Tighten drain and filter bolts without stripping them

Drain and filter bolts screw into soft aluminium. Many are over-tightened, so they become very hard to undo, and a stripped thread is a bad repair. On many bikes there is not enough metal around the hole for a thread repair kit.

Safety

• Hot oil burns. Let the engine cool a little.
• Use a socket that fits well. A rounded bolt head is hard to undo.

Before you remove it

• Check that you have the correct bolt. On some engines with a side drain bolt there is a gearshift spring bolt nearby. Do not remove the gearshift spring bolt. Putting it back means taking the engine out of the frame. The manual shows which is which.
• Some engines have two drain bolts. Drain both if the manual says so.
• Look at the plug. Some carry a magnet for steel particles. Some plugs have an Allen socket head with a flange. Depending on the design these can be strong or weak, so use a good-fitting key and do not over-tighten.

Steps to refit

1. Clean the plug and the hole. Fit a new washer or O-ring.
2. Look up the tightening torque in the manual. Use a torque wrench.
3. If the manual has no torque for the filter bolt, measure the bolt size and use a standard torque chart for that size.
4. Tighten to the value. Do not add extra.
5. A bolt that is stuck from over-tightening may need a reinforced socket. A stripped hole needs a larger bolt, an expanding plug or an insert, and may need a workshop.

Check your work

• No oil seeps after the engine has run.
• The bolt did not turn past the torque value.

If it did not fix the problem

• Oil leaking from the drain plug.
• Drain plug or oil filter bolt turns but will not tighten.
• Replace the drain plug sealing washer.