Lucas Mag For Twin: Which Lead is #1, Top Or Bottom

[CarlHungness]

It has been about 15 years since I took off my original mag and replaced it with the B-TH. I may have to re-install it, and don't recall which lead, top or bottom is #1. I think it is the bottom but need to make sure. Since there are new parts on the mag, and some old points in a plastic bag, I think I sent the unit to Doug Wood for rebuild and have not used it since.

 

[Chris Launders]

The body should be stamped 1 and 2, but yes normally number 1 is the bottom one, however I've come across mags where the end housing has been fitted 180 degrees out changing the orientation.
The way to check is when the points are coming into contact with the cam at the end of the longer dip in the cam ring the brass segment in the slip ring should be to the bottom pickup hole.

 

[timetraveller]

You do not have to know, you can check at zero cost. Take off the tappet caps and remove the spark plugs or hold the valve lifter up so that there is no compression. Turn the engine over with the rear wheel and watch the rear inlet valve open and close then, on the compression stroke bring the piston up to just before TDC. The points should just be starting to open on one of the cams. Do the same for the front cylinder and check that the points are just about to open on the other cam. If they are then at least the mag is timed properly and all you then have to do is see which plug lead pick up in in line with the contact on the armateur.