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Magneto dismantle

Submitted by george_phillips on Tue, 31/01/2017
Forums
Electrical
Hi all - major problem. The alloy casing of the Lucas Magdyno has always had a crack at 2.0 o'clock when viewed from the timing side. As the bike is now stripped down I thought I'd fit a new casing (which I already had). To remove the magneto the good book recommends the use of a "U-shaped sprag" which fits into a hole behind the gear centre assembly and the screw hole at the top of the casing. So far so good but the upper part of the housing has sheared off so any ideas how to release to centre nut? I've tried making my own "sprag" but it simply bends. Very grateful for any ideas. George

Submitted by ian_macdougall on Tue, 31/01/2017

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Hi George

My U shaped holding tool is made from a 1/4" nail, it will not bend in use. If your mag/dyno body is scrap anyway could you drill another hole in it, or enlarge an existing one, to take the sprag? Bend your nail to suit the spacing.

Ian McD

Submitted by george_phillips on Tue, 31/01/2017

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That's a fair point, Ian (the scrap bit). When you say a 1/4" nail - is it really 1/4" diameter. That's colossal! Mine's made from a longish nail with the head sawn off but I suppose if I can bend it fairly easily to the shape required than it it turn will bend fairly easily when put under stress? Many thanks for your reply. George

Submitted by david_cooper on Tue, 31/01/2017

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You could use a piece of flat steel plate with two snug fitted drilled holes for short lengths of bar - or even bolts. Can be as chunky as you like, and easier than bending a bar...

Just a thought

Submitted by ian_macdougall on Tue, 31/01/2017

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Yes, 1/4" diameter. Your vice needs to be well bolted down! But, as I said, it won't bend in use. David's idea also good. If you think the body might be repairable then maybe you could bolt a piece of angle to the underside of the mag (using the platform bolts) and use that as the anchor for the sprag.

Submitted by george_phillips on Wed, 01/02/2017

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Hi Guys - Success!. I managed to lock the nut with a ring spanner and used a flat punch to tap the inner ring round enough to loosen the nut. Now i've got to rebuild it all in the "new" alloy housing. Thanks for your interest. George

Submitted by george_phillips on Tue, 07/02/2017

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More problems. Magdyno completely dismantled as I need to refit the magneto into a newish body. But inside the body, just behind the larger driving gear there appears to be a bearing race. How on earth does one get it out? It's tucked right up the end of the body and none of it shows through the casing so there's nothing to tap or grip. Any clues would be greatly received. George

Submitted by michael_sullivan on Tue, 07/02/2017

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Most blind mounted bearings are removed by heating the case and smartly dropping it onto a block of wood.

In extreme cases I have seen where two holes 180 degrees apart are drilled in the casing where the outer race sits. Then a small pin punch is used to tap the bearing race out. Then, of course, some method will have to be used to fill the holes.

Mike

Submitted by george_phillips on Tue, 07/02/2017

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Thanks Michael. That's one option I hadn't considered. Plugging the holes will not be a problem. A restful night looms....... George

Submitted by george_phillips on Wed, 08/02/2017

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Well done Mike. Drilled a couple of holes (well 4 actually - 2 missed!) and tapped the race out. The heat/banging treatment didn't work. Now for the reassembly.........George

Submitted by michael_sullivan on Wed, 08/02/2017

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I'm glad it worked for you, George.

I know that i sometimes I engage my mouth without putting my brain in gear.

Stay warm and dry. It has been raining for about a month straight here in San Francisco and I am starting to get cabin fever.

Good luck on your magneto overhaul

Mike

Submitted by paul_wolf on Wed, 08/02/2017

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Previously michael_sullivan wrote:

I'm glad it worked for you, George.

I know that i sometimes I engage my mouth without putting my brain in gear.

Stay warm and dry. It has been raining for about a month straight here in San Francisco and I am starting to get cabin fever.

Good luck on your magneto overhaul

Mike

Submitted by paul_wolf on Wed, 08/02/2017

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Hi George,When you refit the new bearing make sure that you have some support under the front bearing housing because if you start tapping the bearing in you have a very good chance of cracking the bearing housing,i have seen it many times and you must check the magnetisem in the body because if this is weak your spark will be poor.Paul Wolf Magneto Repairs

Submitted by george_phillips on Wed, 08/02/2017

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Thanks Paul. Unfortunately it's all gone pear shaped. The thread socket for the brush holder is smaller than the original so the brush won't go in. The pressure rim appears to cover the holes in the gear ring gear centre so locking the nut is not possible. The armature shaft has play within the bearing at the drive end although the shaft and bearing are original so the new body must be worn. The hole for the HT pick up is on the other side f the body but I guess that's not a problem. All in all I think I've bitten off more than I can chew. George

 


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