AJS & Matchless Owners Club

Hi all,

Whilst embarking on my 2 engine rebuilds, I'm contemplating a Mag change on my '55 G80CS. It has the racing Lucas on it, however, I've been reading and found that the BTH's of yesteryear, apparently performed better at low revs particularly, and, were as strong higher up the rev range. I like the idea of that on my '55.

My short stroke has a freshly rebuilt Racing Lucas, and it seemed strong for the 5 mins I rode it before the primary chain broke, and oil line blew off the top of the motor! ahahaha.

In any case, what is the consensus regarding BTH's Vs Lucas? And, which model would I need in BTH to replace my pad mount Lucas?

Cheers.
Marty

Wouldn't change it for no good reason Marty. Nothing wrong with either type. people liked BTHs for various reasons (closer tolerances in the manufacture, continued use of mica condensers after Lucas had gone to rolled paper) etc etc but the performance differences are absolutely minimal. If we're comparing an NR1 to say a BTH KD1 or similar, I can't see any reason at all to swap. The Lucas will produce excellent sparks from just over 100rpm of the mag, or should, and the BTH will do the same. They'll both rev happily away to the 3000-3500 mag rpm (and beyond) which equals 6-6.5K engine revs. And with the rotating contact breaker & ringcam on the R series and C series Lucas N mag, there is no obvious benefit in installing a similar size, similar design, rotating cb BTH.
My tuppenceworth.

I thought you were going to discuss the "new" BTH electronic mag for a moment. This is a beautiful and super accurate piece of equipment which looks sort of similar to an NR1 but can be timed very precisely since the spark is so well defined , and is a single discharge, not a whole shower.

It also has its own internal advance retard which is in the software I think, so very convenient.

Thery are making a look-alike K2F now which is working great on my M31, and looks nice too. First kick starting.

Disadvantage is that they aren't cheap, but the effect is transformative.

Steve

I agree with the last comment...The new BTH mags are brilliant.....Have them fitted on both of my Matchless scramblers for over ten years ....Now no problem starting and the mag regulates the ignition by itself ....Before I had two original Lucas Competition mags....the spark was good enough to weld with, but the bikes had problems starting...also the New BTH mags are great coming out of corners.....so smooth instead of having the ignition on advance all the time...You cant play with an advance and retard lever while racing.....So my advice....mortgage the house , put the wife out to work and get one