Poor starting on new Amal and BTH Magneto

[clevtrev]

I suspect much of that damage to your insulation was due to the ravages of ozone, not the ravages of time, but I decided to do a quick experiment that sheds some light on this.

In case you haven't experienced it, if you happen to find a rubber band on top of a shelf or filing cabinet close to a fluorescent light it will be quite brittle, which I assume is due to the UV light from the bulb. I mention this because my experiment used a rubber band as well as special type of light bulb that emits a lot of UV. However, unlike a fluorescent bulb, this one also emits the distinct smell of ozone. In my experiment I shielded the rubber band from the UV so it was exposed only to the ozone.

I meant to check a few times along the way, but got busy and left it for ~24 hours. When I checked this morning the rubber band was like a rock. Although this was an "uncontrolled experiment," in that I didn't measure the ozone concentration, it nicely shows why you don't want electrical components near ozone.

The insulation in the carriage has gone the same way,no motor in there !

 

[Magnetoman]

The insulation in the carriage has gone the same way,no motor in there !

Not unlike the case of old people, all of whom have wrinkled skin. However, much more so on those who tanned for hours on the beach in their youth.

 

[clevtrev]

Not unlike the case of old people, all of whom have wrinkled skin. However, much more so on those who tanned for hours on the beach in their youth.

At what age does this start ?

 

[Magnetoman]

At what age does this start ?

It starts at birth. But, simply knowing what 'SPF40' means can keep the process from accelerating. Botox and mechanical rebuilds can even reverse it. But, sometimes the latter can be like some motorcycle restorations. Some of those are "10 foot restorations," i.e. they look great as long as you don't get too close.

 

[redbloke1956]

Not quite true. It also will need remagnetizing after the armature has been removed to install the seal. It still will work afterwards, but with significantly reduced output.

As to the question someone asked (which I must have missed when it was asked, and a quick search didn't turn it up), i.e. Can a Comet run sweetly with a compact Lucas mag or not?, the answer is 'yes'. However, the mag is 60 years old, so it shouldn't be surprising it needs refurbishing at this point to return it to full health. If I were to rebuild someone's Comet magneto (which I won't do, because I don't do it as a business), I would have no qualms at all about offering a double their money back guarantee against failure for 10,000 miles if no maintenance were performed. If they did just a trivial amount of maintenance at a few points along the way (regrease the cam, measure/adjust the points, inspect and clean carbon from the slip ring) I would increase the length of the warranty. The Lucas magneto is a fundamentally sound design, and is completely capable of providing someone with years of trouble free service after rebuilding before it needs any additional maintenance.

Unfortunately, there are too many magneto rebuilders, some of whom are quite well known and commonly recommended, who use incorrect components and incorrect equipment to remagnetize them (if they remagnetize them at all). I address at length what to look for when searching for someone to correctly rebuild your magneto with proper components at:

http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=464907#Post464907

Hi , Magnetoman, I just saw this post, I was under the impression that, similar to a Generator or Alternator, the slip ring on a mag should have a Patina to maintain lubrication between brush and slip ring and also for a low resistance path for current flow? When you say that you clean the slip ring, can I ask ....to what extent? Do you remove the Patina?

regards
kevin

 

[Magnetoman]

Hi , Magnetoman, I just saw this post, I was under the impression that, similar to a Generator or Alternator, the slip ring on a mag should have a Patina to maintain lubrication between brush and slip ring and also for a low resistance path for current flow? When you say that you clean the slip ring, can I ask ....to what extent? Do you remove the Patina?

Low resistance of the carbon/brass contact isn't too much of an issue because if the voltage is enough to overcome the resistance of the air in the 0.018" gap of the spark plug, it won't have much of a problem with the resistance at that interface. However, a patina is an oxide film, so ideally it would be a shiny unoxidized brass surface. But, all I do to clean a slip ring is to use a piece of cloth to remove any build up of carbon dust. Unless there is wear, in which case I also turn it in the lathe. That certainly removes all patina. Lubrication isn't an issue, because the graphite in the brush is self-lubricating.

 

[redbloke1956]

Low resistance of the carbon/brass contact isn't too much of an issue because if the voltage is enough to overcome the resistance of the air in the 0.018" gap of the spark plug, it won't have much of a problem with the resistance at that interface. However, a patina is an oxide film, so ideally it would be a shiny unoxidized brass surface. But, all I do to clean a slip ring is to use a piece of cloth to remove any build up of carbon dust. Unless there is wear, in which case I also turn it in the lathe. That certainly removes all patina. Lubrication isn't an issue, because the graphite in the brush is self-lubricating.

Thanks for the reply mate, Yeah OK that makes sense, but on gens, motors and alternators the patina is the grey/black film created by the carbon/graphite in the brushes and is essential for brush life and efficient operation, on all machines I have worked on if the patina was disturbed or removed (by skimming in lathe) we spent considerable time bedding the brushes and ensuring an even patina before putting them back into service. So while I agree about the miniscule voltage drop experienced in the magneto I am not so sure about the lubrication aspect as I have seen many brushes wear out rapidly due to not spending the time to produce the initial patina.........Now as I have said this all applies to the slip rings and commutators in motors and gens but I still don't see why the same wouldn't apply to a mag........thoughts?? Kevin

 

[Magnetoman]

Now as I have said this all applies to the slip rings and commutators in motors and gens but I still don't see why the same wouldn't apply to a mag........thoughts?? Kevin

If you take a look at the following you will see the results of measurements I made on the hardness of brushes:

http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=456910#Post456910

The difference between a brush for a magneto slip ring and one in a generator is the latter runs only against metal as well as carries carries a lot of current. Until the rubbing surface of a generator brush is formed to an arc of the same radius as the commutator it makes only partial contact and thus all the current flows through only a small portion of the brush. In the extreme case of a flat brush it would makee contact only along a line rather than over its entire surface. So much current flowing through a small area can "burn" the brush.

 

[Tug Wilson]

Agree with Craig on procedure although I lightly tickle and use virtually no throttle until firing and definitely no choke. This is with original old Amal remote float carb. All settings as per book. 2 or 3 kicks when cold required only 1 when warm, again no throttle. Engine rebuilt including standard mag.

Were you to operate the choke closed the engine should literally choke!

Not much help to Minivin unfortunately. Good luck.