Why won’t my lawn mower engine starter engage?
Engine Maintenance Check
It can be frustrating when your lawn mower or small engine starter won’t engage, but there are solutions you can take to prevent and correct starter problems. This guide should help you find out how to locate and repair common issues with starters.
The first step in diagnosing problems with lawn mower starter parts is to make sure the engine can rotate properly by disconnecting the spark plug leads, removing the spark plugs, and turning the crankshaft over slowly by hand.
Warning: Unintentional sparking can result in an electric shock or a fire. Disconnect the spark plug wire and keep away from the spark plug. Use an approved spark checker. Do not check for spark with the spark plug removed.
Also, check for dirt or debris in the starter gear shaft and apply some lithium-based grease to the shaft.
Lawn Mower Starter Gear Problems & Repair
Use the list below to diagnose problems for 12-volt starting systems. If you are testing any parts with a multimeter, you should get a reading of 12 volts or more.
NOTE: To extend the life of the starter, use short starting cycles (five seconds maximum). Wait one minute between starting cycles.
- Additional load affecting performance- belt drag, incorrect hydraulic oil, debris.
- Discharged (dead) battery, faulty electrical connection (battery circuit), corroded terminals, battery leads too long or wire diameter too small, or incorrect size battery (too small). To address these issues, check the battery and charging system for problems.
- Wrong oil viscosity for temperature expected. Use the Small Engine Oil Recommendation FAQ for info on choosing the right lubricant for your lawn mower or outdoor power products.
- Dirty or worn starter motor commutator, bearing, weak magnets, etc.
- Worn brushes or weak brush springs.
- Valve lash out of adjustment.
- Internal bearing issues
For dirty or worn parts, use our Repair Parts Look-up to find the appropriate replacements. Your local Briggs & Stratton dealer can also assist you in finding and replacing any faulty small engine parts.
- Discharged / defective battery or faulty electrical connections. To address these issues, check the battery and charging system for problems.
- Faulty parts: potentially the safety interlocks, starter motor switch (open circuit), or solenoid.
- Brushes sticking, etc
For this type of advanced repair, we recommend using a Briggs & Stratton Repair Manual for full detailed instructions on testing for faulty parts or reaching out to a Briggs & Stratton service dealer for assistance.
- Faulty or damaged battery. To address this issue, check the battery and charging system for problems.
- Incorrect rotation due to reversed motor polarity or reverse battery connections - all motors rotate counterclockwise viewed from the pinion gear. If your motor is running clockwise, try reconnecting the battery.
- Pinion gear issues - sticking due to dirty / damaged spline or damaged pinion or ring gear. Use your Briggs & Stratton manual & Illustrated Parts List to find the appropriate parts and check for dirt or damage. Clean and/or replace as necessary.
- Starter motor clutch slipping. To address this issue, disassemble the clutch, clean the base and ball bearings with carburetor cleaner and reassemble.
- Defective starter switch
- Defective solenoid
Using your Repair Manual and a digital multimeter, you can test the starter switch and/or the solenoid to ensure they are working properly. We recommend a Repair Manual for full instructions on checking each part or contacting a Briggs & Stratton dealer for repair help.