Fitting Shear Key

Breaking a shear-key may happen if a mower experiences a blade strike. A shear-key is pretty unassuming and inexpensive, but don't be fooled, your mower won't run without it. This video walks you through the whole process step by step.

Over View

You’ll find useful resources on this page, tips, links to tools, parts and supplies required to complete your repair.

Backfiring, no starts, pull cord snapping back violently and oil leaks are all signs that your shear-key is damaged.

If you’ve had a blade strike, then it’s very likely you need to watch this video. The good news is a shear-key only costs a few dollars.

Before working on your mower be sure to remove the plug wire to prevent accidental starting, see “Repair Safety Video”.

Tools & Parts

To nail this procedure you may need the following tools, parts and supplies.

WD40

This is first on the list for good reason, Wd solves a ton of problems. I won't work without it, because I can't. Picture links to Amazon.com

Ratchet Tool Set

Before we can do anything, we'll need tools. I've selected this set as I own some Craftsman tools and while I have worn some out, they did do a lot of work. So I expect this set will last the occasional user quite a long time.

This set carries both metric and standard sockets and that's important, because some mowers will have both type of fastener sizes. Picture links to Amazon.com

Flywheel Puller

Now this tool is a must have if you're removing the flywheel. Why would want to remove the flywheel? Sometimes the flywheel key shears, it stops your engine starting. The key is really cheap and it's easy to fix when you've got this tool. Picture links to Amazon.com

Tap & Die Set

Used to cut threads. Many flywheels are not threaded which a right pain in the jacksie, but this Gearwrench kit makes short work of threading. I especially like the ratcheting T handles. Picture links to Amazon.com

Shear-Key

OEM Briggs & Stratton shear key pack of 3, you'll only use one. I don't know why they pack 3, it shall remain a mystery. Picture links to Amazon.com

Feeler gauge

The ABN 26 blade feeler gauge set is marked in SAE and metric. You'll need this set to adjust valve lash and is useful when setting armature/coil air gap. You can also use it to gap spark plugs. Picture links to Amazon.com

Impact Wrench

I love DeWalt, they're make quality tools. This heavy duty but lightweight 1/2 inch impact wrench makes short work of stubborn bolts like flywheel nuts and rusty blade fasteners. Upto 700 ft lbs of torque on tap, I keep one in the trunk of our family car, makes a flat almost enjoyable. Picture links to Amazon.com

Drill/Screw Gun

I use a Dewalt screw gun (also a drill) in the workshop to speed up the process of removing engine covers, carburetor bolts, Armature bolts etc. It's a brushless motor and as tough as nails, I driven over it a few times - still works great! Batteries are interchangeable and so if you have a Dewalt product already you won't need the battery. Picture links to Amazon.com

Torque Wrench

Teng 1/2 Torque wrench, fantastic tool I use it every day and mine is still going strong. A torque wrench is advised for tightening components such as flywheel nuts and blades. The torque spec of these components is very important. Picture links to Amazon.com

If you are considering buying a torque wrench, definitely check out my review of Teng torque wrench.

Piston Stop Tool

Universal piston stop tool 10mm and 14mm, used to lock the crankshaft when removing and tightening the flywheel nut. Picture links to Amazon.com
John Cunningham
Auto Technician and Writer at | Website

John Cunningham is an Automotive Technician and writer on Lawnmowerfixed.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write "How to" articles that help fellow gear-heads with all aspects of mechanical repairs, from lawn mowers to classic cars.