Custom Pinion Gear Replacements

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Left: This is the crank pinion behind the clutch.
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Above: View of the pinion gear on the differential side.
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Far left (above): Blank castings received back from the foundry and ready for machining.
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Far left (below): The castings after being machined and placed on the engine.
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Below: The mating gear rode on the pinion on the back end.
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Left: The finished pinion placed on the differential side of the engine.
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Left: Three parts of the crank pinion; three parts are needed to make this pinion due to the flanges on either side of the gear. Below: A gear pattern made out of foam (left) and one out of wood (right).
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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

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.

Once the pinion gears were out and off the engine, the hard work
was over. The two pinions at the ends of the counter shaft are the
ones I will address first, because these gears are the simplest to
correct. The objective is to use the gears that were taken off the
engine and use them as patterns for new ones. Now keep in mind that
you can do this with the smaller pinion gears, but you can’t do
this with the larger bull gears. Cast iron shrinks 1/8-inch per
foot and the shrinkage for the bull gears would be too much. The
problem is that you would lose the proper mesh between the pinion
gear and the bull gear. The bull gear would be a different animal.
To replace them, a free pattern would have to be made using a
shrink rule. However, most pinion gears are less than one foot in
diameter and the shrinkage would be somewhat minimal. So using them
as patterns is doable.

The first thing these gears need is a good cleaning – they have
to be free of grease. I cleaned my gears with a wire cup brush and
a 4-inch grinder. You can use a sand blaster if you have one. It
will be a lot easier, but the wire brush works fine.

You’ll use automotive body putty to reshape the gears, and the
putty has to stick to the teeth that you are going to build up. The
cleaner the gear, the better, but the main thing is to get the
rust, dust and grease off. Each tooth will have to be brought back
to its original shape before the gear can be used as a pattern. You
might be wondering how you can get the original shape of the tooth
back. Depending on where the mating gear rode on the pinion, the
original shape of the tooth should be either out at the face of the
pinion gear or at the hind end.

The photo above shows what is called a tin cut. A tin cut
matches the shape of the front of one tooth and the backside of the
adjoining tooth. This is important to have, and important to make.
You will be using this tin cut to pull between the gear teeth. This
will help you shape the body putty as you are building up the
teeth. This is important because it will eliminate a lot of sanding
and filing. Remember, it is easier to take the body putty off and
shape the tooth than it is to shape the tooth after it has been

In my case, I plugged the gear’s bore. I did this with wood I
turned on a lathe, then stuck in the bore, covering the ends with
body putty. Once you have the pinion back on the engine, assemble
the adjoining gear and turn both gears by hand, one full revolution
of the larger gear in both directions slowly. If there is any
interference it will show up at this time. If there is, you will
have to die grind clearance on the high spots of the new gear


Now it is time to address the crank pinion, and as Art Carney
would say, “Hello crank pinion.” The same method can’t be used for
this gear because of the flanges on either side of the gear. This
gear has to be made in three parts: The two wooden flanges and the
wooden gear body. The final gear body had to be made from foam
because the foundry I was dealing with couldn’t draw a wood body
from the core sand. The main reason was they were using an oil sand
core with a cereal binder. I think if they would have gone to an
air-set, and waited until it turned somewhat plastic before they
pulled the gear body, a wooden gear body would have drawn from the
core. The foundry I was dealing with didn’t have air-set, which is
why I had to make the gear body out of foam. In all fairness, the
wooden gear body didn’t have any draft so it would have been a hard
draw anyway. Nonetheless, I found another foundry that embossed the
foam gear in a tapered block of air-set core sand as shown (Figure

Once the foam gear body was embossed in a tapered block of
air-set sand, the block of sand was placed upside down with the
taper up. The wooden flange pattern clutch side was centered over
the foam gear body. Then the drag flask was set over all and rammed
with molding sand and struck off so when the drag flask was turned
over, it would lay flat. Now the drag flask was upright (Figure 1).
At this point the engine side of the wooden flange pattern was
centered over the foam gear body. Then the cope flask was set over
the drag flask (Figure 1) and the cope half was rammed with molding

The process is reversed to retrieve the wooden flange patterns
out of the mold. Gates and runner are cut in at this time. The
tapered air-set core with the foam gear body is placed back into
the drag. Both flasks are placed back together at the parting line
and poured off. The foam gear will rapidly burn up when it comes in
contact with hot iron. The end result is a new pinion gear on the
end of the crankshaft.

These gears were poured with gray iron known in the foundry as
C-30. This means it is a gray iron or cast iron with a 30,000-pound
tensile strength. It has good machine-ability and good strength.
This is a good mix for the pinion gear over the bull gear and a
good mix for the crank pinion if you are just going to run your
engine around the fairgrounds. But for you plow jockeys, I would
recommend the crank pinion to be made out of something a little
harder, maybe adding a little chrome to the melt. A good foundry
man can help you with your mix to give you the properties you are
looking for.

Well that is all I have for you fellows in Steam Engine Land.
Until we talk again about triumphs, tragedies and pitfalls,
remember to keep your steam and water up, your hand on the
throttle, your eye on the gauge and Jesus Christ close to your

Contact steam enthusiast Mike Murphy at 7115 W. Bleck
Road, Michigan City, IN 46360.

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