I delayed the starter wiring as long as I could in order to avoid accumulating a lot of unnecessary play time on what might be a limited life starter. However, there's something really neat about an electric starter on a model engine, and I ended up running down two 12 Amp-Hr batteries while 'testing' it. I could be using a battery with more appropriate capacity (and terminals), but the ones I have might be a little less stressful on the engine's starting system.
Afterwards, I removed the manual starter shaft and bearing housing so I could inspect the starter bevel gears which are all visible from behind the cover. I didn't yet see anything suspicious about the teeth - just the expected wear patterns on their phosphate coating. The patterns looked normal, and so I just re-coated the gears with gray moly grease and replaced the cover. I also filled the oil tank so any further cranking could begin pumping oil throughout the engine. I allowed the engine to sit for several hours with the oil tank's ball valve open so gravity could help prime the pressure pump. The copper oil distribution lines were previously filled with oil when they were installed, and so all that was left to do was to pre-fill the oil filter.
The good news was that the high pressure oil gage was now registering a couple psi while cranking the starter. The bad news was that I had a pretty significant oil leak on the underside of the engine. Even though it's been in plain sight ever since the lower crankcase was assembled, this leak has been difficult to pinpoint because of its totally unexpected location. Oil has been leaking from the bottom machined surface of the scavenger pump because of an imperfect fit of one of the bronze bearings pressed into the aluminum pump housing. The bearings for the pump shafts were pressed into the housing's workpiece before any machining was done. The floor of the housing ended up rather thin after machining, and this evidently uncovered latent damage created by a poor pressing operation. I had been assuming all along that the oil on the underside of the pump had been coming from far more likely places above it.
My fix was to JB Weld an aluminum plate to the machined bottom surface of the pump housing. The outer contour of the plate was machined to match the pump housing so it would completely cover the bottom surface of the pump and look as though it belonged there. After installing the plate, the engine's underside finally remained dry.
I then completed the machining of the rear and front plates that make up the electrical panel. Cutouts for a panel voltmeter and four toggle switches were machined into the rear plate. The voltmeter monitors the battery voltage; and, in addition to a main power cutoff, the switches apply power to the magnetos, fuel pump, and radiator fans. The outputs of the switches on the rear plate connect to their loads through blade terminals on the front plate. A pair of connectorized cables between the front and rear plates compete the circuits between the two while allowing the panels to be easily separated for maintenance.
The fuel pump was mounted to the front side of the front panel. A buck converter located on the inside of the rear panel supplies voltage to the pump motor so the fuel flow can be regulated. A screwdriver adjustment, accessible on the rear panel, controls this voltage and the fuel flow.
Including the tach, two CDI's, and three buck converters, there's a lot of electronics associated with the electrical panel that could be damaged by an inadvertently reverse-connected high capacity battery. Therefore, I added a protective diode in series with the main power switch. I was able to come up with a Schottky power diode that had only a .3V forward drop at 3 amps of current.
During testing, I ran into a problem with the starter wiring. When I wired in the starter relay I had forgotten that one side of the motor's brushes was grounded to the motor housing. I managed to wire the relay into the wrong side of the motor, and all was well until the negative side of the battery's accessory loads were connected to the chassis. This inadvertently bypassed the starter relay and caused the starter to be energized as soon as the battery was connected to the terminal block. Pretty much all the starter wiring had to be re-done to correct the problem.
The build's final steps are soon coming up and will include the fuel tank and a system to fill and drain it. -Terry
