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Magneto Bearing Extractor

by Doug Kephart

The little tool shown in the accompanying illustration is very handy to remove, without damage, the inner races of magneto bearings. The extractor itself is a simple turning exercise in the lathe. No dimensions are given, as the design can be scaled to suit the application and material at hand.

Douglas motorcycle magneto bearing extractor

However a brief description on construction and use should clarify the sketch. Select a piece of round bar larger than the race, the length of which is determined by the maximum depth the extractor will be used at (typically the drive end of the magneto armature.)

The bulk of the material is drilled out, but the rest will have to be bored out with a hooked boring bar, as a lip protruding into the inner diameter is required at the muzzle. The wall thickness should end up reasonably thin, say a 1/16", as it will need to flex. The protruding lip can be free-formed by hand in the lathe, as its exact contour is not critical. Indeed it does not even need to be rounded, as long as it can nestle in the bearing ball groove of the race. The other end is drilled and taped for the extractor bolt. To finish, slit the tubular portion with three or four evenly spaced hacksaw cuts. What you are making is a collet.

To use, spring the lip over the race. Tighten a worm drive hose clamp over the muzzle of the collet so that it can not expand and spring back off. Now all you need do is wind in the extractor bolt to push the armature shaft out of the center of the bearing race. Remember to protect the end of the shaft with a soft coin or similar so as not to damage it by the extractor bolt. The collet so applied has a very powerful grip. It is certainly better than prying on the race, trying to lever it off; which is impossible for the one pressed up against the fragile magneto slip ring.

© 2002 D. Kephart



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