Many snow blowers have shear pins that break off when you hit something hard to protect the motor and drive mechanism from serious damage.
It can happen when you hit a chunk of ice that was kicked into snow at the end of your driveway by a snow plow or if you happen to hit something harder like the edge of the curb, a good sized rock or something metal like a water or sewer service pipe sometimes found near the edge of your property.
The shear pins or bolts will most likely be located on the horizontal shaft that the blades are welded to.
You will probably have two to four on each side and they are best replaced in sets.
When the shear bolts break you will definitely know it. The blades will stop turning and may spin freely once you have turned the motor off and inspect the blades. It will also probably sound like you just killed your snow blower and more then likely the engine will either die or the rpm will change.
When you hit something hard enough to break the shear bolts you are also likely to have some blade damage which may or may not be fixable.
Although the blades on your snow blower do not need to be in perfect shape and balance like a lawn mowers blade if they are bent you will increase wear on other internal parts and reduce their life.
Once you find that you need to replace the shear bolts you will most likely have to order them from the manufacturer or from a local repair shop. Don’t expect that your big box dealer will carry these extra parts but if they do they will probably be for a newer model.
Whatever you do you do not want to replace the shear bolts with standard bolts. If you do this you might as well order a new snow blower because the next time you hit something you will do some serious damage to parts that are too expensive to justify replacing.
Once you have the new bolts you should also find a spec sheet that gives you some type of exploded view and the proper torque for the bolts.
As always you want to remove the spark plug wire while you are working to make sure there is no possibility of the engine starting. It only takes a couple seconds so do it.
Many shear bolts use a nylon locking nut but others will require locktight to be added to the threads. Again you can ask when you make the purchase or find a spec sheet.
To remove the old shear bolt you may need to use a hammer and punch. This can be difficult if you can not gain good access to the parts. If your shear bolts are bent beyond the ability of removing with a hammer and punch you will probably need to take it to a repair center.
Shear Pin Bolts usually come in two standard widths of 1/4″ or 5/16ths of an inch but there can be some subtle differences so make sure that you buy a set that your manufacturer says will fit your snow blower.
From the images in this howto you can see there are many different types and some are steel while others are brass.
It is important you get the type you need and don’t just throw any set in that your store may have or the shear lines in the bolt may not line up and it would be just as bad as installing a solid bolt.
Final Note
If your engine runs but your blades do not turn then you may have other damage if you find your shear bolts are still in place. You may have a broken or lose belt, or disc clutch or gears.
The most important part is the engine and if that runs well then the rest of the snow blower can be serviced for less then the cost of a new one.