Flywheel magnets losing strength, any experience out there?

[John Orchard]

A friend of mine is having trouble getting his bike started, it's a modern bike but it raises a technical issue that could apply to old vintage bikes.

The bike in question has very weak intermittent spark, all electrical components have been tested and/or replaced, what he has noticed is that removing the stator use to be very difficult due to the magnetic pull, but now there does not seem to be much pull from the magnets.

I Googled the matter, seems that high temps or strong impacts can reduce a magnets power.

In 45 years of working on bikes I have never come across this myself, I'm interested if anyone else has?

[justanothercgrader]

No, not on a flywheel, although recently i had to replace the base on my magnetic dial indicator had lost its strength after 30 odd years.

[Mick D]

Yes all rotors lose magnetic strength. especially ones from cooked engines. Heat is the enemy of Magnetism.
Compare identical new one to an old one by seeing seeing how many nails they pick up at room temperature.
Boil them in water and then see how many nails they pick up,,, about none, i think?

 
  I have always believed that when out trail riding and a bike fails from low spark, difficulty to restart after stalling when Hot.

Put it in the shade. Open the ignition cover if possible. Take a break. Let everything cool down.
Clutch it down a big hill and go home 

And about cooling ignitions? we all want reliability out on a trail ride.
Water?, Heat, cyclic heat are the enemies for both rotor and stator.
Husky WR360's suffer ignitions destructed from heat as do many bikes.
I am about to repossess WR360 very soon.
My intention is to add a small plastic fan impeller like those little ones fitted on to the back of most washing machine pump motors.
https://www.google.com.au/search?q=fan+impeller+types&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiOitWZourWAhWFVLwKHTSqCzkQ_AUICigB&biw=1094&bih=474#imgrc=FBOeYoXcPAIyrM:

Trim it to a minimum, so that the cover only has to be spaced out a minimum.
Lightweight filtered feed hose in from the top front of bike(backbone), Holes in impeller machined and placed over slots in external rotor, forcing cool intake air to have no choice than to be drawn through and over Stator. before being pumped through a lightweight exit tube to rear subframe area etc.

I think Cool ignitions go hand in hand with improved reliability as well as long jeopardy.
Weeeell that's my plan at least.   

[HVA61]

An important part of the relationship between magnets and temperature is the fact that heating the magnet causes its molecules to become more out of order or for the want of a better term disorderly. Basically magnets are dipoles, which means they have an opposite charge, or magnetic direction, at each end. This is a result of most of the magnetic molecules facing the same direction. When magnets are heated, those polar molecules all start moving around. The average direction of the entire magnet’s polarity becomes a little bit disorderly because those magnetic molecules are no longer facing the same direction. So basically as Mick described a cool magnet is much more effective than a hot magnet.  In most cases if you significantly overheat a magnet the magnet will lose its total effect.

[Mick D]

I always wondered why from a technical point of view, thanks Rob

[HVA61]

your welcome

[LWC82PE]

Yes they can loose magnetism. You can sometimes get them re-magnetized. I have had old Villiers flywheels done. Flywheels should not be stored loose for a long period of time. Try and keep the stator in them or fit keepers to them. Often when i have bought new rotors and flywheels they come with steel keepers attached to them.

[fred99999au]

https://www.youtube.com/watch?v=QnkAEhaxK9I

[Lozza]

A friend of mine is having trouble getting his bike started, it's a modern bike but it raises a technical issue that could apply to old vintage bikes.

The bike in question has very weak intermittent spark, all electrical components have been tested and/or replaced, what he has noticed is that removing the stator use to be very difficult due to the magnetic pull, but now there does not seem to be much pull from the magnets.

I Googled the matter, seems that high temps or strong impacts can reduce a magnets power.

In 45 years of working on bikes I have never come across this myself, I'm interested if anyone else has?

If the stator still produced the correct amount of voltage it should still work. My experience heat will wreck the stator long  before  the magnets loose their strength. Being modern I assume its a DC stator?

[grouty]

The biggest issue I have had, is the built up heat has no where to go. There is no connection between the hot ignition/flywheel and the outside world (i.e. the ignition outer cover). I have had a few friends that have sealed the cover, fitted a small breather in the top with a pipe that runs up under the tank and then put some thin oil in to fill it to about 1/4 to 1/3 full. This allows the heated oil to make contact with the cool side cover. They have never had an issue with a hot ignition.

[TT5 Matt]

What's a DC stator?I'm sure they all produce AC power,low volts for magnito/charging and lighting systems and high volts for cdi ignition systems which seem to have the most dramas on bikes

[Lozza]

Modern efi bikes have DC stators , stator is smaller and eliminates the rec/reg. Magneto has to have rec/reg to convert AC to DC

[HeavenVMX]

A rotating electrical machine can not produce DC directly. All rotating machines produce AC and it is converted to DC via either a solid state rectifier or a mechanical commutator. The very nature of a rotating permanent magnetic machine makes direct production of DC impossible as the coils or windings passing both north and south poles of the magnet which is unavoidable. The frequency of the AC is dictated by number of poles and speed. The modern stators must contain the rectifier internally.

[Hoony]

yes this is mainly true with some exceptions.

 if the stator is a permanent magnet (or excited by a dc field winding) and the rotor has a commutator
then you do get dc generated directly (like a Tachometer, DC Generator) in the case of a tachometer the voltage is directly proportional to the speed in RPM.

[Lozza]

A rotating electrical machine can not produce DC directly. All rotating machines produce AC and it is converted to DC via either a solid state rectifier or a mechanical commutator. The very nature of a rotating permanent magnetic machine makes direct production of DC impossible as the coils or windings passing both north and south poles of the magnet which is unavoidable. The frequency of the AC is dictated by number of poles and speed. The modern stators must contain the rectifier internally.

When you hold a modern DC stator in your hand the rec/reg must be microscopic. On KTMs  around 2010 the stators change from 8 pole to 12 pole like this but the wiring certainly has no rec/reg. Trailtech seem to think they have DC stators ?
http://www.trailtech.net/stators-flywheels/ktm-stator-kits/s-8362-05