Forum

[simon]

They are the ultimate magneto design fixed coil, moving magnet, ordinary set of points. Mine hasn't missed a beat. Prepare though to clench when you buy the auto advance unit as it won't be cheap and is vital. The oil leak on the aluminium machine turned out to be the oil feed to the exhaust rocker. I must have damaged the sealing washer. So all good there. S:)

[Alan R]

Hello SIMON---- I've not actually seen an SR1 "up close and personal" so to speak but would it be possible to fit a manual control cable for the advance/retard maybe ???

[simon]

I don't see how Alan, although if you could modify the points mounting so that it could be cable controlled? It's obviously not as good as moving at the drive side because with the auto advance unit the mag is always kept in its optimum output sweet spot. They were used on all sorts of agricultural machinery so maybe there are some manual advance ones. I have to say that the auto advance is a nice unit and its nice to know that the bulge in the timing case is actually housing something it was designed for.

[Chris Tindal]

Simon, enlighten us. I have noticed that the very first 1948 prototype bullet had the bulge, then it was dropped until 1956. What's the difference between a mag dynamo and an SR1? Why didn't the 49 to 55 bullet have it?

[simon]

The Mag/Dyno is an earlier beast than the SR1 which was I believe the last Lucas mag produced. The Mag/Dyno (which incorporates both the magneto and the generator in a single unit) in my experience has used an N1 magneto that has a cam ring that opens the points that are attached to the end of the armature. The magnets (Aluminium/nickel hence the N name) were contained in the body of the magneto. This means that you can easily advance and retard the mag by moving the cam ring back and forth. This didn't prevent the installation of an auto advance unit which is a bob weight controlled device that works on the drive sprocket (better for spark continuity) so I imagine that's what the early bulges were for. I had both a manual and an auto advance on an M16S I owned years ago and it was rather a good combination as you could retard the ignition a bit for a long hard pull up a steep hill. It sort of compensated for the lack of a vacuum advance mechanism. The SR1 as I mentioned was the last of the mags and it had a couple of major advantages. For a start rather than having the windings all spinning at high rpm and the condenser hidden in the middle the magnets spin and the coil is a nice simple stationary unit. The points and condenser are standard distributor types and the whole unit was easily reversible by simply moving the points cam. They fitted these to the Bullets for just two years 1956 and 1957 when they made the improvements to the older style motor. I imagine the cost was too great and hence the battery and coil mod and the redesign of the timing cover was also considered too expensive so hence the many years of the unnecessary bulge.

[Chris Tindal]

Thanks Simon, electrics aren't my strongpoint so its interesting to get an insight.

[Mark M]

Simon has covered it pretty well but although the SR series of mags (there was also a twin and a four, and maybe more?) may have been Lucas' last new design it wasn't their last magneto produced, my 1966 Mk1 Interceptor has a K2F magneto with auto advance (a much earlier design,) with a date stamp of October 1965. I think the SR was expensive to make (as were all mags compared to points and coil,) and certainly because of other considerations (low kickstart speeds not providing a big enough spark,) weren't a big success on the Twins. Interesting though! REgards, Mark

[simon]

Yes true, I should have said the last designed rather than produced. And I've seen SR2's and SR4's on tractors. There is a firm that make a copy new under the BTH name (how the men at British Thomson-Houston would turn in their graves to be manufacturing a Lucas copy) with rare earth magnets and an electronic advance which would be a splendid devise and would throw an enormous spark. Rather pricey though I believe.

[Mark M]

Simon,I have to say the K2F on my Mk1 (rebuilt though!) throws a corking spark especially through Iridium plugs. These were NDs by the way, built for non coil applications. Incidentally, the guys at the Spark Plug Company said that Iridiums will still give a better spark even if designed to run on a coil system. Using them my bike is an easy starter so I will use them on some of my others too! REgards, Mark

[Chris Tindal]

Mark should my 58 500 engine have an SR1?