Low-Tension Mag Starting

| July/August 2003

  • SmokStak

  • Magneto/battery hookup
    Schematic for magneto/battery hookup as shown in an old United manual.
  • Magneto hookup
    Schematic for magneto hookup only.

  • SmokStak
  • Magneto/battery hookup
  • Magneto hookup

The following comes from a recent topic on SmokStak, an Internet engine bulletin board (go to http/ smokstak.cgi). As ever, various individuals started, commented on and concluded the following bulletin board thread.

I have a really nice, barn-fresh Associated with loads of character gained through the years. It runs great, but it's a real bear to start. I would like to start it with a battery and coil and then switch it over to the mag. My question is, should I install a two-way switch to switch between the mag and ignitor or should I install a two-pole, two-way switch so I can ground the magneto when the battery is in use? Will I need a resistor in the grounding circuit so the mag is not shorted directly to ground, and what size and value of resistor might I need? -Al

A single-pole, double-throw switch will be just fine. There is no need to ground a low-tension mag while the engine is running. The AC voltage generated by the mag when not loaded will be quite low compared to the spike created when the igniter trips. Bearing condition is critical in low-tension mags, as is strength of the magnets, and it must be correctly timed to the engine. I would guess you have a problem in one of these areas. - Ken

Thanks Ken. This engine is in 'as found' condition and I have done nothing to it. The mag timing is good, but the magnet could be weak. The armature bushings are a bit worn, but not so much as to allow dragging on the fields. This thing is completely original and I want to leave it for the next generation to restore. I am not even going to clean it. I had it mostly apart and repaired the rod bearing and the wrist pin. It is a lot of fun to run and people point and laugh at it. I just love it. - Al

Yes, some of the nicest running engines I have seen were in 'as found' condition. Nothing wrong with that, it shows how these old engines spent most of their working life. It's getting hard to find engines and the old, larger tractors in that condition. -Ken

I just installed a rebuilt gear-driven mag on my small Associated. I measured the voltage from it while the engine was running off the battery and coil and got about 5 volts. This sounded low. The engine will run off the mag if the rpms are kept up and will start a crank if you turn it fast. Does this sound normal? - Mike


Gas Engine Magazine A_M 16Gas Engine Magazine is your best source for tractor and stationary gas engine information.  Subscribe and connect with more than 23,000 other gas engine collectors and build your knowledge, share your passion and search for parts, in the publication written by and for gas engine enthusiasts! Gas Engine Magazine brings you: restoration stories, company histories, and technical advice. Plus our Flywheel Forum column helps answer your engine inquiries!

Be sure to take advantage of the Square Deal Subscription Program.

  • No Missed Issues.

  • No Renewal Notices.

  • No Additional Cost.

The Square Deal Subscription Program is designed as a paperless transaction with automatic renewals at a preferred low rate.   With advanced electronic notification, a 100% satisfaction guarantee and an easy opt-out plan, the Square Deal Subscription Program is the best value, risk free, eco-friendliest way to subscribe.

Facebook YouTube