I’ll assume that if you have a 60+ year old tractor that you have a test meter.
I have discovered that 75% of “no spark” problems on frontmounts are as a result of poorly aligned parts or wires & not parts failures. Remember, you are dealing w/ parts made over 60 years ago that have seen a lot of wear & tear. They just don’t fit together like they used to.
First, turn the key on & crank the engine while you look at the ammeter. What is it doing? If it fluctuates, that means your points are opening & closing. If it shows a constant discharge, or doesn’t move at all, that means you need to do some more checking.
Next, check for voltage at the top of the coil. Battery voltage w/ the points open & about half of that when they are closed. If you do not have voltage to the coil, then move upstream to the resistor then to the ignition switch. As you check each component, wiggle it & the wires attached to it & watch you meter. Resistors break or get shorted & wires corrode.
If the voltage never drops when the engine is cranking, that means the points are not closing or you have lost contact between the pigtail & the brass screw or the tab & the cap.
Next, check for continuity inside the distributor w/ a meter. It is very easy to ground the tip of the condenser wire to the body of the distributor when you replaced the points. Also, make sure the condenser wire does not go through the same opening in the distributor that the coil pig tail does. The condenser wire goes the opening on the top right. Look at the points; are they burned, pitted or mis-aligned? Check the point gap, .015 on all four lobes. Make sure you are using quality parts; the points should have a phenolic rubbing block & not the cheap white plastic crap. Make sure you have the star washers under the screws on the points.
Next, with the distributor still off the tractor, install the coil. Look at the pigtail on the coil; is it touching the brass screw w/ the concave head inside of the distributor? Don’t trust your eyes; test for continuity from the top of the coil to the points. If you do not have continuity, stretch the pigtail a bit until you do. (some people would rather put a small washer under the brass screw) Make sure that the pigtail is not grounded to the clip that holds the distributor plate in place; sometimes you can move the plate while setting the timing & actually ground the pigtail. Your meter should tell you this even if your eyes don’t! Also, look at the little tab opposite of the pigtail; bend it a bit also to insure that it will contact the distributor cap. Another common failure point is the insulator in the tab on the distributor plate where the brass screw w/ the concave head goes; it holds the copper strip from the points. Again, your meter will usually tell you if you have a problem, but you might have to wiggle the copper strip a bit. Once you are sure that you have good continuity inside the distributor, you should be good to go.
At this point, I just put the distributor, coil & cap all back on the tractor as a unit (it helps to do this from the left side). The reason I do this is because it is real easy to get the cap or coil mis-aligned trying to put it back together one piece at a time & the result is something gets broken or you get a ‘no spark’ problem.
As to the resistor, p/n 12250 or 12250B (the resistor on the terminal block) it should read .3 ohms cold & 1.7 ohms hot.
Post back w/ results & any other questions.
50 Tips
