A timing belt, timing chain or cambelt is a part of an internal combustion engine that synchronizes the rotation of the crankshaft and the camshaft(s) so that the engine's valves open and close at the proper times during each cylinder's intake and exhaust strokes. In an engine, the timing belt or chain is also critical to preventing the piston from striking the valves. A timing belt is usually a toothed belt—a drive belt with teeth on the inside surface. A timing chain is a roller chain.
Timing belts must be replaced at the manufacturer's recommended distance and/or periods. Failure to replace the belt can result in complete breakdown or catastrophic engine failure. The owner's manual maintenance schedule is the source of timing belt replacement intervals, typically every 30,000 to 50,000 miles (50,000 to 80,000 km). It is common to replace the timing belt tensioner at the same time as the belt is replaced. On some engines where the coolant pump is run by the timing belt, the coolant pump is also typically replaced.
The usual failure modes of timing belts are either stripped teeth (which leaves a smooth section of the belt where the drive cog will slip) or delamination and unravelling of the fibre cores. Breakage of the belt, because of the nature of the high tensile fibres, is uncommon. Often overlooked, debris and dirt that mix with oil and grease can slowly wear at the belt and materials advancing the wear process, causing premature belt failure. Correct belt tension is critical - too loose and the belt will whip, too tight and it will whine and put excess strain on the bearings of the cogs. In either case, belt life will be drastically shortened. Aside from the belt itself, also common is a failure of the tensioner, and/or the various gear and idler bearings, causing the belt to derail.
When an automotive timing belt is replaced, care must be taken to ensure that the valve and piston movements are correctly synchronized. Failure to synchronize correctly can lead to problems with valve timing, and this in turn, in extremes, can cause collision between valves and pistons in interference engines.
Questions and Answers
What does a Cambelt do?
A cambelt or timing belt or timing chain is a part of an internal combustion engine that synchronizes the rotation of the crankshaft and the camshaft(s) so that the engine's valves open and close at the proper times during each cylinder's intake and exhaust strokes.
What happens if Cambelt breaks while driving?
If the cambelt snaps, then many problems can occur like:
- Bent valves (most common).
- Cylinder head or camshaft damage.
- Piston and cylinder wall damage.