Lets talk magnetos.

Status
Not open for further replies.
acotrel said:
Perhaps heat kills the condenser or stuffs the internal wiring and the magnets get the blame ? I once dropped my bike on the road and the magneto died. I used a rotating magnet magneto on a race bike for 12 years and never had a problem, even though the motor was enclosed within a fairing. Of course that is not the situation you get with a touring bike in desert conditions.
Click to expand...

shellac melts in magnetos that overheat , now whether that renders the condenser or armature wiring inoperative or both , this was a common complaint about magnetos.. the idea that magnets fail through heat seems to me unlikely, just how hot are these engines running? And there are downsides to magnetos that are not mentioned.. the taper on the chain sprocket is known to slip... serious rain or road flood is likely to short them out.Do they really give a better spark than a modern digital coil and EI ? And as for that cumbersome auto advance device , no . All brit
bikes back in the magneto day offered manual AR on their top of the range models (Triumph may have been an exception) for which the punter had to pay a premium..Possibly for a big single pulling a sidecar up a hill then the option of retarding the ignition could be a godsend, but otherwise can see little point or advantage except for period correctness.. Yet Ron Wood fitted them and one has to respect that
 
From my short email exchange with the owner of BH-T magnetos says they now have an electronic advance curve implemented using the Hall effect to trigger. No voltage from a battery source needed. This sounds very good and answers a lot of questions raised on this forum. Mag fits just like old Lucas mag. What remains is an unbiased test.
 
"How hot does a Norton motor get?"

Barrel temp -400F is common near the top rear of the barrel at normal highway speed. [70 to 80mph]

Case temp -300F is easily reached after some time at highway speed. 375F after a spirited ride up a mountain pass in the summer. [highway 50 in the middle of Utah]
Measured using a sensor near the top rear of the RH case.

Head temp -375F is common. I have seen just under 600F pulling 2 people up a long pass in Wyoming. As soon as I noticed my pyro reading I backed out of the throttle and crossed my fingers. It lived.

It is very likely that a Mag is going to see more heat on a Commando than on an Atlas. Due to the forward rotation of the motor, air from the barrels is likely to pass all around the rear mounted mag. Both failures I was involved in were on Commandos.

One of them [my bike] would start if it was coasted fast enough to spin the motor pretty fast. That was not tried on the other bike. Both worked again after the magnets were replaced. Jim
 
BH-T said they are now using magnets with far greater resistance to heat ( which recognizes a problem did exist). Still, I can see the need for an unbiased test. Done right, an air scoop would work and would guard against heat directly off the engine. But the potential to just look ugly would be great. There's a design problem for you.
 
Don’t the new BTH ‘magnetos’ use external coils?

If so, are they actually magnetos? Or are they a self generating electronic ignition system?
 
comnoz said:
"How hot does a Norton motor get?"

Barrel temp -400F is common near the top rear of the barrel at normal highway speed. [70 to 80mph]

Case temp -300F is easily reached after some time at highway speed. 375F after a spirited ride up a mountain pass in the summer. [highway 50 in the middle of Utah]
Measured using a sensor near the top rear of the RH case.

Head temp -375F is common. I have seen just under 600F pulling 2 people up a long pass in Wyoming. As soon as I noticed my pyro reading I backed out of the throttle and crossed my fingers. It lived.

It is very likely that a Mag is going to see more heat on a Commando than on an Atlas. Due to the forward rotation of the motor, air from the barrels is likely to pass all around the rear mounted mag. Both failures I was involved in were on Commandos.

One of them [my bike] would start if it was coasted fast enough to spin the motor pretty fast. That was not tried on the other bike. Both worked again after the magnets were replaced. Jim
Click to expand...
 
Jim magnets cannot be what they used to be... can remember the timing slipping on the ES2 and a serious overheat.. the pipe glowed cherry red almost to the silencer.. but the mag kept working and it itis of course under the dyno and closer to the cylinder so less air circulating . Years later it has begun to show classic signs of impending failure... erratic cold starting and no hot starting. Will post what the reconditioners find usually though this is a sign of condensor failure. But thanks for posting the barrel temps , much higher than i would have expected -the next time mine is off will investigate enlarging the casting holes between the cylinders.
 
I tried a Lucas K2 mag on an Atlas bottom end years ago in the SS clone when it was a Fastback. Could never get the timing right on both cylinders at once, apparently due to a bent shaft. Each cylinder had to be set a couple degrees either side of 32 btdc. Gave up and went back to a standard crankcase and a Boyer.
 
Danno said:
Could never get the timing right on both cylinders at once, apparently due to a bent shaft. Each cylinder had to be set a couple degrees either side of 32 btdc. Gave up and went back to a standard crankcase and a Boyer.
Click to expand...

