Interference Or Non-Interference? That Is The Question

There are basically two types of automobile engines: interference and non-interference and it is important that you understand which type your car uses.

Interference refers to the spatial relationship between the valves and pistons. In an non-interference engine the valves and pistons never occupy the same space. Conversely, in an interference engine the valves and pistons cross the same path, but at different times. It is the job of the timing belt to ensure that they never occupy the same space at the same time.

The timing belt 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.

Interference Engines

The interference engine creates higher compression ratios (read more power) and greater engine efficiency by allowing for a longer valve stroke and a smaller combustion chamber. In order to achieve this golden combination of more power and greater efficiency, the valves and pistons in an interference engine are required to cross the same path. The only problem with this design is that there is potential for the valves to collide with the pistons should the timing belt fail. This almost always results in a catastrophic engine failure.

Non-Interference Engines

A non-interference engine is one that has enough camshaft lift to open the valve and allow the charge of air and fuel into the combustion chamber but does not open so far into the chamber that a broken timing chain or belt would cause the valve and moving piston to collide when the camshaft stops. In non-interference engines the valves and pistons never occupy the same space, thus avoiding internal damage should the timing belt or chain fail.

So, How Can You Tell

Good question, and not an easy one to answer. Your best bet is to ask your dealer or your mechanic. You might also consult this list.

Regardless, which type of engine your car has, it is important to ensure proper maintenance of your timing belt. If your timing belt fails in an interference engine, you are going to do some serious damage. If the timing belt fails in a non-interference engine you may not cause catastrophic damage, but you will likely find yourself stranded.


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