The Delco Model-750, 32-Volt Power Plant


Delco expert Don Wiley identifies it as a Model-750.  He says they vibrate something fierce when running and that's why the relay panel bracket is broken on this one.

This model Delco generator never had a 32 volt battery attached to it.  They used only one 6 volt battery to run the small starter that is hinged to "flip" into the groove in the flywheel when the system calls for "start". 

When the engine started and got the voltage up to 29 volts the starter relay dropped out and the starter would fall away from the flywheel.  When the load was turned off, the ignition was disconnected from the coil through a relay and the unit would "reset" waiting for the next light or load to be applied.

Don says that they must run around 1300 rpm to generate the needed 32 volts.  The book says 1250 to 1400 rpm.   Don adds that he used a car wheel spin balancer and added lead weights to the flywheel but his Model-750 still vibrated like crazy. 

October 2004:

This one needs a little work!  We tore it down in August 2004 and know that it has very few hours on it.  Low hours doesn't mean that it is in good shape.  The piston was stuck (water was standing in the cylinder), the exhaust rocker is broken because someone tried to crank it with a stuck valve and a piece of the exhaust valve guide broke off sometime in the past and was still rusted to the valve stem.

Before Frank got it, it sat outside for quite a while.  At first, I didn't think it was worth the trouble but, after looking at it, I think it can be restored.  The big asbestos core ballast resistor is broken and the control relays are dirty but they look to be intact.  All the wiring needs to be replaced.

The commutator has no wear on it and the bearings look good even though the crankcase was full of water and sludge.  There are some rust issues with the cam and tappets but these are fixable.  The governor is a rusted-up glob so, before looking for another, we're going to try electrolysis on it.

Here are the data plates we could find.  The number on this plate is 337 19336.  Is this the model number?

Here's the serial number plate.  The number is 278587.  I suppose it can be dated from this.

Looking at photos of other Delcos, I think this one is unusual in that the control panel is not mounted on the generator frame but is mounted on the base board with angle iron brackets.

During September and October, we tore it down.  I finally got the piston unstuck.  

2 July 2005:

Well, yesterday, I finally got started on the cleanin' and fixin'.  

The cylinder had a badly pitted area just where the top of the piston was.  Also, the intake valve was almost rusted away.  After doing the electrolysys thing on the cylinder and giving it a good honing back last October, there was still a pitted area but we decided to let it go rather than bore and sleeve it.  We'll see once I get it running, if that was a good decision.

Here's the cylinder after I reground the seats, and put in the new valves.  Note the pitted area toward the top of the cylinder.

Note the top of the piston where the water stood for a while.  Kinda corroded!

The Delco has a float-type oil level gauge.  There was just a fragment of the original cork float remaining so I'm doing an experiment.  I've made a new float out of a couple of stoppers from cheap wine bottles (after making medicinal use of the contents!).  These stoppers are made out of a soft but dense closed-cell foam.  I tested them by soaking them in mineral spirits overnight.  They survived fine so in they go.

The oil level assembly has to be installed before the crankshaft because there's not a lot of room to hook the float(s) to the arm of the gauge.  The floats have to be put on the arm after the arm and indicator is in place.

In spite of all the water inside the engine, the crankshaft, camshaft and other parts were hardly rusted.  The flywheel end main bearing (a big double row ball bearing) had rusted, though and was very rough.  This bearing has a standard inside diameter but the outside diameter is oddball, apparently so folks would have to go to Delco to get them.  Luckily, we found a new bearing.

I went over the crankpin with a strip of worn-out 400 emery paper to get the little spots of rust off.  There was virtually no wear on either the crankpin or the generator end main bearing (a babbit sleeve).

The block is cleaned-up and painted and I've got the crankshaft and cam in place.

Next, I'll bolt on the flywheel.  I have to do that before I can put in the rod and piston and bolt on the jug, because the lengthwise position of the crankshaft is determined by the ball bearing inner race being clamped between the crankshaft cheek on the inside and the flywheel flange on the outside.

3 July 2005:

I made some more progress today.  


The camshaft is held in place by the governor housing.  End play in the camshaft is set by adjusting the thickness of the gasket that goes between the governor housing and the cylinder block.  After cleaning up the mating surfaces, I laid the parts together and used the feeler gauges to determine how thick the gasket has to be to get zero clearance.  The 0.016" feeler just slipped in there.  

Tapping out the gasket using a small hammer.

Figuring it would be nice to have 0.010" or so of end clearance, I made a scientific decision and went to the gasket material shelf.  The closest I had was 0.031" thick so, I now have about 0.015" clearance (minus gasket squash).  Perfect!

