Inspect the gear shift drum, pawl and forks

The gear lever turns a shaft. A pawl or ratchet turns the shift drum a set step. Grooves in the drum move the shift forks, and the forks slide the gears in and out of mesh. Wear or a weak spring anywhere in this chain causes missed gears, false neutrals and a lever that does not return. Most shift mechanisms need no adjustment and wear slowly, so look here only when there is a symptom.

Safety

• Drain the gearbox oil first and let the engine cool. Support the bike securely.
• Work carefully with return springs. They can snap free.
• Keep parts in order. Take photos before removing anything.

You need

• Basic hand tools and a tray for parts.
• A shop manual for the shift mechanism of your engine. Types differ: drum with pawl, drum with ratchet, cam plate and quadrant, or ball lock.
• A new side cover gasket and fresh gearbox oil.

Steps

1. Check the outside first with the cover on: Check the gear lever and shift linkage. Loose lever, bent shaft or a broken return spring show up here.
2. Drain the gearbox oil. Remove the side cover that gives access to the shift parts.
3. Find the pawl, the return spring and the detent wheel or plunger. Check that the pawl moves freely and the return spring returns it to the centre.
4. Check the pawl and its pins for rounded edges and wear.
5. Check the detent wheel or plunger. It should be sprung and move in and out of the drum notches as the drum turns. A weak spring or a worn notch lets the drum float, so the bike jumps out of gear.
6. On engines with an adjustable pawl, loosen the locknut, centre the pawl as the manual shows and tighten the locknut.
7. Inspect the drum grooves for polish, ridges or burrs.
8. Check each shift fork. Look at the fork tips for bright wear marks or a bent arm. Any visible wear on a fork is a reason to replace it.
9. Look at the gear dogs and the holes they fit into. Rounded dogs make the bike jump out of gear, usually second, under power. Replace worn parts.
10. Refit everything in the same position, with new gasket and oil.

Check your work

• The lever returns to the centre after every shift.
• Each gear engages firmly and neutral is easy to find.
• No oil leaks from the cover.

When to go to a workshop

• Worn forks, drum or gear dogs when the crankcase has to be split.
• A broken gear tooth. The mating gear on the other shaft is usually replaced as well.

If it did not fix the problem

• Assess internal gearbox faults.
• Jumps out of gear under load.