Check engine mounting bolts

Home mechanic (basic tools) · Time: 20 to 40 min (estimate) (estimate)

On most motorcycles the engine is bolted into the frame with long bolts through the crankcase and the frame plates (hangers). On scooters and some step-throughs the engine swings with the rear wheel and hangs on a pivot with rubber bushes. Loose bolts or worn bushes let the engine move. You feel a new vibration, hear a knock over bumps or on and off the throttle, and the chain or exhaust may start to rub. The K-Light schedule lists engine bolt torque at regular services.

Safety

• Support the bike securely on the centre stand. If you remove a mount bolt, support the engine with a jack or block first: a loose engine can drop or twist the frame.
• Never remove all mount bolts at once.

You need

• Sockets and spanners, a torque wrench and the manual values for your bike.

Steps

1. With the engine cold, find each mount: front lower, upper (near the cylinder head) and rear (behind the crankcase). Scooters: the swinging engine pivot at the front of the engine case.
2. Look for a missing nut, a bolt head that has moved out, cracked hanger plates or bright rub marks.
3. Try each nut with a spanner. Note any that turn easily.
4. Tighten loose nuts to the manual value. K-Light 125: engine front mount 45 to 50 N·m, upper mount 22 to 29 N·m, rear mount 45 to 50 N·m.
5. With the rear wheel lifted, rock the rear of the bike and watch the engine. The K-Light manual uses this check for the engine mount bushes. Visible movement at a bush means it is worn.
6. Scooter: grip the rear wheel and rock it up and down and side to side. Clunks at the engine pivot mean worn pivot bushes.
7. Check that the chain slack, exhaust mounts and gear lever have not been affected: Check exhaust mounts and heat shields.

Check your work

• All mount nuts at the correct torque and marked with a paint line so you can see if they move again.
• Vibration reduced on a test ride.

If it did not fix the problem

• Bolt keeps coming loose, or a hanger is cracked: Crack in the frame or a bracket.
• Vibration from inside the engine: New or increased engine vibration.
• Vibration at a road speed, not engine speed: Vibration at certain speeds.

Reference values (K-Light 125)