Custom Pinion Gear Replacements

Making patterns for casting a new pinion gear.

| March 2006

Have you ever been out on a sunny day, the steam is up on your engine, you're lined into the belt, the block is set, and you see an older gentleman looking over your engine like a jeweler in a penny-ante pawnshop? You try as hard as you can not to let him distract you, because what can mess up a perfect day like this? After he has opened the smokebox door he walks around your engine several times. With much deliberation he finally steps up to you, sucks the saliva out of his top dentures and says, "Well sonny, you got yourself a nice engine, but she's shot in the gearing."

Well, he is probably right, but then show me a piece of old farm machinery that is almost 100 years old without a little wear and tear. Nevertheless, what do you do about it?

There are many things that you can do, one of which is smile and agree with him, and hope that you out live him so you don't hear that kind of stuff anymore. But this article is for those of you who want to repair the gearing on your engine. Keep in mind this is only one of several gear solutions. It is meant to give you some ideas and hopefully help in some small way. The information is based on my triumphs and tragedies, none of which is etched in stone. I have to say the best time to address the gearing is when you are doing a complete restoration of the engine, because you have the engine torn apart anyway. But if your intent is to just repair gearing then any time is fine. I probably don't have to tell you that no matter when you do it, it's work!


The gearing that generally shows the greatest amount of wear would be the pinions gears. Most all transmission of power is transferred through a pinion gear. They are smaller gears, and over the years have made a lot more revolutions than their counterparts. There are other reasons why they have more wear on them, none of which are important to this article. They can show plenty of wear, causing any old codger to call you out on them. This is what I will address in this article, and how to replace them.

My engine is a 22 HP Wood Bros. It was a complete restoration, and the hind wheels had to be removed to get to the pinion gears and differential. The hind wheels are a little wider than most engines. Taking them off and moving them around wasn't too bad, but if you can get help, do it.

To get to the crank pinion, the flywheel had to come off, along with the clutch. Because of the flanges on the crank pinion, the bearing caps on the crank journals had to be loosened enough to raise the flywheel end of the crankshaft. This would allow enough room to slide the crank pinion with its flanges out over the intermediate gear and off the end of the crankshaft.