This was a common fault on the K2F magnetos, and was due to either poor machining of the cam rings, or the cam rings were improperly centered in the housing. It was easily corrected by a new CNC machined cam ring, or by shimming the cam ring to center. The procedure has been explained elsewhere on this Forum.

My Atlas fires within 1/2 degree, and after correcting the firing mismatch, previously 6 degrees, the vibration is noticely less.

Slick
 
oldmikew said:
Jim magnets cannot be what they used to be... can remember the timing slipping on the ES2 and a serious overheat.. the pipe glowed cherry red almost to the silencer.. but the mag kept working and it itis of course under the dyno and closer to the cylinder so less air circulating . Years later it has begun to show classic signs of impending failure... erratic cold starting and no hot starting. Will post what the reconditioners find usually though this is a sign of condensor failure. But thanks for posting the barrel temps , much higher than i would have expected -the next time mine is off will investigate enlarging the casting holes between the cylinders.
Click to expand...

Copied from coolmagnetman.com

Concerning NdFeb "rare earth magnets" The most powerful magnets around. Used in some newer magnetos because they make a big hot spark at low speed.
There are definitely other types of magnets available that easily handle the temps but they are not nearly as powerful.

"Neodymium-Iron-Boron Magnets

Lets talk magnetos.


NdFeB magnets are the strongest permanent magnets around today, and are not very expensive. They are used in headphones, disk drives, new toys, all over the place.

a. Mechanical Shock
These magnets are brittle - they will chip or crack or break easily when:
dropped onto a hard surface
allowed to smash together with another magnet
allowed to smash together with a piece of metal
struck with a hammer or other hard substance

So again, handle gently, like you do with your iPod or cell phone. When you bring two magnets together, be prepared to have the force of attraction increase quickly and dramatically as the North pole of one gets closer to the South pole of the other. Better still, place a plastic disk or rubber washer between them so there is a cushion between them. Watch your fingers so they don't get pinched! Because these magnets are so much stronger than others, this needs to be a real precaution!

You may not realize it, but every particle within a magnet wants to push away from every other particle next to it. Yes, it is attracted to the particle at its North end and South end, but all along its sides, there is a repulsion. Because of this, if two magnets are allowed to smash together, expect a small chip or particle to fly away at a high velocity and can fly into your eye. That is why it's a good thing to wear goggles - protect your eyes from the unexpected. Those particles have sharp edges and will easily scratch your eyes.

b. Heat
This is the weakness of this magnet.

Their maximum working temperature is only 150 degrees C (302 degrees F).
The Curie Temperature for NdFeB magnets is 310C (590F).

This is why they usually aren't used in motors. Keep your magnets cool. "
 
From my experience - Engine heat is not the problem with Joe Hunt magnetos. I've run my Atlas in 110 deg Fresno summer heat for years. If engine heat was the problem then I would know it for sure. I've never had neo magnets lose their power on a mag.

The common problem is users who don't gap the plugs to a max of .018" Plugs come gaped at about .025" and that can burn up a mag coil. Each mag comes with instructions to gap the plugs. The points should be gaped around .012"

When JH mag tried bigger neo magnets (early 2011) the electrical heat could actually melt the plastic points arm or fry the coil after a couple minutes - even when bench testing where the mag body doesn't heat up. Never use non resistor plugs or plug caps, use solid copper wires only. Most people just throw in new plugs and never follow the instructions and some ruin the coils this way. Its the electrical heat generated by a mag that can burn out a coil. Mags spark way hotter conventional setups so they have to be set up right.
 
Last edited:
Tune up kits from JH comes with new points, condenser and new plug leads, on my old Triumph JH maggie I used vintage copper leads for the old vintage cars I had a big roll of it and made them up, yes the 18thu set for the plugs is very important, my Champions plugs also gets long life out of them they run very clean and don't burn out, I have had no problems with the condenser on both maggies, the tune up kit is very cheap for about $35 but if you don't use a file on the points they will last a very long time.

Ashley
 
texasSlick said:
This was a common fault on the K2F magnetos, and was due to either poor machining of the cam rings, or the cam rings were improperly centered in the housing. It was easily corrected by a new CNC machined cam ring, or by shimming the cam ring to center. The procedure has been explained elsewhere on this Forum.

My Atlas fires within 1/2 degree, and after correcting the firing mismatch, previously 6 degrees, the vibration is noticely less.

Slick
Click to expand...

This was about 40 years ago. I checked into getting it rebuilt and the cost was exorbitant. Had I known there was an easy fix at the time....
 
Status
Not open for further replies.
Back
Top