Find out where a stuck engine is locked

When the kickstarter or starter will not move the engine, the lock can be in the engine, the gearbox, the clutch, the starter gears, the chain or the brake. This page finds which part is stuck before anything is forced. Force only breaks things.

Safety

• Do not kick or crank harder. Harder cranking breaks starter gears and shafts.
• Switch the ignition off and remove the plug cap. Remove the spark plug.
• Let a hot engine cool. A seized engine can be very hot.
• Use a long spanner on the crankshaft nut and hold the bike steady. Watch for the rear wheel moving.
• Wear eye protection when using penetrating oil.

You need

• A spanner or socket that fits the crankshaft nut or bolt (usually behind the generator cover).
• Penetrating oil.
• Time. Overnight soaking helps.

Steps

1. Put the bike in neutral and push it. If it rolls easily, the rear brake, chain, rear wheel and the gears on the output shaft are free.
2. Put the bike in top gear and try to turn the engine by pushing the bike or turning the rear wheel. If the engine turns, it is not stuck. The fault is in the kickstarter gears, or in the electric starter, its gears and starter clutch.
3. If the engine will not turn, remove the generator cover or the cover that gives access to the crankshaft nut. Fit the spanner and try to turn the crankshaft by hand.
4. If the crankshaft turns, the piston, crank, gears and clutch are probably free. The fault is in the starting gear train. See Check the kickstart mechanism or Check the starter clutch.
5. If it will not turn, pull the clutch lever in and try again. If it now turns, the fault is in the gearbox mainshaft gears.
6. If the crankshaft still will not turn, the piston is probably rusted or seized in the bore, especially after long storage or after a sudden lock-up on the road. If the crankshaft rocks a very small amount, the clutch plates may be stuck. Inspect the clutch (Free clutch plates that are stuck together).
7. For a stuck piston, put penetrating oil through the plug hole. Let it soak, then work the crankshaft gently back and forth with the spanner. Add oil, wait longer and try again. Do not use a long bar with big force.
8. If it will not free, stop. Freeing a locked piston with hydraulic pressure needs valves closed, the cams or rockers out, and the head or cylinder prepared. It is a workshop job. On a two-stroke the pressure is lost as soon as the piston uncovers the ports.
9. If it frees, the engine is not safe. It probably has damage inside. Run it gently once, drain the oil and look for fine metal and grit (Inspect drained oil for clues).

Check your work

• You know whether the lock is in the brake and drive line, the starting gear train, the gearbox, the clutch, or the piston and crank.
• The plug is refitted after the check.
• Anything that was forced is not trusted without a closer look.

If it did not fix the problem

• Engine locked, cause not found: Engine has seized or locked up.
• Internal damage suspected: Assess bottom end and internal engine damage, Assess the top end (cylinder, piston, valves).