The governor assembly screws into the end of the camshaft with a right-hand thread.  It doesn't need to be super tight.


Before hooking up the connecting rod and assembling the jug, I took a look at the tappets.  As you can see above, they had some rust pitting on the surfaces that contact the cam lobes.  I hadn't noticed this when I disassembled the engine.  The rest of the surfaces of the tappets were good and, not wanting to wait for new (good used) parts, I decided to use an old method to refurbish them.

First, I removed  most of the pits by carefuly grinding them on the side of the fine wheel of my grinder.  The secret here is to take off a little at a time, turning the tappet all the time.  I used a machinists square as I ground them to make sure the rubbing surface was perpendicular to the tappet body.  It's hard to get them perfectly perpendicular but you can get close enough for a Delco.


Then, as shown in the photo above left, I used 220 grit carborundum paper to polish out the bigger scratches from the grinding wheel then went to some worn out 400 grit paper for the final finish.  You don't need to remove every last rust pit or get a mirror finish.

Make sure to use a random circular motion as you polish so as to keep from tilting the surface.  I think that doing it this way also gives the end of the tappet a slightly convex surface which should help to make them rotate.  The above right picture shows the tappets ready to install.

I learned something about Delcos today.  It's a real chore to hook-up the rod.  There's very little room to put your hands.  I ended up holding the rod cap (minus the shim packs) to the crankshaft by using a stiff piece of wire bent so it was a friction fit in one of the bolt holes.  Then, I laid the rod to the crankshaft and, with difficulty, got one of the bolts started.  Then I slipped the wire out of the hole in the cap, set the shim pack for that side in place and started that bolt.  I took out the first bolt and put that shim pack into place (after dropping it into the crankcase once!!!!!).  I started that bolt and drew them both down evenly.  Needless to say, there was some rather uncouth language used during this process.

And here it is.  Breather, rocker box and exhaust are in place.  I'll have to take the exhaust back off when I put the cooling chimney on.

Next time, I hope to finish painting the chimney and cap and get them on.  The carburetor needs to be completely gone through and the points need to be set before it's ready for a test run.  I'm going to use one of my Solid-State ignition modules with the Delco points to fire the original Delco coil so I don't have to go out and buy a 6-Volt battery.  

I'm hoping I can start it by simply pulling the flywheel over.  We'll see.

5 July 2005:

Today, I got the engine mostly put back together.  I took the carb apart and cleaned out all the rust, mud dauber mud and goobers then put it back together again.  When I went to hook up the governor linkage, I found that there's a spring missing from the throttle shaft and I suppose I'm gonna have to do some shadetree engineering.


What I need to do now is reassemble the generator fields and armature.  Since the control panel is in really bad shape and I'll have to totally go through the relays and wiring, I'm not going to put the brushes back in the generator so I can run it without those little items.  Then I can  mount the coil and go through the usual gasoline leaks, oil leaks and last minute goof-ups that go with getting it running.  

6 July 2005:

Today, I made the revoltin' discovery that the idle adjustment air valve is broken off.  I found this out when I was reading the operating instructions!

I used an easy-out to remove the remains of the needle and, since it looks like the body of the valve is buggered-up, I re-tapped it to 10-32 and made a new needle.


The picture above left shows the new needle and spring.  The piece of the old needle is also shown.  It should work okay, although I'm looking for an original one.

30 July 2005:

Well, after taking a close look at the field coil wires, I decided to put-off reinstalling them until I have some original looking wire.  In the meantime, I bolted-up one of the field coil pole pieces so I could mount the ignition coil.  

Today, it ran for the first time in a LOOOooooooong time!


Since we haven't decided how to manage a gas tank, I'm using one of my "temporary specials", made of a mineral spirits can with a piece of copper tubing soldered into the bottom.  High Tech!

It was a little hard to get started the first time by pulling over the flywheel.  This was because of low compression and, when the timing is set to the factory mark, it is a bit fast and wants to kick back.  I retarded the timing as far as I could (this is done by adjusting the point gap), to just a little before TDC and after getting some pops, snorts, other rude noises and working up a sweat, it decided to run.  It ran real weak 'til it got to somewhere around 300-400 RPM but above that, it seems to want to run.  That's probably a result of valve timing, etc.  With the electric starter, it should crank fast enough to start readily.

I've been told that these Delcos are real shakers and this one does go through a critical speed somewhere around 500 RPM where it wants to dance all over the place but when running at around 1,400 RPM, it's pretty well behaved.  Once I have the generator and controls redone, I'll set the speed according to the manual to get the correct voltage.  I think it will end up around 1200-1400 somewhere.

