Transmission, clutch and final drive
This domain tests how engine torque reaches the wheel: primary drive, clutch, gearbox and final drive. Expect clutch adjustment, chain maintenance, sprocket wear and gear selection faults.
Core rules
- Wet multiplate clutch: friction and steel plates alternate in oil. Free play at the lever is set cold; too little causes slip, too much causes drag and hard gear selection.
- A clutch that slips under load raises engine speed without road speed. A clutch that drags creeps in gear with the lever held.
- Constant-mesh gearbox: gears stay engaged; shift forks move dogs. Bent forks or a worn shift drum cause jumping out of gear.
- Final drive chain: measure slack at the tightest point, adjust at the rear axle, keep sprockets aligned. O-ring chains need O-ring-safe lubricant.
- A chain too tight destroys the countershaft bearing and shock-loads the gearbox; too loose risks derailment.
- Sprocket wear shows hooked teeth. Replace chain and sprockets as a set.
Worked example
A motorcycle has 45 mm chain slack; specification is 25–35 mm. With the bike on its side stand and no load, the chain is adjusted at the tightest point. Loosen the axle nut, turn both adjusters equally, keep the wheel aligned with the swingarm marks or a straightedge, set 30 mm, then torque the axle and recheck. Reasoning: equal adjusters preserve alignment and prevent uneven sprocket wear.
Traps
Adjusting the clutch at the lever only when the pushrod is wrong; over-tightening the chain; fitting a new chain to worn sprockets; using ordinary grease on O-rings; ignoring a leaking countershaft seal.