henry mag 1 new verbage 2014 r2One guy tells me that magnetos are great, another tells me magnetos suck. Who is correct?


They both are! Magnetos of the past were always known for performance, particularly in the high rpm range, and for use without a battery needed, as they are independent ignitions. Problem is starting was often an issue. Add to that, the original manufacturer’s cast parts went downhill over the years, since as time went by tooling became more and more worn.


I’ve heard old magneto brands were all the same. True?


Sort of. Back then, all manufacturers of magnetos for two-cylinder motorcycles, including Harley-Davidson themselves, used Fairbanks-Morse magneto heads. From the start, all our magneto mount systems could be retarded for starting, while others would ‘kick back’. As per the mag head, here at Morris Magneto, when we received a skid of magneto heads from Fairbanks-Morse, we would return about one third of them as substandard. They would simply ship them to someone else.


So are they reliable?


The physics is very basic, simple and foolproof. Magnetism flowing through a coil of wire, making an electrical charge and spark. The least energy needed to make said spark, an efficient ‘direct drive’ fire.


1969 xlch - Last stock Magneto
1969 xlch – Last stock Magneto

Tell me more about this ‘kick back’.


When we started, all other manufacturers were making fix-timing (non-retardable) magnetos (Harley had gotten away from them, since DOT and NHSB began requiring batteries). This meant that when you went to start the bike, the spark often turned the engine backwards instead of starting. The kick arm would ‘kick you back’, sometimes wiping out knees and ankles. So our efforts covered half the starting issues.


So what is the other starting issue?


The direct-spark aspect of a magneto means that the faster it turns, the hotter the spark. But that also means the slower it turns the colder the spark. So the motorcycle had to be kicked fast enough to at least jump the spark plug gap, or else it could not start the engine. In the early ’80s, we took the technology of an impulse coupling, and adapted it to motorcycle magnetos. This meant that no matter how slow the engine was turned, you still got an extremely hot spark. This is our series of magnetos known as M5, G5, H5, T5, and F5.


But I still need to kick, right?


To run the motorcycle without a battery, yes, albeit not as hard as you had to with the older mags, especially with our -5 type impulse mags. Also, if you had an electric start, the impulse magneto means that an electric start can be used without destroying the starter, regardless of how big the motor is.


Is that the “clicking” type magneto I’ve heard of?


Yes. Each time the motor turns over, a pawl-arm stops the magneto, winding up a spring. When the engine reaches proper retarded timing for starting, the pawl lets go, and the magneto clicks. Once the engine starts, the pawl is retracted automatically, running the magneto advanced. When the engine is shut off, a click or two can also be heard.


But doesn’t running advance makes the engine ‘ping’?


Unlike battery-coil ignitions, the direct spark coming from a magneto is very resistant to ping issues.


Billet Magneto Shown here with optional faux cast finish

But you were still using these Fairbanks-Morse magneto heads…


As frustration with the quality grew, we decided to make our own billet aluminum mag head housings. Since we were a vendor for Fairbanks-Morse (we machining parts for them), we had access to blueprints, which meant we could make them correctly. We also recognized the need for a stronger magnetic rotor, so we began using Rare Earth magnets (about twice as strong by volume). We modeled and built over 100 variations, settling on a unique bulletproof design that took the same torque to turn as the old Alnico magnet type (more on this to be posted elsewhere).


So how hot are these new magnetos with the rare-earth rotors?


We’ve actually built magnetos capable of jumping over ¾ of an inch at only 350 RPM. In fact, the -5 impulse models will do it at virtually zero RPM… now that’s hot!


Leave a Reply