Remove and inspect the starter motor

The starter motor is a small DC motor bolted to the crankcase. Its brushes press on a copper commutator to pass current into the spinning armature. Worn brushes, a dirty or burnt commutator, or a shorted armature give slow cranking or no cranking. Removing the motor is often a home job; testing and repairing the inside is best done by a workshop or auto electrician.

Safety

• Key OFF. Disconnect the battery negative (−) before touching the starter cable. The K-Light 125 manual then asks you to press start to confirm that nothing turns.
• Let the engine cool. The starter often sits near the exhaust.
• Do not run the starter on the bench with jump leads unless you hold it firmly in a vice. It kicks hard.

Before you remove it

Do these checks first. A starter is often blamed for a battery or cable fault.

• Battery charged and terminals clean: Test and charge a 12 V battery.
• Full battery voltage reaches the starter terminal while cranking: Test the starter circuit.
• The engine turns freely by hand or with the kickstarter. A tight engine is not a starter fault.

What you can do at home

1. Disconnect the battery negative.
2. Remove the cable from the starter terminal.
3. Remove the starter mounting bolts and pull the motor out of the crankcase. Catch the O-ring.
4. Look at the gear on the end of the shaft: chipped or worn teeth mean the gear it drives may also be damaged.
5. Check that the shaft turns smoothly by hand.
6. Check the earth face where the motor bolts to the engine. Clean it to bare metal.

What the workshop will check

• Brush length. K-Light 125: standard 12.5 mm, service limit 8.5 mm. Replace brushes below the limit.
• Brush springs: weak springs give poor contact.
• Commutator: dirty, burnt or worn deep grooves.
• Armature: tested for open or shorted windings with a meter or growler.
• Bearings and bushes for play.
• A bench run test under load, if they have the equipment.

Ask for: the measured brush length, the state of the commutator, and whether brushes alone or a complete starter is needed. A rebuilt starter can be good value; check the warranty.

Refitting

1. Fit a new O-ring and smear it with a little oil or grease.
2. Push the motor fully into place by hand. Do not pull it in with the bolts.
3. Tighten the mounting bolts. K-Light 125: 10 to 12 N·m.
4. Fit the cable and its rubber cover. Reconnect the battery.

Check your work

• Cranking speed is normal and even.
• No grinding when the starter engages.

If it did not fix the problem

• Starter spins but the engine does not turn: Check the starter clutch.
• Grinding noise: Grinding or screeching noise when starting.

Reference values (K-Light 125)