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|Installing Field Coils|
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Finished Block Awaiting Field Coil Installation
At the left is the engine block with the new oversize pistons installed. I attached a bar to the transmission end of the crankshaft to assist pulling it through.
One of the fundamental problems with starting the Model T engine is the field coils. For hand-cranking, the magnets on the flywheel rotate within .025-.040 of the field coils, inducing a low voltage charge that exits the magneto plug on the transmission cover and goes to the coilbox.
In the picture of the two field coils, the old one is oil soaked, insulation is flaking off, and the possibility of shorted coils exist.
Since the engine is apart anyway, investing $140 for a new set ensures you won't have to pull the motor later.
Looking at one of Wally Szumowski's rebuilt field coils you can see new rivets installed.
First, set the field coils on the engine. Tighten up with no shims in to get an idea how far they are off.
Next, somehow get the transmission on the crankshaft end and tighten the four transmission bolts up. Check the gap between the magnet plate and the field coil. Optimum, according to the Service Manual, is .025-.040. Remember the weight of the transmission will always pull downward (as installed) and the gap will narrow on the bottom. I set the bottom to .025 and the top may be slightly larger, perhaps by .005.
If the gap is too large, get a 9/16" wrench and loosen the field coil bolts (yes it can be done with the transmission on) and insert a shim to close the distance between the field coil and magnet plate. Shims are available from vendors in both steel and brass peel-off.
Add shims as required. Wedging a screwdriver between the block and field coil plate will allow a shim to be easily inserted. Unfortunately, after you get the gap adjusted, you have to take the transmission off to tighten and safety wire the field coil bolts.
My son A.J. is safety wiring the field coil bolts after torqueing down and placing cotter pins in the 3rd main cap.
Close-up of the safety wire and cotter pins.
Lift the transmission back on, fit the 4 bolts holding it to the crankshaft, torque down and apply safety wire so the bolts don't unscrew.
Finished product set at .025. Transmission is a product from Russ Potter and has a Turbo-400 clutch in it. After 3 years of use it has a positive neutral and still shifts great!