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Re: point gap = ?dwell angle
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Posted by Ken McWilliams on December 01, 2000 at 09:49:48 from (38.232.245.127):
In Reply to: point gap = ?dwell angle posted by Howard on December 01, 2000 at 07:37:17:
Howard, There are several factors to consider including the profile of the lobes that move the points open and closed. On a 4 cylinder 4 cycle engine there are 720 degrees of crankshaft rotation per complete cycles of all 4 cylinders. This gives 720 degrees/2 rotations/4 cylinders = 90 degrees of crank rotation per each cylinder firing. The objective is to achieve enough dwell time to saturate the ignition coil for the next spark and yet have enough gap to break the primary current flow and its associated desire to jump the gap, thus the .020" gap as you called as the specification. These are always compromises to maximize dwell for coil saturation and enough gap to break the circuit while preventing sparking across the gap. The capacitor (condenser)helps in this situation to help break the rush of electrons across the gap,but that's another story. If you will set the gap at .020" and measure the dwell, I would venture to say that the dwell will be around 60 degrees (2/3 of 90 maximum degrees available in a 4 cylinder. Once you've set at .020" and measured the dwell, then record this and use as your basis for setting them in the future. Also, tweak the dwell angle a litte up an down and determine if the tractor runs any better. If happy with one of the "tweaked" dwells, then adjust to that value in the future. Usually, the dwell is adjusted a little to the low side (3-5 degrees or wider gap of .002" - .004") to allow for wear of the rub block which as it wears decreases the gap and increases the dwell. More questions? KRM
Dayton, OH
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