Overhauling a Megger magneto.

[Mike Phelan]

This is based on the one I have and I thought it would be more useful to give this approach, rather than a “Success Story” type scenario.
At first glance, it was working; the problems were really just that the terminal buttons were sticking a bit and the magneto handle was a bit devoid of lubrication.

I opened it up, taking the two terminal buttons out with their springs and saw that the brass blocks and square housings just needed cleaning to cure them sticking.
I unsoldered the three leads from the movement and removed the two screws holding it in; they are brass and have a spring washer and a flat washer; these latter are the biggest ones; take note as some more washers will be removed later. Put the movement somewhere safe and away from ferrous items.

The complete magneto and gearbox can be taken out then – three more screws, noting the washers and which way round the clamp is.

As it all needed lubricating, a complete dismantling was on the cards. The intermediate gear can be left in to avoid having the punch out the pin, but everything else can be stripped.
The screw on the handle shaft is a left hand thread – also note any shims on this item.
The rubber washer might have perished – part of an old inner tube would be a good replacement.
Be careful with the actual magneto; it has brushes and slip rings and each end of the spindle has needle rollers – watch out . There should be 22 on the pinion end, 18 on the other end.
I left the armature in the magnet to avoid lessening the flux (I have worked on many car magnetos!); it is easy to clean the pivots and slip rings in situ.
The handle and intermediate spindles have oil wicks in them retained by a bronze spring held in with a screw. The handle one will push out, but you need to fish the other one out with a pin.

Remove the brushes from the magneto and clean them and the holders.
Wash everything in IPA except the magnet and armature. If you squirt IPA down the wick hole in the intermediate spindle and spin it, it will clean the bearing.

Refit the handle, oiling the ball and spindle – replace the cleaned wicks after soaking them in oil.

Now for the needle rollers – the 18 on the slip ring end can be fitted individually after entering the end casing into the armature spindle, and the cover (2 screws) replaced.
Grease the spindle and drip some oil down the rollers before you put the cover on.

The ones at the pinion end are a different matter! They run in a track on the spindle and need to be kept in place as the complete armature and magnet are fitted to the end casing. Looks like a daunting prospect, but is quite easy if you go about it in the right way (having overhauled a few car gearboxes proved useful).

Get some masking tape, or even Sellotape. About 1” or ½” wide. Cut off a couple of pieces 2” long, put one sticky side up. on the bench, then stick the other on top of it, with half of the width of the long side showing, the other half stuck to the bench. Then put 22 of the rollers close together on the adhesive upper surface, leaving half of their lengths free of the tape. See picture (1).

Cut the edge of the tape with a Stanley knife as shown so the piece with the rollers is free from the bench. Then, after greasing the track on the spindle, carefully wrap the tape with rollers on the track (2). They are safe now!

This leaves half of the rollers exposed. Wrap a few turns of wire around them (3) so the tape can be carefully removed. Now, with extreme care, enter the spindle so the rollers go part way into the outer race, and pull the wire out. Job done – screw the two long screws back into the magneto, reassemble and test. Allow a drop of oil to run into the roller race on the pinion end and some grease on the gears.