Test And Replace Lawn Tractor Starter
Article by Mark Trotta
Like you've done so many times before, you turn the key to the right, but instead of the lawn tractor starting, all you get is a clicking sound. Before you start changing parts unnecessarily, here's a few simple tests to help determine what's wrong.
Before testing the starter, check that the battery is fully charged, and that it's the proper size for your lawn tractor. Also check for old, frayed, or faulty wiring.
A common overlooked item is the seat safety switch, sometimes called an interlock. They are usually located just underneath the seat when tilted forward.
Test Starter On Lawn Tractor
The starter doesn't have to be removed from the engine to be tested. By connecting a test wire from the positive (+) side of the battery to the terminal lug on the starter, you'll know if it's the starter itself that's bad, or another component.
All you need to do is touch the terminal with the test wire for a quick few seconds--you don't want to connect it (or the starter will stay running).
* If the starter does not turn the engine over, you have a bad starter.
* If the starter does turn the engine over, check the ignition switch, starter solenoid, and interlock.
As you turn the ignition key to the far right, the starter solenoid "energizes" the starter motor, pushing the pinion gear into the flywheel teeth. When a starter's bad, you'll likely hear a "click" sound, which is the solenoid trying to work by pulling in the armature.
Unlike a car or truck, a lawn tractor solenoid is rarely mounted on the starter. It's usually mounted somewhere close to the positive (+) side of the battery.
The starter solenoid will have either three or four threaded electrical terminals - one or two terminals are small, and one or two are big. The terminal wires attach to the battery, ignition switch, and starter.
Sometimes a solenoid will have an external ground wire terminal. A starter solenoid with three terminals will usually use the mounting ears as a ground, and a solenoid with four studs will use one of the small lugs as an "extra" ground.
Test The Starter Solenoid
To test the starter solenoid, connect a test wire from the positive (+) side of the solenoid to the terminal lug on the starter.
If the starter turns the engine over, it's likely you have a bad ignition switch.
If the starter does not turn the engine over, replace the solenoid. This is easy DIY fix.
Starter Solenoid Location
Mounting locations for starter solenoids tend to vary. On this John Deere lawn tractor, it's under the hood by the battery. On older models, it may be hidden under the seat by the battery. Some Cub Cadet models have it under the battery on the back wall.
The Stens 435-151 solenoid replaces John Deere #AM138068, Cub Cadet #725-04439, MTD #725-04439, Trombetta #812-1211-211-16, and others.
Shop: Starter Solenoid
What Causes A Starter To Fail?
A lawn tractor starter can go bad in several ways. It can fail electrically - this is when the copper winding from the armature breaks, or when brushes break or wear out.
Starters can also fail mechanically. Through age and use, the top and bottom bearings wear out. The pinion gear can also wear out. Mechanical issues such as these cause the starter to bind, and the starter will emit a clicking sound when activated.
Once you determine the starter is bad, you need to identify it to order a new one. On a Briggs-powered lawn tractor, you'll need to remove the blower housing (unless your owner's manual gives you a part number).
The John Deere lawn tractor in the pictures is powered by a Briggs & Stratton OHV Intek motor. Other brands powered by the Briggs Intek include Ariens, Bolens, Husquarvna, John Deere, Scotts, Sears, Toro, and others.
Single-cylinder Briggs engines generally have one of two types of starter - it will have either a plastic gear or a metal gear. If you're not sure by looking at it, hold a magnet to gear and see if it sticks.
Verify the tooth count on the gear, it will probably be either 14 or 16. Also note if the mounting bracket is cast aluminum or stamped steel.
14 Tooth With Metal Gear
This John Deere lawn tractor has a 14-tooth metal gear starter with a steel mounting bracket. The OEM part number is 593934, and it fits many lawn tractors, including John Deere models LA100, LA105, LA110, and LA115.
Shop: Briggs and Stratton OE Starter Motor 593934
This starter is an OEM authorized part and comes in a Briggs & Stratton box. This starter also fits other Briggs-powered lawn tractors, such as Cub Cadets, New Holland, Toro, and others. Alternative part number is 693551.
16 Tooth With Plastic Gear
If the gear is plastic and has 16 teeth, and the mounting bracket is steel, it is a Briggs part number 391423. John Deere uses part number AM122337.
Shop: Briggs and Stratton Replacement Starter Motor 391423
This brand of starter (Rare Electrical) is top-rated and includes a spare pinion gear, as the gear often wears out prematurely. NOTE: On some applications you may have to transfer the front mounting bracket from the old starter to the new starter.
On most small engines, the starter motor bolts right up to the engine crankcase. If you haven't already done so, disconnect the negative (-) battery cable from the battery. This will prevent any accidental starting during the removal/replacement process.
Disconnect the wire terminals that secure the ground wire and the positive wire to the backside of the starter.
Disconnect the wiring harness that connects to starter to the electrical system. Usually the harness is a plug-in type, where you push in on a locking tab and then pull on the harness to disconnect it.
Remove the bolts that secure the starter to the engine block and lift the starter from the engine. Although not too common these days, you may find a shim or two mounted between the starter and the engine block. If there is, note how they came off, and re-use them with the new starter.
Install New Starter
After you've cleaned off the old starter bolts, bolt the new starter to the block. The base of the starter should rest flush against the block to ensure the gear inside the starter motor seats with the gear inside the engine. Do not over-tighten the bolts.
Re-attach the ground and the positive wires to the back of the starter and plug the wire harness back in. The last step is to re-connect the negative battery cable.
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