Windmill Repair

Space Age Windmill Repair

by Kevin Moore

Could you image, about a hundred years ago, the guys in the Aermotor factory talking about the pumping Aermotor windmill. I could almost hear the conversation as I studied the deteriorated windmill in front of me.

“Hey Mac, don’t you think we should put some better grease fittings on them joints?” the old factory foreman said. “No,” the engineer replied with confidence. “The joints will last a long time with just a little grease” the engineer added. The foreman pulled the short cigar out of his mouth and pointed the cigar at the windmill pitman arm he was holding and said, “That’s all it’s ever going to get is a little grease!” The foreman tapped his cigar on the pitman pin like he was adding a drop of grease with each tap. “I’m here to tell you Mac, them hay seed farmers up in Nebraska ain’t going to be climbing up no towers, in no ice cold winter to grease up this thing. You will be lucky if it ever gets any grease, and if it does, I bet it will be goose grease,” the foreman added.

Slightly upset, the engineer took off his glasses and laid down his drafting pencil. He cleared his throat and replied, “Buddy, the pumping gear Aermotor could run twenty years without a drop of grease and the worst thing that could happen is it would get full of looseness.” The engineer put his glasses back on and said, “I bet some of those windmills are going to be around longer than you and I, so if you don’t mind, I need to get back to work designing our new oil bath model.”

“Oil bath model. Full of looseness. O’ Brother” The foreman snickered as he walked down the stairs. “Wait till the boys on the line hear about this” he chuckled to himself.

One Hundred Years Later

As I started to rebuild my “Bell Hub” Aermotor, I noticed that most of the joints had deteriorated. The pins were out of round and every hole was egg shaped by years of use. Closer examination revealed that one pin was a half-inch too short. The basic windmill was complete, but like the old guy says, “This thing is very full of looseness.”

Braze, Weld or Bondo?

I needed to return the pins to a reasonable degree of roundness. As far as the holes, I planned on inserting bushings as recommended by my friend Steve Storm. The only problem was the holes were out of round too. The bushing would not stay in place and I didn’t have room to drill out the hole and oversize the bushings.

I could use Bondo to round out the pins and braze or weld the spring holder on to the case. I’m not much of a welder, and cast-iron welding is not something I’ve ever had luck with. The thought of using Bondo on anything I own brings back bad memories of cars best forgotten.

Mixing Up a Little Steel

I decided to use a metal filled epoxy putty called “Plastic Steel® Putty” made by Devcon. It’s one of the many new epoxy products that are super strong. Devcon even advertises that you can drill and tap Devcon after it dries.


I’ve been told the key to any epoxy repair job is surface preparation. I cleaned off any oils and then sandblasted the surface. In locations where I could not sandblast, I used coarse sandpaper. I made sure that the metal had a rough profile to provide a bonding surface.

The Mold

I made up a mold from paraffin wax. I melted two blocks of paraffin together then drilled a one-inch hole in the center. I used a hot piece of flat steel as a knife to cut the model to height. I lightly heated up the pitman arm and let the bottom of the wax mold melt just a little to form fit the mold to the pitman. I made sure that I could remove the mold to add the first layer of putty and still be able to return the mold to the correct location.

Let’s Pour Some Steel

I then mixed up the two-part putty following the instructions carefully. I started by spreading the epoxy around the base of the pin. Then I slipped the mold over the base layer of epoxy. Next I added epoxy down the hole, carefully pressing it down into the hole with a flat stick. I also used a small wire to mix the epoxy into the base and remove any air pockets.

The Devcon product I was using has a working time of 30 minutes or more. I double-checked the label because they also make a 5-minute product.

It’s Round Again!

A little sanding of the edges and a filing to round off the ends and it was as good as new. I then used a little of the fast drying epoxy to set a bushing in a hole, just to make sure it would stay. As you can see in the photos, the pin is now round and the correct length.

More Than One Way to Glue a Cat

Modern epoxies are strong, easy to work with and have a multitude of applications. Steve Storm uses Devcon to hold bronze bushings in place of Babbitt. After a large earthquake here in California, a number of concrete walls had large cracks. The cracks grew with each aftershock and many people were concerned that the building would have to be torn down. The epoxy manufacturers developed an epoxy to inject into the cracks. After the initial testing, they found the only trouble was the epoxy was too strong. It made the wall ridge in the epoxy section and it would not flex as the remainder of the concrete moved in an earthquake.

Now days, you can find epoxy holding up (or down) buildings, bridges and even windmills. The key is using it correctly. It’s easier than welding and will work with most any metal or wood. Just make sure you have a clean surface that is not smooth, a large enough surface contact area and you select the right product. Above all else, follow the instructions.

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