interference engines are an engine design that has been avoided by some manufacturers for as long as technically possible. General Motors, Chrysler, etc., typically use a metal chain-type timing chain on push-rod engines (not a timing belt) to transmit torque from the engine crankshaft of the camshaft that opens the valves that allow air and fuel into the cylinder. On some new cars the fuel is admitted not through the valves but through fuel injectors in the top of the cylinder. Rather than use a steel timing chain, interference engines may use a rubber timing belt with its limited life, whereas steel timing belts typically last 150,000 to 200,000 miles or more.
Valves open further in an interference engine and protrude further into the combustion chamber than in a ‘free-running’ engine. This allows outside air at atmospheric pressure flow faster into the combustion chamber through the larger valve opening. The engine can therefore inhale more air, be a little smaller, and still create as much power while reducing its manufactured cost and also guaranteeing future repair business for its dealer.
If a rubber timing belt breaks by not being replaced soon enough, some of the valves stuck in their open position will collide with the top of the pistons, thereby breaking or irreversibly damaging one or the other or both. To make matters worse, it is not possible to measure the wear on such a rubber belt so that it could be replaced when there is some indication of imminent failure.
Failure in these belts is catastrophic, without warning. This will require a complete replacement engine. Finally, the rubber belt may have to be replaced long before 60,000 miles solely due to its age. Interference engines are like a time bomb waiting to explode unless replacing the timing belt at the recommended interval. Be aware of that guaranteed future expense before buying a new car, or especially a used car, with such an engine.
When buying a used car, supposedly with 40,000 miles for example, and determining it has a rubber timing belt, insist on a written guarantee from the seller to guarantee in writing to replace the timing belt at no charge if it fails within another 20,000 miles. After all, the vehicle may in fact already have 55,000 miles on it. If the seller will not make that guarantee, then he is admitting that the mileage is probably not accurate and by implication may well have been turned back. If the seller will not make that guarantee, consider a compromise, such as $100 maximum cost. If not acceptable, walk away and look elsewhere.
Before buying any car, especially 4-cylinder foreign cars, be aware of the unavoidable cost of $400-$800 to replace the timing belt at anywhere from 50,000 to 70,000 miles if the car has an interference type of engine. If a timing belt on an interference engine is not replaced at recommended intervals, the repair cost when the belt breaks (not gradually, but always catastrophically) could increase to $3,000 to $5,000 due to engine failure because parts have banged into each other
As you might expect we sell lots of interference motors for foreign cars in particular. We won’t give you any ”hanky-panky” about what type of engine we are selling you. There is nothing to hide. If your interests are in good used engines, we document the mileage and pre test them before putting them up for sale. If it uses a timing belt, you will be informed about how to handle replacement when you arrive at the correct mileage.
If you end up having to purchase a good used engine from us, the value is built into the foreign engines we sell, and no one can beat our customer service. Call us now @ 1-941-269-8284 and find out why this is ”where our customers send their friends”. GotEngines.com