[BY SEAL]
24 May 2006 2006-05-23 18:01

Beginning with this article, is aseries of articles designed for you to know what goes on inside your beloved Kangoo. Hence, the title ;-). Hopefully, the articles, “translated” into plain English, are easy enough for the laymen and laywomen in us to understand.

The question of how often should we change our timing belt is something that is fervently discussed in KCM Forum. Interestingly, the Motor Trader website carries a feature article on timing belts by Chris Yap, entitled The Importance of changing a timing belt / chain.

According to that article, the timing belt is recommended to be changed every 100,000 kms or less if you have bought a used vehicle and service records are not available to you. Now, the timing belt is used to transfer the rotation of the crankshaft to the camshaft. For the auto-tech challenged like me who cannot tell the difference between the crankshaft and camshaft from the head and tail, Wikipedia is a revelation.

The camshaft is an apparatus used in piston engines to operate poppet valves. It consists of a cylindrical rod running the length of the cylinder bank with a number of oblong lobes or cams protruding from it, one for each valve. The cams force the valves open by pressing on the valve, or on some intermediate mechanism, as they rotate

The crankshaft, on the other hand, is that part of an engine which translates reciprocating linear piston motion into rotation. It typically connects to a flywheel, to reduce the pulsation characteristic of the four stroke cycle , and sometimes a torsional or vibrational damper at the opposite end, to reduce the torsion vibrations often caused along the length of the crankshaft by the cylinders furthest from the output end acting on the torsional elasticity of the metal.

The relationship between the rotation of the camshaft and the rotation of the crankshaft is of critical importance. Since the valves control the flow of fuel intake and exhaust, they must be opened and closed at the appropriate time during the stroke of the piston. For this reason, the camshaft is connected to the crankshaft
either directly, via a gear mechanism, or indirectly via a belt or chain called a timing belt or timing chain.

In a two-stroke engine that uses a camshaft, each valve is opened once for each rotation of the crankshaft; in these engines, the camshaft rotates at the same rate as the crankshaft. In a four-stroke engine, the valves are opened only half as often; thus, two full rotations of the crankshaft occur for each rotation of the camshaft.

In modern gasoline engines the overhead cam system, the camshaft is on top of the cylinder head. Some engines use one camshaft each for the intake and exhaust valves; such an arrangement is known as a double or dual overhead cam (DOHC), thus, a V engine may have 4 camshafts.