Debating the purpose of a magneto impulse.
In the June 2008 issue of Farm Collector, an Iowa reader inquired regarding a kicking problem associated with cranking an old Regular Farmall tractor. In the August issue, Oren Glatt, Abilene, Kan., provided his answer based on years of service experience on WICO and Fairbanks magnetos, both of which were never original equipment on IHC tractors but could be added as aftermarket.
With respect to Mr. Glatt's years of experience, I totally disagree with his response. I quote from his letter, "The impulse on magnetos was designed to give an extra 'kick' or intense spark in order to get the engine started." This was not the original purpose. The intensity of any mag is based on the quality of the coil, quality of the condenser and the finite adjustment of the points. I can neither prove nor disprove an increase in intensity as the result of an impulse nor can I prove or disprove his magnetic theory regarding an improperly working magneto impulse.
An IHC E4A magneto as original equipment on the regular Farmall had no condenser but had an impulse manually engaged by the one doing the cranking. The later F-20 Farmall using an IHC F-4 mag had a condenser and automatic impulse that worked most of the time. When it failed to engage properly, a slight tap on the case next to the impulse usually provided a remedy.
The 4-cycle, 4-cylinder engine of early Farmalls was set at the factory to provide current to the spark plug from 8 to 4 degrees before top dead center. A running engine rotates partially from kinetic energy derived from a revolving flywheel. Therefore, pre-imposed pre-ignition presented no problem. Advance the timing and a ping or knock may ensue. Retard the timing significantly and while idling, the engine will reach a boiling point. Timing is of the utmost importance.
The sole purpose of the impulse, when properly engaged, is to keep the mag momentarily from rotating and firing the spark plug until the piston is a few degrees past dead center. In this position, the piston is beginning to move downward on the power stroke. Therefore no pre-ignition will take place and there will be no kicking.