Interference Or Non Interference Engine – What Is The Real Difference

Interference Or Non Interference Engine - What Is The Real Difference
Interference Or Non Interference Engine - What Is The Real Difference

The term Interference or Non Interference engine gets thrown around a lot, and is really quite important.

Most people should know if their timing belt or chain has ever been replaced.

The timing belt or chain must turn the crankshaft exactly two revolutions for every one revolution of the camshaft.

Timing Belt Function Illustration
Timing Belt Function Illustration

So, When the camshaft turns it opens and closes the valves. Also, They are both driven by timing belts or chains.

Interference Or Non Interference Engine

  • Consequently, In an interference engine, if a timing belt breaks the engine might be severely damaged.
  • A non interference engine “Also Known As A Free-Running Engine” will stall if a timing belt breaks; but further damage might be limited.

When the camshaft turns it opens and closes the valves. The valve has to close and open at the exact moment when related to the movement of the pistons. Therefore, if that timing is off, everything else will be off kilter. This can also cause starting problems because the timing of all the individual components will all be disrupted.

Interference Or Non Interference – Why Could You Have Damage

Interference Or Non Interference Engine - What Is The Real Difference
Damage From Pistons Hitting Valves

Interference

Consequently, With an interference engine, valves that are fully open will be hit by the piston on the way up.

Non Interference

With a non interference engine “Also Known As A Free-Running Engine”; there is still some clearance between fully open valves and a piston in the top position.

So, Is One Design Better Than The Other

Timing Belt
Timing Belt

Advantages Of Interference Engines

Many automakers prefer using interference engines, simply because the design offers an improved compression ratio. So, As you may already know, compression ratio is the ratio of the volume of an engine’s combustion chamber. Also, By filling the engine with more combustion, it allows for increased performance and fuel efficiency.

Disadvantages Of Interference Engines

Consequently, By design, interference engines are susceptible to critical failure in the event of a timing belt failure. So, If the timing belt snaps, the pistons will smash into the valves, causing serious (and costly) engine damage. But, If the timing belt on a non interference engine breaks, the pistons won’t make contact with the valves; thus, there’s little risk of catastrophic engine damage.

Timing Chain Set Up
Timing Chain Set Up

Conclusion

When it comes to automotive maintenance schedules, they exist for good reason. So, Oil, spark plugs and most of all, timing belts should always be changes at certain times. Because, Letting them go into “borrowed time” could lead to auto repairs that outweigh the value of the vehicle. The risk highly depends on whether your engine is an interference engine or not.

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