Author Topic: magneto  (Read 1086 times)

Offline RDfella

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Re: magneto
« Reply #30 on: 24.05. 2019 18:35 »
Chaterlea John was correct as usual.
A couple of weeks ago I got around to turning up a mandrel to locate the mag end cap on its cam ring bore. I kept it a thou or so oversize and warmed the casing so it’d grip the mandrel. Also cut a slot for the camring locating screw, to act as drive peg should the cap try to slip whilst being machined. The idea was to rebore the armature bearing so the camring would be concentric with the armature. I was amazed how much out of true it all was. The bearing bore clocked .005” (.0025” off centre) but the real culprit was lack of squareness. I had to take .020” off the flange that locates on the mag casing just to get it to clean up. I also deepened the bearing bore a similar amount, as I didn’t fancy making any more of those outer shims.
Today I re-assembled the mag and remounted it on the engine. Success, the points gaps are now equal and the timing between cylinders spot on (instead of 20* difference). What amazed me was the amount everything was out of kilter. This was not wear or abuse, but sheer bad machining from new. Casting the cap would be dead easy and machining it should only require two or three jigs, so why Lucas made such a pig’s ear defies understanding. Maybe there was crud in the jig that didn’t allow the casting to sit properly when the ‘technician’ did his particular part of the manufacture. Wonder how many came out like that before quality control or the shop’s fitter spotted the problem
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Online Triton Thrasher

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Re: magneto
« Reply #31 on: 24.05. 2019 19:17 »
Can you engineer something better than the paper daisies, to insulate the bearings?

Offline RDfella

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Re: magneto
« Reply #32 on: 24.05. 2019 20:12 »
Agree, those bearing insulators are a real pain. As expected, first fit of the bearing wrecked the gasket so had to get another (should have some somewhere but can't find them). Always had hassle with those gaskets / insulators - the trouble is that despite bending the tails around the bearing first, the gasket still tends to slip sideways so that one side is still halfway out. I believe ceramic insulated bearings are available, but they wouldn't be our type and the mag would need modification to fit them.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Online groily

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Re: magneto
« Reply #33 on: 25.05. 2019 07:09 »
They are a pain RD - but they do come in 2 thicknesses, and usually with a warmed housing and the nearer fit of the 2 they'll slip in OK, especially the ones with a shiny outside surface.  A non-ferrous mandrel on the end of a non-ferrous bar (with a nose to retain the oil seal over the race and insulator for drive ends) will ensure centralisation.
One of the commonest reasons for problems at the cb end is the skewed fitting of bearing insulators, messing up the concentricity of the outer race viz à viz the housing.
Bill

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Re: magneto
« Reply #34 on: 25.05. 2019 09:22 »

 
Quote
......This was not wear or abuse, but sheer bad machining from new. ...........

 That machinist deserves a DCM...... *eek*
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Online Greybeard

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Re: magneto
« Reply #35 on: 25.05. 2019 18:26 »
That machinist deserves a DCM...... *eek*
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Re: magneto
« Reply #36 on: 25.05. 2019 19:11 »
Don't Come Monday in other words sacked, fired.
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