1955 CAS 400 deisel starter motor Prest-o-lite MCK4005

Stupid story short, the starter motor locked up. Too much cranking wore out one of the drive end bushings. While I had it apart I decided I wanted to redo some previous work on it ... the right way this time.

No damage to the armature ... lucky. It ohms out and sounds right on a growler.

OK, now the long story ...

The field winding wrap was in very poor shape. Previously, several years ago I had the starter apart and wrapped electrical tape around the corners of the field coils where it had been breaking and falling off.

When installing the field winding my previous solder job to the studs was very poor. I used a propane torch and burned some of the insulation but it was not grounding out so I ran the starter like that with no problems until about two weeks ago.

I have all new bushings and field wrapping tape and now a soldering iron with a large copper slug on the end of it. I timed 15 minutes with the propane torch to get the copper slug hot enough to melt solder.

Maybe I need a larger torch or use two. I don't know if I need to get the copper slug hotter but it seemed to take a long time to get that hot.

I mounted the larger stud between 2 pieces of wood in a vice. With the soldering iron/copper, I was able to tin the top of the stud where the field winding copper bars will attach.

I cleaned and glass beaded all of the housing inside and out. I am wondering if I should leave the inside bare metal where the filed pole shoes will mount or if painting the whole inside is a bad idea.

Reason I ask is because there was a layer of crud under a couple of the shoes. I'd like to know if it makes any difference if the shoes are not electrically in contact with the case of the starter motor.

I know the pole shoes have to be insulated from the field windings but is it ok if they are insulated from the case by a layer of paint ? Do the shoes need to be gounded better than just though the mounting screws ?

Also if anyone has any tips for a basic newbie doing soldering this way, I could sue some help. Last time I used a soldering iron yo heat with a torch, was in highschool metal working class. Mucho years ago. Have done lots of smaller electrical wire soldering with an electric soldering gun and small soldering pencils, so I know when solder is flowing etc.

Your starter is somewhat of a hens tooth. Find your local
starter alternator shop, and see what they have to offer.
Remember the flange that bolts the fly wheel housing Is
separate from the winding housing. It might mean just a
matter of finding another housing. CMSome of these boys
don?t always throw all their parts away

I'm in too deep to give up and start looking for a replacement. Back when this first acted up several years ago, nobody had any parts except some small parts.

I've recently gotten everything I can from those that had anything. Hoping to do a proper rebuild at this time. I have all 8 new brushes, all 3 new bushings and new wrapping tape to recover the field coils. I have successfully tinned the studs for the two pairs of filed coils using a copper soldering iron I heated for 15 minutes to get it hot enough.

An adjustable hand reamer is due to arrive today so I can re-size one of the bushings that shrunk a little going into the nose of the drive housing. Everything is clean and ready to go.

I was able to find one person who actually addressed my last remaining question ... "do I need to leave the housing unpainted on the inside where the field coil pole shoes go?". He suggested yes leave it bare and give it a thin coat of oil in lieu of conductive paint to help maintain the magnetic field connection between the shoes and the housing.

I'm thinking I'll sue some dielectric grease instead of oil. What say you MC ?

Afetr much research and head scratching, the original PREST-O-LITE MCK4005 starter is back on the engine and doing it's job and better than ever.

I ended up soldering the field coils to the stud terminals using a Harbor Freight 240v spot welder. I knew it wouldn't have enough power to spot weld the copper together. I took a gamble that it would at least heat things up enough to solder them.

The gamble paid off. The copper stud and coils heated up in seconds. AMAZING ! The solver bearing solder flowed easily into the joint. As a precaution I was wearing my welding hood and it did spark a couple of times so I'm glad I did.

If anyone else tries this with a spot welder you need to make sure the electrodes are TIGHT onto the pieces you are heating up. Otherwise a spark can occur which I'm sure would hurt a lot. The self darkening welding helmet saved my eyes from getting exposed to the bright spark at least twice while soldering these two joints.

One other thing I had to do was make a screwdriver that I could turn with a wrench. The field coil pole shoes needed to be pushed outward by a shoe spreader I also had to make. The shoe spreader was basically a 3/8" coupler nut and two bolts. I rounded the tops of the bolts so they would center in the pole shoe bolt holes. Left it tightly in place to keep the can from deforming in the vice.

With the shoe spreader in place I put the starter and screwdriver in a vice. Then I was able to apply enough force with a 1" open end wrench to really tighten the field pole shoe screws. I discovered that these screws have a different taper than standard countersunk screws. I believe the heads are supposed to acts as a type of taper lock, if you can get them tight enough.

Here are some photographs of the shoes spreader, screwdriver, and vice. The finished MCK4005 weighs 79 pounds and is 18" long. It now has 4 pairs of new brushes, 3 new bushings, a new felt oiling wick, a new felt end cushion, all 4 field coils have new wrapping and it has a whole bunch of new 10/32 socket head screws of various lengths and lock-washers throughout.

One detour had me repairing the wire lead to the solenoid coil winding. I wanted to replace the contact studs inside it but could not find duplicate studs. Tried grinding one down to match the original shape but it removed the anti-corrosion plating.

Decided to not try to learn how to re-plate them after grinding. Instead I made do with the old contacts after cleaning and repairing some damaged threads on the stud portions. I was able to retain the original Autolite solenoid that according to specifications for the starter motor, has up to 750 AMPS going through it when the starter is cranking the engine over.

So far the old 241 cubic inch 4-cylinder CASE Diesel engine has fired right up immediately a number of times in the past week. No starting fluid needed anymore. We'll see how it does in the Winter but for now I am very happy. Finally was able to get some more work out of it to clear out some big downed pine trees with the front end loader.

Next I tackle the 6' rotary mower attachment. It has done lot of field work for me keeping the weeds down and tree growth to a minimum. Through the years I've owned it, It has gotten worn out to the point the blades were starting to cut through the deck in various places. Lot's of welding needed to fix that as well as the gearbox and pivots that all need work. I'll be back asking about it when I get into that job.

More photographs of the individual pieces of the starter motor are available in case anyone wants to see any. Let me know and I'll post them.

I like your screwdriver.

Thanks Shinnery. It was one of the old wheel bolts. I cut it short and ground the flat screwdriver tip into it. The last field pole shoe screw I tightened was in pretty bad shape. The slot did not go all the way across. My screwdriver broke just as I got it tight enough ... I hope.

If I can find some new screws, I'll probably try it again with a harder piece of steel to make the screwdriver from.

The reason the starter locked up on me was because all 4 of these screws had loosened a little and the center bushing was worn out.