What is a shear pin?

What in the world is that?
What in the world is that?
MTD Shear Pin



Well, that’s just crazy!

As insane as it may sound, some parts are actually made to break. Not in the best case scenario, of course. But in the worst case scenario, which is usually the common case scenario.

Actually, it’s not as strange as it sounds when you think about it. Airbags in your car, the bumper on the front and back of your very same car. The breaker in your fuse box is another example.

See, sometimes the worst is just going to happen. It’s life, and until we can come up with a globe sized roll of bubble wrap, its just going to keep on happening. So, when we anticipate the high probability of something going wrong, like a part breaking; we can make a choice: the expensive part or the inexpensive part.

That’s where the noble little shear pin comes in. That little bugger comes in lots of different sizes and shapes. It’s normally pretty small and you won’t see it unless you’re taking the flywheel off of your engine. Its known by many names…shear pin, keyway….um….keyw- OK, maybe not so many names; but its a pretty important part for your equipment, and here’s why.

Time to get all scientificy.

When you boil it down, the majority of your equipment is designed to do two things: break something and/or remove the debris. When we’re talking about breaking something (smashing, slashing, cutting, mulching, trimming) we’re talking about speed + force over molecular cohesion.

Bill Nye, the science guy tells me that when the quick thing (lawn mower blade) hits the stationary thing (tree root), somethings going to break. The force of inertia has to be spent somewhere! And that’s when we get the whole breakage thing.

MTD Shear Pin Set
MTD Shear Pin Set

That makes cents.

The shear pin is designed to give all that force something to break. It sacrifices itself for the good of the machine, and your pocket book cuz you gotta replace something when it breaks. Better the shear pin than something bigger, more expensive and harder to replace.

This should summarize it for you:

Shear Pin $1.95

Crankshaft: $140.00

So, there you go. Just a little bit on the break out star of the lawn mower world…the shear pin.



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Bill Brown

Bill is the head of content creation for the LawnMowerPros Blog and DIY section. He’s been in the Outdoor Power Equipment Industry for years and he’s still learning new things everyday. You can often find him creating featured articles, DIY guides, videos, graphics and much more.