When the starter does nothing, or the kickstarter will not move, the cause is one of four: the battery or starter circuit, the starter drive gears, the gearbox, or the engine itself. These checks separate them without taking the engine apart.
Safety
- Engine off, key out, plug lead off while you turn the engine by hand.
- Do not force a seized engine with the starter. You can burn the starter or break gears.
- Disconnect a faulty battery. Use a separate charged battery of the same voltage if you must test.
You need
- Spanner or socket to fit the nut or bolt on the end of the crankshaft (under the flywheel cover on many bikes). Check the size on your bike.
- Penetrating oil.
- A charged battery and jump leads, for the electric-start check.
- Plug spanner.
Steps
- Electric start: click only. The starter relay clicks but the starter does not turn. Check the battery is charged: Test and charge a 12 V battery. If it is charged, continue with Test the starter circuit. A bypass of the relay with a thick lead is a workshop test. It makes a large spark.
- Starter turns but the engine does not. The starter drive gears or the starter clutch is at fault: Check the starter clutch.
- Kickstarter will not move. Put the gearbox in neutral. If it has a high gear, select it and push the bike gently on its wheels. If the engine turns when pushed, the kickstart gears are at fault: Check the kickstart mechanism.
- Check by hand at the crank. Remove the plug and the flywheel cover. Put a spanner on the crank end nut. With the gearbox in neutral, turn the crank slowly. - Turns: the problem is in the gears or starter, not the engine. Go back to steps 1 to 3. - Does not turn, even by hand: the engine is stuck. Go to step 5.
- Stuck engine. The common cause is rust between the piston, rings and cylinder after long standing. Pour a little penetrating oil through the plug hole and leave it for some hours, or overnight. Turn the crank with the spanner gently, back and forth. Do not use the starter.
- If it comes free, turn it over by hand many times, with the plug out and the lead off, until it moves easily. Then check compression: Test engine compression.
- If it will not come free, or it frees but feels rough, the engine needs the top end opened: Assess the top end (cylinder, piston, valves). A worn bore will need a new piston and rings, and often boring. A four-stroke also needs the valves checked.
Check your work
- You know which of the four causes it is and have written it down.
- If the engine turns by hand, it turns freely with no tight spot. If you freed it with oil, compression is acceptable.
If it did not fix the problem
- Engine locked after running, with a bang or a squeal: Engine has seized or locked up and Assess bottom end and internal engine damage.