Home mechanic (basic tools) ยท Time: 30 to 60 min plus a short ride (estimate) (estimate)
Oil runs down and blows back in the wind, so the wet spot is usually below and behind the real leak. This job cleans the engine, then lets the leak show itself again so you can find the highest wet point. That point is the source.
Safety
- Work on a cold engine. Degreaser on a hot exhaust can catch fire and burns skin.
- Keep degreaser and oil off the brake discs, pads and tyres. If oil reaches a brake, clean the disc and replace contaminated pads before riding.
- Do not spray water or degreaser into the air intake, electrical connectors or the exhaust outlet.
You need
- Degreaser, a brush, rags and a torch.
- Talc or foot powder spray: it turns dark where fresh oil appears.
- A piece of cardboard to slide under the bike overnight.
Steps
- Check the oil level first with Check the engine oil level. An overfilled engine pushes oil out of the breather and seals.
- Make sure it is engine oil. Engine oil is brown or black and smells like oil. Fork oil comes from the fork legs. Brake fluid is clear to yellow and feels slippery and thin. Petrol smells of fuel and dries fast. Coolant is coloured and sweet smelling.
- Put cardboard under the parked bike overnight. Mark where the drops land: front of engine, middle, or by the front sprocket.
- Clean the engine with degreaser and a brush, starting at the top. Dry it with rags.
- Dust the clean area with talc spray.
- Start the engine and idle for a few minutes, or ride a short way. Stop the engine.
- Look with a torch and mirror for the highest dark line in the powder. Common places, from top to bottom: - valve inspection caps and the head cover gasket - the joint between head and cylinder (head gasket) and between cylinder and crankcase (base gasket) - the breather hose and its clamps - the oil filler cap and dipstick seal - left and right engine cover gaskets and the clutch cable or kickstart shaft seals - the gear lever shaft seal and the front sprocket (output shaft) seal - the drain cap or plug
- Check the fastener at the leak by hand only. A loose cover screw can be snugged to the manual value. Do not crank down hard on a leak: you can strip threads or crack a cover.
- Decide the repair from where the leak starts.
Check your work
- After the repair, clean again and repeat steps 5 to 7. The powder should stay dry.
If it did not fix the problem
- Drain cap: Replace the drain plug sealing washer.
- Engine side cover: Replace an engine cover gasket.
- Behind the front sprocket: Replace the output shaft seal.
- Breather or oil mist: Check the crankcase breather.
- Head or base gasket: Oil leaking from the cylinder head or base gasket.
- No leak found but the level still falls: Oil level drops but there is no visible leak.