Nuts and bolts keep coming loose

A fastener loosens again after tightening, or a nut or bolt is found missing. Engine vibration and heat cycles work fasteners loose. The cause is usually a missing or worn locking part, a wrong grade or a poor tightening method.

Is it safe to ride?

Not if the fastener is on the wheels, axles, brakes, steering, engine mounts or footpegs. Fix those first. For a panel or mirror, ride with care and fix soon.

Quick checks first

• Is a lock washer, locknut, split pin or thread locker missing?
• Is the lock washer flat and worn out? A new one is cheap.
• Is the nut or bolt scraped where the lock washer pressed on it? That shows the lock was working.
• Are the threads clean and not stripped?

Diagnose it step by step

1Does the fastener have a locking part?

• No: fit the locking part the manual shows. Types: spring, wave, toothed or tab washers, nylon or metal collar locknuts, castle nut with pin, thread locker or safety wire.
• Yes: go to step 2.

2Is the locking part worn, bent or old?

• Yes: replace it. Locknuts can be reused several times. Tab washers and key nuts must be renewed after bending.
• No: go to step 3.

3Are the threads damaged?

• Yes: clean them, or replace the bolt or have the thread repaired: Identify bolt strength and thread.
• No: go to step 4.

4Is the bolt the correct grade, length and size?

• No: fit the correct one. A weak bolt will stretch and loosen.
• Yes: tighten to the torque in your manual using a torque wrench: Use a torque wrench.

5Axle or castle nut?

• Fit a new cotter pin: Fit a cotter pin.

Tightening tip

After a bolt is fully tight, a sharp tap on the end of the spanner that turns it two or three degrees can help it hold better than ordinary tightening. This adds little tightening force, so do not use it in place of the right torque.

Causes, most likely first