| Interference Engines: ........ Useful information by An | | | | When buying a used car always insist on |
| interference engine is an engine design that has | | | | determining if the vehicle has a rubber timing-belt. |
| been avoided by some manufacturers for well | | | | Be aware that about five years ago an |
| over 80 years. General Motors, Chrysler, etc., | | | | International Oil Company did a follow up on 5,000 |
| typically use a metal chain-type timing belt on | | | | cars it had turned back after 3 year leases and |
| push-rod engines (often called a timing chain) to | | | | traced them to their eventual private owners. All |
| transmit torque from the engine crankshaft o the | | | | the cars had by then passed through wholesale |
| engine camshaft that opens the valves that admit | | | | auction markets and likely one or more retail |
| air and fuel. (Note: on some new cars the fuel is | | | | dealers before being sold to a private owner. The |
| admitted not through the valves but through | | | | survey disclosed that 50% of the cars had their |
| injectors in the top of the cylinder. Rather than | | | | odometers illegally turned back. |
| use a steel timing chain, interference engines may | | | | When buying a used car, supposedly with 40,000 |
| use a rubber timing belt with its limited life, | | | | miles for example, and determining it has a rubber |
| whereas steel timing belts typically last 150,000 to | | | | timing belt, insist on a written guarantee from the |
| 200,000 miles or more. | | | | seller to guarantee in writing to replace the timing |
| Valves open further in an interference engine and | | | | belt at no charge if it fails within another 20,000 |
| project further into the combustion chamber than | | | | miles, a typical recommended total amount (call |
| in a 'free-running' engine. This allows outside air at | | | | any Dealer to get the recommended amount for |
| atmospheric pressure flow faster into the | | | | the particular make of vehicle). After all, the |
| combustion chamber through the larger valve | | | | vehicle may in fact already have 55,000 miles on |
| opening. The engine can therefore inhale more air, | | | | it. If the seller will not make that guarantee, then |
| be a little smaller, and still create as much power | | | | he is admitting that the mileage is probably not |
| while reducing its manufactured cost and also | | | | accurate and by implication may well have been |
| guaranteeing future repair business for its dealer. | | | | turned back. If the seller will not make that |
| If a rubber timing belt breaks by not being | | | | guarantee, consider a compromise, such as $100 |
| replaced soon enough, some of the valves stuck | | | | maximum cost. If not acceptable, walk away and |
| in their open position will collide with the top of the | | | | look elsewhere." |
| pistons, thereby breaking or irreversibly damaging | | | | Before buying any car, especially 4-cylinder foreign |
| one or the other or both. To make matters | | | | cars, or even 6-cyl. BMW's, be aware of the |
| worse, it is not possible to measure the wear on | | | | unavoidable cost of $400-$800 to replace the |
| such a rubber belt so that it could be replaced | | | | timing belt at anywhere from 50,000 to 70,000 |
| when there is some indication of imminent failure. | | | | miles if the car has an interference type of |
| Failure in these belts is catastrophic, without | | | | engine. The sales person will invariably not mention |
| warning. This will require a whole new engine be | | | | that an interference type engine powers the |
| installed. Woe to the owner. Finally, the rubber belt | | | | vehicle and may not even know what one is. If a |
| may have to be replaced long before 60,000 | | | | timing belt on an interference engine is not |
| miles solely due to its age. This is really playing a | | | | replaced at recommended intervals, the repair |
| bad poker hand. Interference engines are like a | | | | cost when the belt breaks (not gradually, but |
| time bomb waiting to explode unless replacing the | | | | always catastrophically) could increase to $3,000 |
| timing belt at the recommended interval. Be | | | | to $5,000 due to engine failure because parts |
| aware of that guaranteed future expense before | | | | have smashed into each other |
| buying a new car, or especially a used car, " with | | | | If the sales person does not know if the vehicle |
| such an engine. | | | | has an interference engine, walk out to the repair |
| For details on this subject or for recommended | | | | shop and ask the 'Service writer', who is probably |
| mileage to replace rubber timing belts on | | | | a former mechanic. Finally, since words are cheap, |
| interference engines, connect on the Internet to | | | | write on the purchase order that the seller |
| ©Gates Rubber Company, a worldwide | | | | guarantees the engine is not a "interference |
| manufacturer of such belts. When its web site | | | | engine" and will indemnify you 100% if it turns out |
| appears, click on Replacement parts/Automotive. | | | | that it is and the engine breaks when the rubber |
| Look for 'Timing belt replacement Guide'. | | | | timing belt breaks. |