US Motors Army Signal Corp

[Jerry Park]

I have a WW2 Signal Corp generator. The data plate says 12.5 kw PE78 G. I hope to get it going again but it looks like a big project . The engine is stuck and three spark plugs are rusted in place.Has anyone had any experience with this gen set or have information pertaining to same.Its plenty heavy.
Jerry park

[Doogdoog]

Aloha,
First you have to determine if the gen is stuck or the engine, I would separate them to find out. Most likely it is the engine but who knows? Ok, I would put some auto trans fluid in the 3 cylinders by removing the sparkplugs and soak the other 3 sparkplugs with penetrating oil for about a week. It's best not to be too aggressive (don't want to break anything) so take your time and let it soak.

Mahalo,
doogdoog

[Jerry Park]

Thanks for the reply.I haven't done much with it since last summer . I have been soaking the cylinders with an oil and diesel-gasoline mixture.Three of the spark plugs are just nubs from rusting away.I think I will have to pull the head to take care of that problem. Uncoupling the generator is a good idea.I hadn't thought about it being stuck but rodents may have lodged stuff around the stator as well.I thought I would first try to get the engine issue resolved and then look into the generator.It had been used by a construction company and was working when it was set aside for 30+ years. It was partly covered except where the exhaust stack went out and thats where water came in and rusted the three plugs.Some rain proably went into the cylinders as well through the exhuast.I dont know if the generator windings will still be well insulated enough being over 60 years old and through many generations of rats.The engine must be a JXB as that is cast on the base.And I think the rpm's is 1200 so it should just cackle along puting out its rated power.

Jerry

[Jerry Park]

Went ahead and pulled the head today.The cylinder that had an open exhaust valve is rusted worse. It may require a rebore and oversize piston or a resleeve.The question is are parts available and is it worth the cost.When you start puting money into it then to do it right a total rebuild may be needed.I haven't looked at the bottom end yet.I guess its up to the indivual as to how much its worth to restore something.Once you start theres no looking back but its all for the fun of it anyway.
The data plate on the exciter is a different company than U.S. Motors but the same specs. Any info on this?
Jerry

[Rich Mc]

Your stated engine and generator are the correct types for a PE-78-G. The Signal Corp Technical Manual is TM-911
The generator is 3 wire revolving field using 2.65 gallons/gasoline hr @ rated load. Weight is spec'd @ 2050 lbs and was used at fixed installations for communications equipment.

[jdunmyer]

Jerry,
I couldn't tell from the pic just how bad that bore is, but if it isn't pitted too badly, I'd hone it, install new rings on the piston, and hope for the best. You might be surprised at how good it works, especially beings it runs at only 1200 Rpm.

This is assuming that you're going to use it for standby operation, just a few hours/year. If you're planning on running it 24/7 for long periods, you'll probably want to have a shop bore and sleeve that hole.

<<Jim>>

[Jerry Park]

I am going to pull the pan and valve covers and see what that part of the engine looks like.Like you say if I do run it it will mostly be for hobby intrest any way. I think I am getting more interested as I get deeper into it.I can visualize what it would look like painted up nice and what it would sound like humming along at 1200rpm.I don't believe the engine has a lot of hours on it.I separated the generator head from the engine and it turns free and the bearing seem good.The brushes and slip rings need to be cleaned up.The windings look OK but the varnish is old on the windings.Is there some kind of special red insulating spray paint for coils ?
Jerry

[jdunmyer]

I've often dried out motors with a battery charger, just connect and set it at a few amps and let things cook a while, at least overnight. I'm unsure of where and how I'd connect the charger to a generator, but the principle is the same.

An alternative would be to warm it in some other way to drive the moisture out. Heat lamp(s), electric heater blowing on it, or...??

[Jim Rankin]

http://www.eng-tips.com/viewthread.c...=173511&page=2

link to a discussion of drying techniques for generators.

There is aerosol spray red insulating enamel. Try your motor shop or electrical supply. I would megger and clean, and then dry and megger again before the spray.

[Elden DuRand]

Originally Posted by Jerry Park

I am going to pull the pan and valve covers and see what that part of the engine looks like.Like you say if I do run it it will mostly be for hobby intrest any way. I think I am getting more interested as I get deeper into it.I can visualize what it would look like painted up nice and what it would sound like humming along at 1200rpm.I don't believe the engine has a lot of hours on it.I separated the generator head from the engine and it turns free and the bearing seem good.The brushes and slip rings need to be cleaned up.The windings look OK but the varnish is old on the windings.Is there some kind of special red insulating spray paint for coils ?
Jerry

Jerry:

If the bore isn't pitted too badly, I'd go along with the idea of freeing the piston, cleaning up the bore and replacing all the rings.

After you get the bottom end cleared, be careful trying to crank it if it seems to still be stuck or has a tight spot. Could be a stuck valve!

Products like "Sprayon" number S00600 Clear Insulating Varnish or Krylon clear acrylic spray will seal the windings but you might be better off if there's a motor rewinding shop close that can check, dry and vacuum impregnate the windings.

In any case, have fun!

Take care - Elden
http://www.oldengine.org/members/durand