Lucas Mag' Earth Brush Holder Thread
- Thread starter cinquecento
- Start date
A little difficult with an ordinary mag (points) as a variation in points gap alters the timing, you would have to ensure they were exactly the same every time.aqqqqqqqqqqqqqqqqqqqqqqqqqqqq
Sorry about that the kitten decided to walk across the keyboard just as i pressed post.
Some years ago our much-missed previous dog shoved her way past my chair to a spot at my feet under my desk just as I was about to hit 'send' on a long email I had carefully composed. As she plopped down the screen went black and the computer powered down as she pulled the power cord from the wall. I repositioned the power cord after that incident.
But back to the, ahem, point. The slope on a Lucas magneto's cam near the point... I mean, location where the points open is 0.0017 inches/degree. If you have your gap set, say, 0.0034" too large, they will open 2 degrees magneto -- 1 degree engine -- later than you intended.
Cam rings never wear the same , the grinding of the cam is very hard to hold EXACT measurements. the center of the armature would have to be EXACT which they never are, that is because the armature is supported by bearings where the outer races are supported by insulation paper , it is hard enough to support the outer race in a metallic bore , lit alone a paper one. For the armature bearings to hold a true and EXACT center of the armature in its housing you would to shim them to a zero clearance, which would cause instant failure. The needed clearance to prevent this causes the armature to SAG moving it off center to the outer race bores of the housing. In my experience over 50 years I have never found or been able to build a Vincent mag too Exact 50 degree apart openings of the points.
Sadly, neither.
Lucas specified zero clearance as ideal, with 0.005" max. for a magneto with a ring cam. This is consistent with the materials used in the construction as well as my measurements of the differential thermal expansion of the armature and housing. The armature is essentially steel which expands less than the housing which is essentially Al. Because of this zero clearance when it is assembled, which does not cause instant failure, increases to a positive end float as the magneto gets warm.
As for not being able to get the openings to be exactly 50-deg. apart, doing so requires specialized instrumentation that most people are not likely to have. With such instrumentation it isn't particularly difficult.
My shop is pretty complete,what instruments may they be? How can a instrument correct a mechanical impossibly?
As an example of something I use for this that is unlikely to be in your shop, take a look at:
http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=459849#Post459849
It's interesting that an instrument like a Talyrond is so readily available since most places that own one wouldn't let anyone but a trained operator near theirs. But, if all those instruments are available to you then you should be able to get the points to open 50-deg. apart. As for a "dust up," the other guy sells a replacement condenser that I don't recommend for technical reasons I went into in some detail and he doesn't like the fact I don't recommend it.