Engine Post-Rebuild Start Up Question

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    After my ’31’s engine rebuild and reassembly, I am nearing the first attempt at starting it. I have sent the instrument panel and all associated instruments to be restored and do not expect them back for quite a while. I have installed temporary instruments: oil pressure and coolant temperature, but I am not sure what to do about the generator. For purposes of just starting the engine, I really do not need the generator, but I don’t want to damage it. What should I do? Leave it disconnected or connect it with an Amp meter and some sort of temporary 6 Volt control device?


    Randy, running with the wire standing in air from the case is no different than the cutout in the off contact position. No harm done. Karl


    I understand; thank you!


    Electrical not my thing, but you might double check. The MoToRs manual states in the general section on generators (not Pierce specific):

    “Open circuit operation: The generator should not be allowed to operate for any length of time with the generator armature terminal disconnected and the field terminal connected. This is open circuit operation which would permit  a high voltage to develop in the generator fields and armature which might damage them severely.”

    The ’31 Pierce wiring guide indicates this is an internally grounded field – so it would be connected – and the armature would be disconnected by the externally mounted relay (cutout) at rest or if the wire was disconnected. The wiring guide indicates that the voltage generated when running should close the relay contact at 7 mph and 7 to 7.3 volts. I think it is not a problem at idle and slow rpm, the relay will leave an open circuit as mentioned, but at high RPM it will generate higher voltages with no load to absorb. There is a thermostatic breaker in the generator field circuit, so maybe that will protect it. I remember on my ’36 Packard when I first started it I left it disconnected and it didn’t damage the generator but blew the fuse in the voltage regulator. On my ’35 Pierce I went ahead and connected the generator wiring to the ammeter and battery to avoid this. Telling you 200% of what I know, so may not be a problem.


    I agree with Jim–do not let the gen run free!



    In the world of generators with the wire hanging free it is running a “wild” voltage ride. This does create heat in time and could unsolder the armature windings. I don’t expect you to drive to Florida like this. Here is a real world scenario of the cutout and output of your generator: When you have a battery tender on your car, the battery voltage is high after an easy start of your 8 cyl. car, with no other lights on the generator is not going to pull the cutout contacts in and “excite” the generator to dispose of its amp load to charge the battery. This is the same as you starting the car with the wire off. If you are in town, at low rpms it can take miles to excite the generator. Your amp guage will show no charge even if it is set for 10 amps or more. Only the 1929 Generator have a voltage cutout in the generator to protect itself from a meltdown. So startup in your garage… real world it’s a test start, If you are still worried, take the cover off and wire back the 3rd brush. No out put.



    I thought about wiring in a temporary generic device in lieu of the normal controls, I just don’t have a good enough knowledge of the way Pierce was controlling things.  Will study and see what I can come up with. My new wiring harness has a lot of disconnected ends so I am basically leaving it disconnected from any power for now. I don’t have the transmission and drive shaft installed so I’m not taking a road trip anyway.

    A lot of first starts I’ve see take place without any coolant in the engine, and I can’t do that; it goes against the way I think, you might say. At least I will have plenty of oil and coolant (plain water with corrosion inhibitor, for now at least).

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