If your mower makes a clicking sound but won’t turn over, the starter motor might need testing. Learning how to test a lawn mower starter motor is a key skill that can save you time and money. This guide provides clear, step-by-step instructions to help you diagnose the problem safely and accurately.
Before you begin, always prioritize safety. Disconnect the spark plug wire to prevent any accidental engine starts. Make sure the mower is on a flat, stable surface and the engine is completely cool. Gather your basic tools: a set of wrenches, screwdrivers, a multimeter, and some safety glasses.
How To Test A Lawn Mower Starter Motor
A systematic approach is the best way to test your starter. Rushing can lead to misdiagnosis. Follow these steps in order to pinpoint whether the starter motor itself is faulty or if the problem lies elsewhere in the starting system.
First, you need to locate the starter motor. It’s typically found on the side of the engine, connected to the flywheel housing. It’s a cylindrical component with a larger gear (the bendix) that engages with the engine flywheel. You’ll see a thick red cable connected to it from the battery and often a smaller wire for the solenoid trigger.
Essential Safety Precautions And Tools
Never skip safety. A small mistake can lead to injury or further damage to your mower. These precautions are non-negotiable.
- Disconnect the battery: Always remove the negative (black) cable first, then the positive (red) cable.
- Disconnect the spark plug: This ensures the engine cannot start unexpectedly while you’re working.
- Wear safety glasses: Protect your eyes from debris and sparks.
- Work in a well-lit, ventilated area.
- Have a fire extinguisher nearby, especially when dealing with battery connections.
The basic tools you’ll need include a multimeter for electrical tests, a set of wrenches and sockets, screwdrivers, and a pair of insulated jumper cables or a dedicated starter bench tester. A service manual for your specific mower model is also incredibly helpful for torque specs and diagrams.
Initial Visual Inspection
Before any electrical tests, a thorough visual inspection can reveal obvious problems. Look for signs of damage, corrosion, or loose connections that could be the simple culprit.
- Check Battery Terminals: Look for heavy corrosion (a white or blue crusty substance). Clean terminals with a wire brush if needed.
- Inspect Wiring: Follow the cable from the battery to the starter. Look for frayed wires, cracked insulation, or connections that are loose.
- Examine the Starter Body: Look for cracks, oil saturation, or physical damage. Check that the starter is mounted securely to the engine block.
- Look at the Starter Gear (Bendix): Ensure it moves freely and isn’t clogged with grass clippings or debris. It should retract smoothly.
Testing The Lawn Mower Battery
A weak battery is the most common reason for starting failure. It can mimic a bad starter. Use your multimeter to check the battery voltage.
- Set your multimeter to DC Volts (20V range).
- Touch the red probe to the positive (+) battery terminal and the black probe to the negative (-) terminal.
- A fully charged 12-volt battery should read between 12.6 and 12.8 volts. Anything below 12.4 volts is weak and needs recharging or replacement.
- For a load test, have a helper try to start the mower while you watch the multimeter. If the voltage drops below 9.6 volts, the battery is likely bad.
Bench Testing The Starter Motor
This is the most definitive test. It removes the starter from the mower’s electrical system to check its function directly. You’ll need a fully charged battery and jumper cables.
- Disconnect the battery and spark plug wire.
- Remove the starter motor from the engine. This usually involves two or three bolts.
- Place the starter on a non-conductive surface like a wooden bench.
- Connect one jumper cable from the positive (+) battery terminal to the main terminal stud on the starter (where the thick red cable was attached).
- Briefly touch the other jumper cable from the negative (-) battery terminal to the starter motor’s metal casing.
Caution: Be prepared for the starter to spin and jump. Hold it firmly. If the starter motor spins powerfully and extends its gear, it is functioning correctly. If it does nothing, spins weakly, or makes grinding noises, it is faulty. This test confirms wheather the starter itself works when given direct power.
Testing The Starter Solenoid
The solenoid is a relay that sends high current to the starter. When you turn the key, you here a clickâthat’s the solenoid. A faulty solenoid can prevent power from reaching the starter motor.
To test it, you’ll use a multimeter set to continuity or resistance (Ohms). Locate the solenoid, usually mounted near the battery or starter. It has two large terminals and one or two small terminals.
- Disconnect all wires from the solenoid.
- Set the multimeter to the continuity setting (often symbolized by a sound wave icon).
- Place one probe on one large terminal and the other probe on the other large terminal.
- Actuate the solenoid by applying 12 volts to the small terminals (if it’s a 4-post type) or by grounding the case (if it’s a 3-post type). You can use jumper wires from the battery.