It doesn't smoke so the rings must be seating all right but I think I'll need to run it for a few hours to make sure.  I ran it about an hour today.  Next time I crank it up, it should start easier and I may try advancing the spark a bit.

24 January 2006:

I've been working on the Delco off and on since last summer and will bring you up to date.

When I cleaned out the garage in KY, I gave Frank a couple of old 6-Volt electric fuel pumps.  One of them was a newer high-volume AC pump.  The other was an older Autopulse.  I had him send the Autopulse down and I took it apart and cleaned out all the corrosion, varnish and goop then I gave it a coat of paint.  The ol' girl works like a champ and I plan to use it with this Delco.

We also got a 2-gallon gas can which I took the carrying bail off of.  I fitted a pickup tube into the pour spout cap and soldered some mounting feet on it.  Painted bright red, it will make a nice gas tank for the Delco.

During the first part of January, I tackled the control panel.  Here's how it looked when I started.


After I got started, I found that it looked worse than it actually was.  After stripping the panel down to nothing, I found that all of the relay coils were okay and the contacts were cleanable.  It looks like the relay frames were originally nickel plated but nearly all of this was gone.  I don't know of a solitary plating shop that wouldn't have either lost or destroyed some of the parts so I fell back on the 'ol redneck solution.......Aluminum paint.


The coils got dried out then sprayed with insulating varnish.  After the varnish dried, I painted 'em with black enamel.  I didn't want to get too fancy with the brass and copper parts so I just wire brushed 'tm to get a little shine then coated the non-contact areas with clear acrylic.

The wires on the back of the panel were pretty grungy but intact so I covered them with "spaghetti" to make 'em look nice.

The only part we haven't been able to fix yet is the big asbestos resistor that goes on the back of the relay panel.  This resistor is center tapped and one end is set up as a rheostat.  This resistor serves two purposes.  One purpose is to drop the 32 Volts from the generator to 6 Volts at about 2 Amps for charging the battery.  The other purpose (the rheostat end) is to limit the shunt field current of the generator.  We could get by without the battery charging but can't avoid the need for the shunt field resistance.  What I did was to order a 15 Ohm 50 
Watt resistor for the battery charging resistor and I've ordered an adjustable 5 Ohm, 50 Watt resistor for the field.  When these get here, I think it'll be about time to hookup the battery and fire it up to see where the smoke leaks out.

We got some base mount porcelain sockets and a bunch of 100 Watt 32 Volt bulbs to give the ol' girl something to do when we show it.

Frank got a new nameplate from Emil Weyerts and, after banging out a couple of dents and filling most of the rust pits, I sprayed the panel cover and put on the new nameplate.  Looks kinda nice, if I do say so myself.  Here's a couple of pics I took of it today.  


Stay tuned.  Some time in the fairly near future, I'll let 'ya know how it does.

9 February 2006:

Today, I finished up the Delco 750, 32 Volt DC, 750 Watt power plant.  This is an unusual (to me at least) plant in that it does not charge a 32 Volt bank of batteries but starts on demand.  Turn on a light or appliance and it cranks off of a 6 Volt battery then, when it's up to speed, it switches the generator to the line.  When you're finished with power, when you turn off the last light, the plant shuts down.
It took a little fiddling with the relays to get it to crank and the coil wasn't grounded but once I got those little items sorted out, it fired right up.
With only one 100 Watt bulb in the circuit, the voltage is 32 Volts.  With eight 100 Watt bulbs in the circuit, the voltage is about 26.5.  Not too shabby.
The big asbestos resistor was toast and falling apart and, since we can't locate another and aren't in the mood to make one, I got a couple of 50-Watt resistors to do the job.  One of the resistors is for dropping the voltage for charging the starting battery.  We doped out the original resistance to be 12.8 Ohms.  Since we'll keep the battery on a float charger whenever we aren't playing with the set, I got a 25 Ohm resistor which makes the charging current less than the original but it'll do fine.
The other part of the original resistor was 6.5 Ohms and was adjustable as a rheostat.  The actual resistance in series with the shunt field as measured off of the original was 3.9 Ohms.  I got a 5.0 Ohm adjustable resistor to replace it. 
Here's what the replacements look like.  The top one is the battery charging resistance and the bottom one is the field resistor.  The brackets are made from stuff out of the junk box.

I fiddled with the adjustable resistor that is in series with the shunt field of the generator and it did about what I figured it'd do.  With light loads, it sets the voltage.  When the load gets heavier, the load current is drawn through the series field and this strengthens the field to compensate the voltage for loads.
After it had run for a while, I started playing with loads.....

It's tooling right along with a 400 Watt load.
And here it is with an 800 Watt load.  The throttle was almost wide open but it was still doing it's thing.
Is this a great hobby or what?


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