Correct Cotter Pins

By: Wayne Mandeville

The true function of a simple cotter pin is often not given much consideration, and that my friend can be dangerous. Special consideration should be given to fast turning or rotating parts that use cotter pins. Let’s concentrate this tech tip on those types of applications.

If the proper size of cotter pin is not used on spinning or turning parts they can vibrate and wear themselves apart. A good example is the cotter pins used in rod bolts. It is absolutely required that the cotter pin hole be cleared of burrs and debris to allow a good tight fit. Once the diameter is established, the correct diameter cotter pin has to be secured so there is no movement of the cotter pin in the rod bolt/nut. If there is any movement at all, the continual change in engine speeds will cause the cotter pin to move around, resulting in a lot of wear, eventually failing, and potentially cause the rod nut to come loose and cause engine failure. Good quality pins are important and don’t be tempted to use cheap imports. They can break prematurely and are not as strong.

So you’re thinking I don’t perform engine overhauls so I should leave this to the rebuilder. But stop and think. Most of us do check the clearances on our mains and rod bearings and that does require us to install new cotter pins. So the replacing of cotter pins is included maintenance issues as well as major engine rebuilds. No matter what you do or have done to your Model A, a cotter pin will eventually become an issue for you to deal with. Even if you are not a mechanic and have some else to do your work be sure to advise them of the importance of good and proper sized cotter pins. Do not assume your mechanic fully understands the importance of proper sizing and application. Some of the old timers were brought up in hard times and had to use what ever was available to survive. Some old habits carry over into modern times but don’t get caught up in that situation.

I hope this will keep your Model A moving down the road and not into the repair shop.

Have a great day and let someone know that you care about them, or just give a kid a big hug, or better still give them a ride in your car. It is great to see a smile!!!!!!!!!!!!!!!

Wayne