Jake, Thanks for posting this. I will try to find and post the great dynamic video which is available showing how the fly/coil works. This article should clarify how a DVM is set up to test. Impedance cannot be measured directly if I remember theory correctly. And Briggs does not discuss the enemy , "heat, " the big killer.
Jake, Well, interesting what Briggs says about heat. Their heat is runaway current beyond what the little transistors can stand. The heat I always mention is just engine generated, but have never tried to measure the heat at the coil after a hot summer day mowing. The placement of the coil is certainly away from the exhaust and is fanned. I think I read a good transistor junction can only stand around 250F. An engine plugged with weeds and low on oil can get hot. I have measured 310F at the spark plug hole with good fan and oil level. Can high "heat soak" reach the coils? A good question.
Correct again, but there is two kinds of heat that damage sensitive parts. Engine heat and electrical short circuits. I have seen a damaged high tension lead from the coil to spark plug fry a coil if the lead is shorting to the engine block. My original post shows an impedance test for the coil and mentions that it should be done at room temperature, and the preceding paragraph states: As coil temperature can aggravate minor coil imperfections that normally wouldn't be a factor. Heat is our enemy! My 8hp briggs I/C has a deflector attached by one of the coil mounting bolts, I wonder if that is suppose to cool the coil?
Jake, Gross lack of experience with various mowers here, but I would guess the more compact the engine the closer the coil (s) to heat. In my Intek
V there is lots of space and heavily heat sunk iron parts where the coils are, so perhaps less a problelm.
