| Interference Engines Interference Engines: ........Free Useful information When buying a used car always insist on determining if thevehicle has a rubber timing-belt. Be aware that about five yearsago an International Oil Company did a follow up on 5,000 carsit had turned back after 3 year leases and traced them to theireventual private owners. All the cars had by then passed throughwholesale auction markets and likely one or more retail dealersbefore being sold to a private owner. The survey disclosed that50% of the cars had their odometers illegally turned back. When buying a used car, supposedly with 40,000 miles forexample, and determining it has a rubber timing belt, insist ona written guarantee from the seller to guarantee in writing toreplace the timing belt at no charge if it fails within another20,000 miles, a typical recommended total amount (Call anyDealer to get the recommended amount for the particular make ofvehicle). After all, the vehicle may in fact already have 55,000miles on it. If the seller will not make that guarantee, then heis admitting that the mileage is probably not accurate and byimplication may well have been turned back. If the seller willnot make that guarantee, consider a compromise, such as $100maximum cost. If not acceptable, walk away and look elsewhere." Before buying any car, especially 4-cylinder foreign cars, oreven 6-cyl. BMW, be aware of the unavoidable cost of $400-$800to replace the timing belt at anywhere from 50,000 to 70,000miles if the car has an 'interference' type of engine. The salesperson will invariably not mention that an 'interference' typeengine powers the vehicle and may not even know what one is. Ifa timing belt on an interference engine is not replaced atrecommended intervals, the repair cost when the belt breaks (notgradually, but always catastrophically) could increase to $3,000to $5,000 due to engine failure because parts have smashed intoeach other An 'interference' engine is an engine design that has beenavoided by some manufacturers for well over 80 years. GeneralMotors, Chrysler, etc., typically use a metal chain-type timingbelt on push-rod engines (often called a timing chain) totransmit torque from the engine crankshaft o the engine camshaftthat opens the valves that admit air and fuel. (Note: on somenew cars the fuel is admitted not through the valves but throughinjectors in the top of the cylinder. Rather than use a steeltiming chain, interference engines may use a rubber timing beltwith its limited life, whereas steel timing belts typically last150,000 to 200,000 miles or more. Valves open further in an interference engine and projectfurther into the combustion chamber than in a 'free-running'engine. This allows outside air at atmospheric pressure flowfaster into the combustion chamber through the larger valveopening. The engine can therefore inhale more air, be a littlesmaller, and still create as much power while reducing its.manufactured cost and also guaranteeing future repair businessfor its dealer. If a rubber timing belt breaks by not beingreplaced soon enough, some of the valves stuck in their openposition will collide with the top of the pistons, therebybreaking or irreversibly damaging one or the other or both. Tomake matters worse, it is not possible to measure the wear onsuch a rubber belt so that it could be replaced when there issome indication of imminent failure. Failure in these belts iscatastrophic, without warning. This will require a whole newengine be installed. Woe to the owner. Finally, the rubber beltmay have to be replaced long before 60,000 miles solely due toits age. This is really playing a bad poker hand. Interferenceengines are like a time bomb waiting to explode unless replacingthe timing belt at the recommended interval. Be aware of thatguaranteed future expense before buying a new car, or especiallya used car, " with such an engine. For details on this subject or for recommended mileage toreplace rubber timing belts on interference engines, connect onthe Internet to Gates.com. When its web site appears, click onReplacement parts/Automotive. Look for 'Timing belt replacementGuide'. |
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