Delco 750

[Bob Bohrer]

I have a Delco 750 doing a full tear down rebuild.
1. Looking back in previous posts I can't find anything about the journal bearing supporting the generator end of the crank shaft. In my unit there is a lot of oil in the windings of the generator section. Should there be an oil seal on the journal bearing at the armature end of the crank? The Journal bearing is not excessively loose, that is with the rotor off the crank shaft I can feel no side play in the bearing. The bearing looks like it is cast directly into the crank case. If the bearing is worn and letting oil past is there anyone who can cast and machine a replacement?
2. How much end play should there be in the crank? How is the end play set?
3. I have traced the wiring for the commutator, coils and relays. It mostly makes sense. Is there an explanation of the way this is all supposed to work? I’m just kinda guessing here.
Thanks in advance.

[Don C. Wiley]

Bob;

Are you sure your Delco-Light unit is a Model-750? It's similar to the Model-752, but it's function is a lot different.

Here is a picture of a Model-750 and you will note there is a "seperate" starter to get it running, where the Model-752 has a start winding in the generator to start it with. The 750 only used a single 6 bolt battery to operate it. When a load was applied, such as a single light, the six volt battery provided the current to pull in a relay to run the starter. The centrifugal force of the armature turning will "flip" the starter over into the grove in the flywheel. When the engine starts and the out put voltage reachea 29 volts the start relay drops out and the starter is so weighted to drop away from the flywheel. The unit generates "32" volts to run the load until all loads are disconnected then the control box resets, waiting for the next load, to start all over again.

The Model-752 uses the 16 glass cell batteries and the load has to reach a preset amount, which is usually around 8 amps and when any excess load over that is applied it will start from the start windings in the generator from the 32 volt battery. It will then run until the excess load is turned off, when it resets and shuts the engine off by disconnecting the power to the ignition coil.

These explanations are stated in the simplest form and are quite a bit more complex when trouble shooting a failed unit.

The end play in the crankshaft is zero. The double ball bearing behind the flywheel should be "clamped" tightly between the crankshaft shoulder inside the engine and the flywheel. There is a tendency when driving the flywheel tight to "pull" the flywheel away from the bearing to allow end play in the crankshaft. To avoid this, pull the flywheel up tight and then drive the tapered key in tight with a punch. You may have to grind a small grove in the flywheel nut where it tightens up next to the key, sounds complicated, but in reality it works very well.

My parts blow up doesn't show any seal on the crankshaft on the generator end. I suppose a properly fit bearing would keep most of the oil from getting into the generator end, however I've seen several with lots of oil and dirt in the generator. They aren't showing a "replceable" bearing in the crank case. If it's not too loose, I wouldn't worry about it. By the way, as bad as those shake when running at the 1250 rpm that's suggested, you won't run it enough to worry about the oil any way.

I haven't had a Model-750 apart yet, but the one in the picture is on my "to do" list, if you know how that goes ------- this year or next, or next. There is a fellow Stakr who can give you lots of information about the Model-750. He is Elden Durand, he frequents this site and would be happy to give you "first hand" information (right or wrong) about the Model-750 restoration. You can e-mail Elden off line by going to the "search" button at the top of this page and clicking on it and type in "Elden Durand". When you find his most recent post about the old generators then click on his name and select e-mail from the drop down list. He has recently changed his ISP and has a new address, so select his most recent post.

"DELCO DON" Southern Illinois

[Bob Bohrer]

Hi Don,
Well you are an inspriation, at least when I show my wife the posted pictures of your collection I can say "See my stuff anin't so bad".

Thanks for your note. Yes my unit is a 750 with the Flip Up starter.
Thanks for the info. I am just starting the cleanup and reassembly.
Bob Bohrer

[Jim Rankin]

Always a good idea to make sure any breathers are clean and totally preventing pressure buildup in the crankcase. Even with a lip seal in place a stopped up breather will sometimes cause a main to leak.

Some engines use a bearing with a slightly larger clearance outboard of a groove to collect oil and return it to the crankcase through a drain. The crankshaft may have threads to return the oil to the groove.

[Elden DuRand]

Originally Posted by Bob Bohrer

Hi Don,
Well you are an inspriation, at least when I show my wife the posted pictures of your collection I can say "See my stuff anin't so bad".

Thanks for your note. Yes my unit is a 750 with the Flip Up starter.
Thanks for the info. I am just starting the cleanup and reassembly.
Bob Bohrer

Don:

Thanks for the compliment. Your check's in the mail!

Bob:

There is no seal on the generator end of the 750. If it's really blowing a lot of oil out, check the breather. It has a one-way disc valve inside it that's supposed to let the pressure out but none back in. If the valve is clogged or stuck, you will have a very sloppy generator.

On the one I restored, it still had enough back pressure that, when I had it running at 800 Watts in a test, it drooled oil. At light loads, the leakage was less but still there. I think oil leaks are normal on Delco one-lungers.

Here's a link to my Delco 750 page:

http://www.oldengine.org/members/dur...lco/Delco.html

Hope this helps!
Take care - Elden
http://www.oldengine.org/members/durand

[Mike Schweikert]

In the service manual I have, it says that this bearing has an oil return hole back to the crankcase, and that it can leak into the generator, if it is clogged, or if the bearing is worn. It says to replace it or make sure the oil return hole in the bearing is lines up with the hole in the crankcase.....

Mike

[Bob Bohrer]

Thanks Gents,
I checked an there is a collector ring machined into the generator end of the bearing and drain hole to the crank case. Also a oil hole down from the top of the bearing boss down into the bearing from the area of the splash oiler.
Working on the crank case vent now. The original white metal vent assembly is completly broken but I do have remnants of the disk valve. It looks like it closed by gravity or a spring, that part is all missing. Is this the original of the PCV valve of today?
From the posted photos it looks like there is a pipe from the valve to the chimney to carry oil vapor to the air stream and out. Would a simple sheet metal tube with out the valve work ok here? Is it even possible to find an intact replacement PCV valve assembly?
Well thanks again for your insight and have an happy Holiday.
Bob Bohrer

[Don C. Wiley]

Bob;

You're right! It's a 1920's version of the PCV valve, however, the 1916 Model-850 through the 1947 Model-850 has the same valve, except on those, the breather smoke was pulled in with the mixer intake and was burned and sent out the exhaust pipe. The later Model-750's and 752's just vented it into the "air tube" and it was absorbed by the cylinder and around the crankcase and expelled through the flywheel.

Here is a blow up picture of an improved "crankcase breather". The one pictured doesn't have the flat metal disk, it's missing. The metal can didn't "fall apart" like the white metal ones did. The bottom section remains about the same, with a flat metal disk that had a light spring on top of it to keep it seated. When the piston was on the "up" stroke the valve would shut off air that would be drawn into the crankcase and on the down stroke the valve would open and allow the pressure built up in the crank case to escape and not blow oil out of all bearings.

If I were you I would make a suitable replacement valve to keep "dust and dirt" out of the crankcase. You don't have to vent it into the "air tube" as the original, because those later ones ended up putting the vented smoke through the engine and then out into the area where the generator was located any way.

If you search around long enough you will find an original one, but the white/potmetal ones are mostly like yours, all cracked up.

"DELCO DON" Southern Illinois

[Bob Bohrer]

Hi Don,
Thanks for the Photos and words. Yes, all I have is the seat, valve disk and scraps of pot metal. I had guessed that the tall version of the breather did carry the vapors up to the carb intake to be burned.
I don't expect this restoration to be a rush job so I will continue working on a replacement. If I cannot find the "right part" I think fabricating a duplicate of the can shown in the photo is possible.
Bob Bohrer