Timing Woes

OF all the belts that run on the engine the most important belt is with no doubt the timing belt. A lot of us never worry about it until it breaks.

Perhaps most of us do not even know what it is because it’s always hidden behind the timing cover . . . do some preventive maintenance and you will have continued driving pleasure.

The simplest way to explain “timing” is that it is the relationship between the crankshaft and the camshaft. The camshaft spins twice for every crankshaft spin. As the crankshaft moves the pistons, the camshaft opens and closes the valves. Timing controls the movement of the pistons and the valves. The opening and closing of the valves has to happen exactly at the right time or the engine will not run properly if it runs at all because it won’t be in sync, it’s like a choir that’s singing in a discordant manner.

For us to understand the importance of timing, we have to understand that for the engine to work, valves have to open and close to let in air and out, the camshaft or camshafts in the case of a DOHC engine do the opening of the valves. The crankshaft drives the pistons up and down to compress the air-fuel mixture for ignition. The piston movement has to be in harmony with the opening and closing of the valves. The timing belt is the one that makes these two components work in harmony . . . without it there’s chaos in the engine.

An engine can have either a timing belt or a timing chain. Both perform the same function and the only difference is in the materials used and the durability of such materials. Timing belts need replacement sooner than timing chains. Timing belts are quieter than timing chains and run smoothly with no noise. They do not last as long as timing chains though, most manufacturers recommend timing belt change at every 100 000km. Timing chains sometimes last the entire life of the car.

Timing chains are more or less the same as bicycle chains but they do not operate in a quiet fashion like the timing belts, they do however, last way longer than timing belts as I have mentioned. While they may last the entire lifetime of the car, they also do wear out and start making noise, sometimes chain guides break and the chain eat away timing covers. Engines with timing chains are more complicated and require use of the correct oil every time or timing chain system fails prematurely.

Having learnt what the timing belt does, it is important to know that there’s nothing good that comes out if the timing belt breaks. To explain what happens in the event of the timing belt snapping, we would also need to understand two types of engines — interference and non-interference engines.

With interference engines, the valves occupy the same space as the pistons but not occupy that same space at the same time, so much to say that at TDC the valves are fully closed so that they don’t collide with the pistons. With such engines, in the event that the timing belt snaps, valves and pistons collide at high speed and as I always say . . . a catastrophic event will occur. Sometimes the whole engine may need to be replaced and sometimes one may be lucky enough to have cylinder head damage only.

By contrast, in a non-interference engine the pistons do not occupy the same space as the valves and with such engines, there’s no engine damage if the timing belt snaps. It is just a matter of replacing the belt and you are back on the road. Some 70% of the vehicles made in decades past are interference engines though, which is why you need to mindful of when to replace your timing belt.

When a timing belt snaps, the valves and the pistons in an interference engine collide and usually the outcome is bent valves, camshaft damage, con-rod damage, cylinder wall damage etc. The cost of a timing belt replacement is nothing compared to the cost of repairing an engine after timing belt failure. Unlike other belts that are left in the open, the timing belt hides behind a timing cover to prevent dirt and other foreign matter. It is therefore not easy to access or see hence the need to always replace as recommended by the manufacturer.

So, in retrospect timing harmonises the sub assembly parts with the cylinder head. The timing belt or chain keeps the two in sync, when it breaks the pistons and valves collide if it’s an interference engine, if it’s a non-interference engine, not so much.

It is good therefore to do that preventative maintenance and enjoy trouble free driving. Till next time . . . Happy motoring.
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