- If the solenoid is good, you will hear a click and the multimeter should show continuity (a beep or near-zero resistance) between the large terminals. No click or no continuity means a bad solenoid.
Checking For Voltage Drop And Ground Connections
Sometimes, the starter is fine but it’s not getting enough power due to poor connections. A voltage drop test identifies resistance in the circuit. This is a crucial step often overlooked.
Recconnect the battery and starter. Set your multimeter to DC Volts. Have a helper hold the ignition key in the “start” position.
- Test the positive circuit: Place the red probe on the positive battery terminal and the black probe on the starter’s main terminal stud. A reading over 0.5 volts indicates high resistance in the positive cable or connections.
- Test the ground circuit: Place the red probe on the starter motor casing and the black probe on the negative battery terminal. A reading over 0.2 volts here indicates a poor engine ground.
High voltage drop means power is being lost as heat in the wiring. Clean or replace the corroded cables and tighten all connections. A bad ground is a very common issue; ensure the ground cable from the battery is attached to clean, bare metal on the engine block.
Understanding Common Starter Motor Problems
Knowing what typically fails inside a starter helps you understand the test results. Here are the most frequent issues.
- Worn Brushes: These are carbon blocks that transfer electricity to the armature. When they wear down, contact is lost and the starter won’t spin.
- Faulty Armature: The spinning core of the motor can develop shorted windings or commutator problems, causing weak operation or no operation at all.
- Bad Solenoid (as tested above): The internal contacts can burn out, preventing current flow.
- Stuck Bendix Gear: The drive gear can jam due to dirt or lack of lubrication, preventing it from engaging the flywheel.
- Burned Out Windings: If the starter has been overloaded, the field coils inside can overheat and fail, often with a distinct burnt smell.
When To Repair Or Replace The Starter
After testing, you must decide wether to fix or replace the unit. For many DIYers, replacement is the more practical option.
Consider repair if: The starter is a high-quality model, repair kits (brushes, bushings, solenoids) are readily available, and you are comfortable with detailed disassembly. Repair is often cheaper but more time-consuming.
Consider replacement if: The starter is old, the housing is cracked, the armature is damaged, or repair kits are not available. A new or quality remanufactured starter offers a reliable, long-term solution with a warranty. Always compare the cost of a repair kit to the price of a new unit before deciding.
Final Steps And Reassembly
Once you’ve tested and resolved the issue, careful reassembly is key. Rushing this can cause new problems.
- If you replaced the starter, compare the new one to the old to ensure it’s the correct model.
- Clean the mounting surface on the engine block to ensure a good ground.
- Install the starter and tighten the bolts to the manufacturer’s specification. Over-tightening can crack the housing.
- Recconnect the main power cable and any control wires to the solenoid.
- Reconnect the battery: positive cable first, then negative.
- Finally, reconnect the spark plug wire.
Give it a test start. Listen for a strong, quick engine turnover. If the engine starts, you have successfully diagnosed and fixed the problem. If not, you may need to revisit other systems like fuel or ignition.
Frequently Asked Questions
What Are The Signs Of A Bad Starter Motor On A Lawn Mower?
The main signs include a single loud click when you turn the key with no engine movement, a whirring or spinning sound without the engine engaging (freewheeling), intermittent operation where it works sometimes and not others, and a completly silent response when turning the key (after confirming the battery is good).
Can You Test A Starter Without Removing It?
Yes, you can perform several tests without removal. You can check for voltage at the starter terminal during cranking, perform a voltage drop test, and listen for solenoid engagement. However, a bench test provides the most conclusive diagnosis of the starter motor’s internal condition.
Why Does My Starter Click But Not Engage?
A rapid clicking usually indicates a weak or dead battery. A single solid click often points to a faulty solenoid or a starter motor with internal problems, such as worn brushes or a seized armature. The click is the solenoid pulling in, but power is not reaching the starter motor to spin it.
How Much Does It Cost To Replace A Lawn Mower Starter?
Costs vary widely by brand and model. A replacement starter motor typically ranges from $50 to $150 for the part itself. If you have a professional perform the replacement, labor could add another $75 to $150. For common mower models, aftermarket starters are often affordably priced.
Is A Lawn Mower Starter Motor Repairable?
In many cases, yes. Common repairs include replacing the carbon brushes, the solenoid, or the bendix drive assembly. Repair kits are available for many popular models. However, if the armature or field coils are damaged, a full replacement is usually the better option.