Magneto Bearings

[LJ.]

I have been noticeing a lumpy running bike just recently and have mentioned about the points spring in another thread but it seems problems have been persisting. So a quick look at the points and finding the rotation is very offset (very slack with a lot of side play) which made me wonder if the bearings were ok. Here is what I found last night after a strip down of the maggie...

Inside it was all gungy, washed all parts except the armature, in degreaser, and found that the bearing is of a metric size and not a tight fit, there being one millimeter play. I dont know who rewound the armature (anyone recognise?) but it has been no problem in the last 8 years since it was done, but the bearing was a bit of a bodge! Has anyone else had this problem and does anyone know where I can get a new bearing to fit? (In UK)

 

[Caretaker]

Hi LJ, SRM or magneto.co.uk and suppose many more have the bearings. Do I get it right, the inner center of the bearings are loose on the armature? Then you need new bearings indeed! Side to side or lateral play is no good, you easily end up with an "RVT" mag, (the model with Random Variable Timing)


Regards
Erling

[trevinoz]

Bearings should be readily available at bearing suppliers. In australia the ones I have been getting are Japanese made. Number is E with shaft diameter. e.g. E12, E15. When fitting they must be shimmed to take out excess play in final assembly. Very time consuming.

[LJ.]

To my suprise after another posting on some other forum. It seems that I have the correct bearing and the reason as to why it is slack is that I should also insert a paper bearing insulation cup seen here at the foot of the page. http://www.magneto.co.uk/acatalog/Index.html So... I would imagine that as the slack is only half a millimeter the paper when loctited in would make the bearing a firm fit!

Erling... the inner centre on the armature shaft is a perfect fit it is the outer race cup that is slack...only by half a mil and as mentioned a few lines up, the paper insulater would take up the slack!

The next job is to try and make up my own insulater. Will let you know how it goes! 8) Fantastic! problem almost solved!

[Caretaker]

Hi, I've made bearing insulators with various materials, good luck. And as trevinoz writes, it must be shimmed to get the correct end play. If I understand it right, if the armature is too tight you wear out the bearings, too loose you get end play & side movement.

BTW, anybody know if it's possible to fit a steel plate CB assembly (see pic) to a K2F with a brass plate?

Thanks

Erling

[BrianDallasTX]

Great magneto site.  thanks for the link.  The A10 is my first bike with a mag. system so I am still on the learning curve.  Easy to figure out so far.

[LJ.]

Conclusion.

Well its been a learning curve over the last couple of days, the A10s magneto is now back together again and refitted to the bike engine. The timing was all set and to my suprise it was very simple. The reccomended BTDC measurement of 11.32 inch which was about 8 and a half millimeters was meaured out on a welding rod inserted into the cylinder. The rod was easy to pencil mark and read out against the joint between the cylinderhead and rocker cover for acuratecy. (sorry about spelling!)

I must admit that I now have all the more admiration for the old bike as it has been fun and well within the capabilities of a Do-it-yourselfer without any mechanical, engineering experience.

Also I have come to relise that the various information available does not always mention everything. for example, nowhere have I seen mentioned about the insulating bearing cup that seems vital for ensuring a good spark. It does seem that we cannot do without the various forums.

I now need to take it out for a blast in the morning to see if she is happy with the timeing settings. Wonder what the next thing will be? :)

[Caretaker]

Good work, hope it runs smooth & well!

You find reference to the insulation washer, shimming etc in the Lucas service manual. Mag is here: http://www.a7a10.net/manual54/magneto.pdf

Regards
E.

[LJ.]

Ha! Thanks Erling, howcome I always find the info on paper *after* the job is done? The bottom picture says it all...

No run out today... chucking it down with rain out there!

[fido]

BTW, anybody know if it's possible to fit a steel plate CB assembly (see pic) to a K2F with a brass plate?

Thanks

Erling

You can fit the steel plate complete with points as I did the opposite on mine. The brass one has a carbon brush which is supposed to ensure a good contact with the brass part of the armature even if the taper seating is not providing an adequate contact. The brass type are more fiddly for points adjustment but are generally regarded as a superior device.

[LJ.]

I too remember seeing something mentioned about the brass points plate being of a much better effort. I cant understand why you, Erling, would want to convert to steel. Unless it is for the ease of re-setting the points.

I found yesterday while the magneto was out and on my work bench just how easy it is to reset the points when they are angled directly facing me, much better than opposed to being on the bike. I suppose that if all the ignition system is perfectly set then adjustments would only come round when a complete overhaul is due. IE. greasing bearings, checking brushes and generally cleaning out the inners etc.

[Caretaker]

Thanks for the good information regarding points plate. I have always wondered if the steel plate was interchangeable, & if I do not get good hold of good points for the brass plate I may try steel, + my brass plate may not be in the best possible condition. But I do like brass in all shapes and forms 

Regards
Erling

[trevinoz]

While you are playing with your magy you should check that points open at same point on each cylinder. It's a fiddly job but worth the effort. Any variation can be fixed with judicious use of a grinding stone on the offending cam.

[LJ.]

Thanks Trev... thats something I did do and it appears that, luckily both cams are true, the points open exactly the same on both sides of the ring. It seems that even a new cam ring can be purchased if one is off set. Dont think I'd want to fiddle about trying to grind them the same.

By the way... I got out this afternoon and the bike runs fine! Might be just a tad improvement on timing from when it was last done, It certainly feels good to have done the overhaul myself.