An interference engine is a type of 4-stroke

internal combustion An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder (engine), cylinder a ...

engine in which one or more

valves A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings, ...

in the fully open position extends into any area through which the

may travel. By contrast, in a non-interference engine, the piston does not travel into any area into which the valves open. Interference engines rely on timing gears, chains, or belts to prevent the piston from striking the valves by ensuring that the valves are closed when the piston is near top dead center. Interference engines are prevalent among modern production automobiles and many other four-stroke engine applications; the main advantage is that it allows engine designers to maximize the engine's

compression ratio The compression ratio is the ratio between the maximum and minimum volume during the compression stage of the power cycle in a piston or Wankel engine. A fundamental specification for such engines, it can be measured in two different ways. Th ...

. However, such engines risk major internal damage if a piston strikes a valve due to failure of

camshaft A camshaft is a shaft that contains a row of pointed cams in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition syst ...

drive belts, drive chains, or drive gears.

Timing gear failure

In interference engine designs, replacing a timing belt in regular intervals (manufacturers recommend intervals ranging from ) or repairing chain issues as soon as they are discovered is essential, as incorrect timing may result in the pistons and valves colliding and causing extensive internal engine damage. The piston will likely bend the valves, or, if a piece of valve or piston is broken off within the

cylinder A cylinder () has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infinite ...

, the broken piece may cause severe damage within the cylinder, possibly affecting the

connecting rod A connecting rod, also called a 'con rod', is the part of a reciprocating engine, piston engine which connects the piston to the crankshaft. Together with the crank (mechanism), crank, the connecting rod converts the reciprocating motion of the p ...

s. If a timing belt or chain breaks in an interference engine, mechanics check for bent valves by performing a leak-down test of each cylinder or by checking the valve gaps. A very large valve gap points to a bent valve. Repair options depend on the extent of the damage. If the pistons and cylinders are damaged, the engine must be rebuilt or replaced. If the valves are bent but there is no other damage, replacing the bent valves, rebuilding the cylinder head, and replacing the timing belt/chain components may be sufficient. Intake Valves Bent By Timing Belt Failure

Intake Valves Bent By Timing Belt Failure

References

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External links

List of vehicles with interference engines that use a timing belt
Internal combustion engine