Use heat and cold to remove and fit bearings and tight parts

Metal grows when warm and shrinks when cold. Aluminium grows more than steel. Warm an aluminium case and a steel bearing falls loose. Chill the new bearing and it drops in. This needs far less force than hammering.

Safety

• Hot parts burn. Use gloves and tongs. Do not touch a part to test its heat.
• Never heat a sealed part, a part with fuel or oil in it, or a painted part near a flame.
• Keep a torch for the last resort only. Too much heat softens steel (it loses its temper) and warps cases.
• If you use a kitchen oven, take all food out first and ask the owner.

Steps

1. Start with the gentlest heat and go up only if needed. A hot air gun is a good first choice. A hair dryer is too weak.
2. Heat the whole part, not one spot, and keep the gun moving. Uneven heat can warp a casting.
3. A guide for the right heat: a drop of water on the part boils off. Aluminium cases usually release bearings at about that point. An oven lets you reach that heat slowly and evenly.
4. Tap the bearing out with a driver that sits on the outer race. See Fit seals and bearings the right way.
5. To fit, chill the new bearing in the freezer for an hour or more. Heat the case, then drop the bearing in. Work quickly.
6. If a part goes on the outside of another, heat it. If it fits inside another, chill it.
7. Only after the oven and hot air gun fail, use a propane torch. A gas welding torch destroys the part, so use it only when you are replacing the part anyway.

Other jobs where temperature matters

• Change engine oil when warm, so it drains and the dirt is mixed in.
• Oil the chain after a ride, when it is warm, so the oil soaks in.
• Check coolant in the overflow bottle when the engine is hot. Open the radiator cap only when cold.
• Check tyre pressure cold. Check valve clearance cold.
• A compression test reads most accurately on a warm engine.

Check your work

• The part is in square and flush, with no damage to the case or the bearing cage.

If it did not fix the problem

• Stuck screw or bolt: Free a stuck fastener.
• Replace a wheel bearing: Replace a wheel bearing.