Home mechanic (basic tools) · Time: 30 to 45 min (estimate, done with an oil change) (estimate)
A drain plug seals with a crush washer (a soft metal or fibre ring that squashes as you tighten) or an O-ring (a rubber ring). Once squashed, a washer does not seal as well again. A leak at the drain plug usually means an old washer, a damaged seat, a cross-threaded plug or a plug that is too loose or far too tight. On the K-Light the drain is a large "filter spring screw cap" with an O-ring that also holds the strainer screen.
Safety
- A loose drain plug can fall out and empty the engine in seconds. Do not ride with a dripping plug.
- Hot oil burns; let the engine cool enough to handle.
- Wear gloves and catch all the oil.
You need
- The correct new washer or O-ring. Match the inside and outside size and material to the old one. Copper and aluminium washers are not the same size on every bike.
- Fresh oil to refill (easiest to combine with Change the engine oil and clean the strainer).
Steps
- Clean the area round the plug and confirm the leak really starts at the plug, not from higher up. Use Trace an oil leak if in doubt.
- Place the tray and remove the plug or cap slowly.
- Remove the old washer or O-ring. Old crush washers sometimes stick to the engine; peel them off.
- Wipe the seat on the engine. Look with a torch for cracks, dents or a raised edge round the hole.
- Look at the plug threads. Flattened or shiny torn threads mean the plug or the case thread is damaged.
- Fit the new washer or O-ring. Lightly oil an O-ring.
- Start the plug by hand for several turns. It must turn easily. If it binds, stop and start again straight.
- Tighten with a torque wrench to the value in your manual. K-Light 125: filter spring screw cap 15 to 30 N·m. Check that your part is this cap before using the value.
- Refill and check the oil level.
Check your work
- After idling and a short ride, the plug area stays dry.
- The plug turned in smoothly and reached torque without a sudden give.
If it did not fix the problem
- Plug spins without tightening, or threads came out on the plug: the case thread is stripped. Do not ride. A workshop can fit a thread insert or oversize plug.
- Crack round the plug seat: the crankcase may need welding or replacement. See Assess bottom end and internal engine damage.
- Oil appears above the plug: Trace an oil leak.
Reference values (K-Light 125)
| Item | Value | PDF page |
|---|---|---|
| Filter spring screw cap (drain cap with strainer) | 15 to 30 N·m | 194 |
| Seal on the drain cap | O-ring | 53 |