rebuilt unit is a little stiff to spin fast by hand with the re-magnetized rotor and the new seals. Finally, Just to rule out the field coil, I tried two other used coils that I have (one with the Faribanks impressons and one that appears to be aftermarket) and both yielded the same spark intensity.

Its my opinion that low-intensity output is probably the main reason why these magnetos are dis-favored by some and probably accounts for much of reason why some Sportsters start hard and why there were so many worn kicker gear bushing and rounded clutch hub tooth problems so common in older Sportsters. I just want to make sure that this problem is fully addressed now and that I have confidence in the magneto before I install it. But I would just hate to send it out to a magneto shop for needless testing if I'm just being over-concerned.

My guess is that my memory is wrong and that this unit is fine. However, I would appreciate input from guys that have remained more current with these magnetos than I.

Thanks,
Bill Pedalino

[rwm]

i base none of my opinions on fact. i think you want to test the magneto when it's hot( from an oven). and it is harder to make a spark under compression then on your work bench. but i would say put it in the bike and find someone younger to kick it first.

[brianbbs67]

I just completed rebuilding the magneto for my 1964 CH. I had the rotor re-magnetized, replaced all seals, bearings, cap, condensor, etc. The only original consumable parts that remains are the point assembly and the field coil, as they are original Faribanks Morse and they are in very good condition. My experience with the field coil is that if they check out with a continuity tester and if the secondary winding does have continuity to ground, then the unit is probably good, as they rarely go bad. Plese correct me if I'm wrong here.

I then bench-tested the unit to make sure that it sparks, and it does. I attached new spark plug wires and spark plugs and spun it by hand and it fired the plugs. All is right with the world.....

HOWEVER, I have become somewhat obsessed about magnetos. I severely damaged my knee after buying my first Sportster in the in the 1960's. We all know the scenario; worn kicker gears and bushings, low magneto spark, a strong right leg, little expereiece, and more balls than brains. 'If it doesn't start, kick it harder and faster'.... This injury as remained with me and at this age, I don't want to re-injure myself. Therefore, I have (incorrectly) installed the 1965 and later advance/retard plates.

My concern is this; in my memory of ancient times I seem to recall that when hand-testing the magnetos that I rebuilt, they were able to produce a very strong blue spark that was clearly visable in daylight. This unit produces a consistant spark, but it is light in color under flourescent lights. Turn the lights down and the spark appears blue. Also, when I open the spark plug gap from 0.015" to 0.025", the mag has no problem bridging that wider gap. With the cap removed and a grounded screw driver placed close to the field coil springs, the unit produced a spark, but again, it appears lighter (blue/white) than I recall. Also, with the screw driver place BETWEEN the springs the unit won't fire from both springs to the screw driver - the gap is apparently too wide. I seem to remember doing this double-spark check years ago, but I'm not sure. Also, this rebuilt unit is a little stiff to spin fast by hand with the re-magnetized rotor and the new seals. Finally, Just to rule out the field coil, I tried two other used coils that I have (one with the Faribanks impressons and one that appears to be aftermarket) and both yielded the same spark intensity.

Its my opinion that low-intensity output is probably the main reason why these magnetos are dis-favored by some and probably accounts for much of reason why some Sportsters start hard and why there were so many worn kicker gear bushing and rounded clutch hub tooth problems so common in older Sportsters. I just want to make sure that this problem is fully addressed now and that I have confidence in the magneto before I install it. But I would just hate to send it out to a magneto shop for needless testing if I'm just being over-concerned.

My guess is that my memory is wrong and that this unit is fine. However, I would appreciate input from guys that have remained more current with these magnetos than I.

Thanks,
Bill Pedalino

A well setup magneto should jump 1/4" with blue/white spark very intense. You can make a simple jig to test.

Set it and kick. Remember to hold that pedal or it will come back. If worried about coil check ohms/continuity between points wire and laminated bar. Should be none. Also if this does not work change the point and condenser, they are the most common prob.

[billpedalino]

Thanks for the replies. The contunuity between the point wire which is the primary winding and the laminated, grounded lugs which are common to the secondary winding is zero (infinate ohms), so I guess the coil is ok. Because the motor is on the bench and won't be installed in the bike for quite some time, kicking it isn't an option at this point. But I will set up a jig with some spark plug wires and see if it consistantly jumps the 1/4" gap when spinning it by hand.

I havent changed the points, as they look very good, but if the 1/4" gap is a problem, I'll try that as well. The condensor is new, but its not the long one that used to come with the Faribanks Mag. - its from Ted. Without the equipment to check the microfarrads, is there a way to check condensors?

Thanks

[brianbbs67]

No good bench test without what you mentioned. The best test is to swap condenser and see if you have different results. And of course everything else has to be right to get a true result. Improper gap, wires, coil connection with magnet, dust debris. And if your finding your going thru condensers on a regular basis, it's probably because it's pushing the spark to hard due to any of the aforementioned items. When it's right, it's great, a little off not so much. But just remember almost all lawn mowers and outboard motors run off magnetos! So it's simple yet not!

[TimR]

Bill, A disadvantage of a magneto is they some times take more out of a motor HP wise than they return. A magneto's spark is proportional to it rotational speed. Kicking produces a low spark but as you increase RPM the spark gets hotter. To prove this prior to installing it on the motor put the drive gear against either a spinning wire wheel or buffing wheel, let it wind up. Just stay clear of the spark. That dog will BITE YOU! Things also fire differently under compression, there is a reason spark plug testers have a compressor hose attached.

[billpedalino]

Tim,
I'm aware that the spark intensity increases with rpm. The faster the magnetic flux lines are cut, the more intense the impulse to the field coil. That is the essence of my concern with Sportster magnetos. I'm a firm believer that many hard-starting Sportsters do not suffer this problem due to their DC Linkert or Tillitson carburators, as many believe (I'm a big fan of both carbs). As you stated, the lowest output occurs at kicking speed. My experience is that when all else is right, a properly tuned and charged magneto goes a long way in addressing hard starting problems. That's why I'm probably reading more into the spark quality of (what is most likely) a properly rebuilt magneto for my '64. Looks like I'll stop guessing about spark color and gap distance and just send the unit to Morris in N.J. to have the output properly checked. They're not cheap, but they do an excellemt job.