Cotter Pins

What Every Model T’er should Know

Don’t ever under estimate the lowly cotter pin. Most modern equipment may not have them, but the Model T has many of them. They are there to hold you car together. A Model T can shake like a wet dog. You certainly don’t want your cars parts falling off, specially when you are out touring and having fun. Cotter Pins are cheap enough that anyone can afford to have good collection of them around in the shop.

A Cotter Pin will have a diameter. The collection above has 1/8 and 5/32 inch diameters. The Cotter Pins will also come in various lengths. A Cotter Pin will work with a castellated nut. These nuts also come in different shapes.

The bolt or shaft that corresponds to the pin and nut must have a hole drilled in it. Make sure the hole is clean and has the same diameter as the Cotter Pin. The Cotter Pin must be long enough to be wrapped over the nut and bolt end, as seen below. Advance the nut over the threads. The nut should be tight.

If the hole doesn’t line up with the nut notch, tighten the nut more rather than loosening it. Insert the Cotter Pin all the way into the hole so that the loop fits snuggly in the notch of the castle nut. Next bend over the split ends of the Cotter Pin so that one is over the nut face and the other is over the shaft. This is what a properly installed Cotter Pin should look like. Finding castle nuts is not difficult, many hardware stores will have a good selection.

Finding an appropriate bolt with a hole in it is another matter. Here is a little jig that I made for 3/8 inch bolts, to add a Cotter Pin hole. It is drilled and tapped to hold the bolt. There is a small hole corresponding to the Cotter Pin drilled perpendicular to the tapped hole.

The bolt is inserted and drilled either in a drill press or carefully by hand. You may have to experiment with a few bolts to get the hole placed at the correct height.

You have to find the right combination of how far to insert the bolt into the jig to drill the Cotter Pin hole correctly.

Otherwise, you may find that once the nut is tight the Cotter Pin can not be properly inserted. Sometimes Cotter Pins may seem like extra fuss, but you don’t want your nuts to fall off!