What happens if the timing chain/belt breaks?

What happens when a timing chain/belt breaks on an engine?

Are the effects the same with a diesel or petrol engine ??

Asker: Roger, 63 years old

Answer

The timing belt ensures flawless timing between the components of an internal combustion engine. The parts that are particularly important in this discussion are the piston and the valves. On the attached figure, these are P (from Piston) and V (from Valve).

The piston P is the part that goes up and down. Furthermore, the right valves V must open and close at the right times, on the one hand to get fresh combustible mixture into the combustion chamber (supply valve), and on the other hand to discharge waste gases after combustion (discharge valve).

If these valves do not open and close at the correct times, the engine will not function. But this is not the real problem, after all, one could fit a new timing belt and the thing works fine again.

If everything goes smoothly, the valves are retracted every time the piston is at the top. When the timing belt is gone, the cooperation between the valves and the piston is also completely gone. For example, it can happen that the valves V come into contact with the piston P. This usually causes disastrous damage to the engine.

There is no distinction between diesel and petrol engines.

Answered by

dr. ir. Nico Smets

Engineering Science

Free University of Brussels
Pleinlaan 2 1050 Ixelles
http://www.vub.ac.be/

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