Making great progress and then “bang” – snowblower stops blowing snow. It’s a startling experience and at once you know somethings up. You are in the right place alright, I’m a mechanic and this is a common snowblower issue.
A snowblower auger should not spin freely when the auger control lever is off. A free-spinning auger is a symptom of broken shear pins. Shear pins are a fail-safe feature, designed to break when the auger hits a solid object.
In this post, you’ll learn what shear pins are, how to diagnose their failure and how to fit new ones. I’ll also point out the importance of using the correct shear pins.
What are Snowblower Shear Pins?
Shear pins are also known as shear bolts, they are metal fasteners employed to fix the auger to the auger shaft. Shear pins come in two main flavors: bolts or pins. The bolts are obviously threaded and the pin variety uses a pin and clip to fasten. Not all snowblower auger shear pins are the same.
There are many different size shear pins, both bolts, and pins.
What do Snowblower Shear Pins Do?
Shear pins as you know fasten the auger to the auger shaft. The auger shaft is powered, without the pins, the auger shaft would simply turn without turning the augers. Not much use for shifting snow.
But the shear pins have another even more important function. They are designed to shear (break) when call upon. In inertia, an object in motion carries energy. When an auger suddenly stops, that energy must be dissipated. We’ve all done it, we’ve all tried to shred a frozen newspaper or dog toy.
Other common reasons shear pins break include shoes worn out or just set too low which allows the scraper bar to collect gravel and other hard to bend debris.
Yep, you’ll be clearing the yard of rocks, one shear pin at a time.
The shear pins absorb the energy by shearing. If shear pins failed to do their job, the energy would instead be transferred into the gearbox and transmitted to the engine. Often resulting in lots of downtime and many hundreds of dollars in repairs.
How to Diagnose Broken Snowblower Shear Pins
Now you know a sheared auger pin is a good thing, otherwise, you could be fixing a gearbox or worse.
Your auger assembly has as you know a separate auger on each side, with its own shear pin. Breaking both shear pins at the same time is unusual but not impossible.
Diagnosing broken shear pins is pretty easy. The main symptom is a free-spinning auger. Go ahead a place your hand on each auger in turn, they may move slightly, that’s normal but should not be free to spin.
If you can spin it, your shear pin has sheared.
Symptoms of broken shear pins include:
- Auger spins freely
- Snowblower not blowing snow far
- One auger not moving when auger lever engaged
- Snowblower not moving snow as before
How To Fit New Snowblower Shear Pins
Fitting is one of the easiest jobs you can do on a snowblower. Frankly, I’m a little jealous, in my workshop, I only ever seem to get the really tough jobs.
Anyhow, it is super important that we disable your snowblower before working on the business end.
It’s a simple procedure, I remove the spark plug wire. But you may need to remove the carburetor plastic housing in order to access the spark plug.
Just twist and pull and set it to one side away from the plug. Not you’re all set for working safely.
Tools you’ll need
To make the job move like butter you’ll need the following tools:
Wrench set (ratcheting would be nice)
Ratchet & socket and a long extension
Hammer & punch
Replacement Shear Pins
I can’t emphasize enough how important it is to fit the correct shear pins. Sure, shear pins might look like a nut and bolt but they are chosen to suit your machine. Meaning the metal is sufficiently soft so as to shear long before kinetic energy grenade the gearbox.
Bolts are identified by their tensile strength, it is the maximum force they can withstand before fracturing.
Standard (inch) and metric (mm) measurement bolts employ different markings to identify bolt strength. Most manufacturers use metric but you can expect to see plenty of standard bolts too.
Standard bolts (imperial (inch)) use a grade number. Grade two (identified ironically by no markings at all on the bolt head) is the preferred grade bolt for shear pins. An equivalent metric bolt is marked 5.6 on the head. Both bolts have a tensile strength in the 60-75,000 pounds per square inch area.
Fitting bolts graded above a grade 2 tensile strength simply means they won’t shear until a greater force is applied. Fitting bolts you may have laying around the garage is not cool. I’d be very disappointed as that would mean I didn’t do my job very well.
Order new pins as per manufacturers specs, shear pins are not all the same. I have included many of the more common types together with the tools you may need to fit them, here on the “Snowblower maintenance tools page”.
Shear Pin replacement as follows:
Rotate the free-spinning auger to locate the auger axle pinhole. Broken pin remnants may be lodged in the axle. If so, use a hammer and punch to remove. Add a little WD40 first
Using a grease gun pump grease into the auger grease nipple and spin auger to distribute the grease Align the auger hole with the axle hole
Fit the new shear pin. (some augers may have a hole larger on one side if so ensure to fit the pin with a shoulder to the larger side). Grease the new pin before fitting.
Bolt type – Tighten shear pin (bolt) using wrench and ratchet set until it seats, then back it off. The shear pin should be free to spin.
Pin type – Fitting the pin style is easier, push pin home and fit clip
It’s important the shear bolt-type isn’t tightened to the auger too tightly, just snug them up. Overtightened shear bolts won’t allow them to shear and could cost you a gearbox or worse, an engine.
Now get out there and start moving snow!
- About the Author
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John Cunningham is an Automotive Technician and writer at Lawnmowerfixed.com.
He’s been a mechanic for over twenty-five years and shares his know-how and hands-on experience in our DIY repair guides.
Johns’s fluff-free How-to guides help homeowners fix lawnmowers, tractor mowers, chainsaws, leaf blowers, power washers, generators, snow blowers, and more.