I have just had my 1929 flying Squirrel tourer engine rebuilt and, so far, fitting it back in the frame and connecting the chains has gone well. However, when dismantling, the machine, me and two friends did not take enough care with where the cables fit in. Specifically, there are two cables from the magneto which should go to the plugs. Additionally, there is a cable with a loop at one end and a soldered end at the other. I’m assuming this is an earth lead which looks like the loop end should go to the engine casing (secured by one of the screws which secure the painted cover over the chains). The soldered end seems to go to a brass connector with a rubber insulation cap, to what I think is a magneto cut out located under the radiator. This magneto cutout, (if that is what it is), seems to have a series of springs and links which connect it to a brass plate on the exhaust manifold. I have not finished fitting any of the above, as yet, as I’m unsure how to proceed and if my assumptions are correct. Any advice would be most welcome. I hasten to add, this is my first Scott dismantling experience. David Stevenson
It would be easier to help if you could take some detail photographs of magneto, cables and the “magneto cutout” (I doubt that this last item has anything to do with the magneto).
Is it a BT-H magneto on the bike, or a Lucas?.
Normally, three cables are connected to the magneto. The two “thick” cables are the connection between the Magneto pickups and the spark plugs. The third cable is thin, and should be connected to the magneto cut-out – normally a button on the handlebar, which will short-circuit the primary windings in the magneto to “earth”.
Hi, I have previously detailed all this in a Yowl article that is now in “Technicalities”, complete with a drawing of the layout. The thinner lead, from the magneto points cover, goes to the magneto cutout device under the radiator, which is operated by a lever on the left-hand handlebar. The lever also operates the half-compression valves on the engine. When the lever is pulled about half way it operates just the half-compression valves, and when pulled further back it operates the magneto cutout. If you refer to the article in “Technicalities” you will see that setting it up requires a weak tension spring and a stronger tension spring to ensure that the half compression valves operate before the magneto cutout. The spring anchor is NOT on the exhaust flange, but a lot of bikes were thus modified by owners. Look at the front of your crankcase about three inches below the exhaust flange, and below the L/H pipe you should find a 1/8″ diameter hole, angled upwards. This is for the spring anchor to hook into. If your engine now lacks half compression valves there is really no need for the magneto cutout to be under the radiator, and on the last few bikes that I have restored I have substituted it with a 1950s type Lucas stop-lamp switch. This is a lot more water resistant, and it can be hidden away anywhere on the bike, such as under the saddle, or even inside the toolbox, with a short lead to a convenient earthing point. You could also use just a horn push-button on the handlebars as a mag cutout button. Not original, but very few people will spot it !
Thanks Carl And Brian for your very useful replies. It is a BTH magneto. I should be OK now. But, Brian, please can you tell me where to find your article either in which issue of Yowl or in Technicalities. I’ve looked in the latter and couldn’t see anything in the electrics section. It will give me a bit more knowledge on the subject.
It was printed in Vol 16 No 8 in February 1990, a mere twenty four and a half years ago…. Also in Technicalities is a previous similar offering by Jim Best, dated 1967, plus comments printed in subsequent issues, on the same subject.
Thank you again Brian, I found your article in the issue of Yowl and now feel that I can complete the assembly with some confidence. Hopefully, it will start when I’ve finished!