Replace an engine cover gasket

The left cover usually hides the generator (stator and flywheel) and sometimes the starter gears. The right cover usually hides the clutch, the oil pump and, on many commuters, a centrifugal oil filter. A cover gasket can leak when it ages, when screws work loose or after a fall. Changing it means draining oil and working near parts that need exact settings, so this page is an assessment and a guide to what the workshop does.

Safety

• A leak onto the rear tyre or a hot exhaust is dangerous. Clean it off and fix it before longer rides.
• A cover cracked in a fall can lose all its oil quickly. Do not ride if oil is running, not just seeping.
• The flywheel magnet pulls hard on tools and fingers. Keep steel parts clear.

What you can check safely

1. Clean the cover and find the exact leak with Trace an oil leak.
2. Look for cracks or scrapes on the cover from a fall. A crack is a new cover, not a gasket.
3. Check each cover screw by hand with the correct screwdriver or socket. A loose screw can be snugged to the manual torque. K-Light 125: left and right crankcase cover bolts 9.8 to 11 N·m. Do not go higher; the threads are in aluminium.
4. Check seals in the cover: the kickstart shaft, gear lever shaft and clutch lever shaft. Oil coming out round a shaft is a seal, not the gasket.
5. Check the oil level. An overfilled engine pushes oil past gaskets: see Too much oil in the engine.

What the workshop does

• Drains the oil, or tilts the bike so the oil stays away from the cover being removed.
• Removes parts in the way: gear lever, kickstart lever, brake pedal, exhaust on some bikes.
• Undoes the cover screws in a cross pattern and notes which screw goes where (lengths often differ).
• Removes the old gasket without gouging the faces, using a plastic scraper.
• Checks the faces for flatness and damage. Checks dowels and O-rings.
• On the clutch side, keeps the clutch push rod and any oil-filter parts in order.
• Fits a new gasket (dry or with sealant only where the manual says).
• Tightens screws in a cross pattern in stages to the manual torque.
• Refills oil, runs the engine and checks for leaks.

What to ask for

• A new gasket of the right shape, not one cut from sheet unless the shop has the template.
• New O-rings and shaft seals if they are hard or leaking.
• The old gasket and any damaged parts, so you can see the cause.

Do not attempt at home

• Removing the flywheel or clutch to reach a seal. These need pullers and holders (K-Light special tools list flywheel puller and clutch holder).
• Using silicone in place of a gasket where the manual does not say so. Excess sealant can block oil passages.

Check your work

• Cover stays dry after a ride and a cooling cycle.
• Gear lever, kickstart and clutch work normally.

If it did not fix the problem

• Leak is higher up: Oil leaking from the cylinder head or base gasket.
• Leak is at the sprocket: Replace the output shaft seal.

Reference values (K-Light 125)