By
Ralph Hoffmann
Interference
Engines: ……..Free Useful informatio
When buying a used car always insist on determining if the vehicle has a rubber
timing-belt. Be aware that about five years ago an International Oil Company did
a follow up on 5,000 cars it had turned back after 3 year leases and traced them
to their eventual private owners. All the cars had by then passed through
wholesale auction markets and likely one or more retail dealers before being
sold to a private owner. The survey disclosed that 50% of the cars had their
odometers illegally turned back.
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, a typical recommended total amount (Call any
Dealer to get the recommended amount for the particular make of vehicle). 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, or even 6-cyl. BMW,
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. The sales person will invariably not mention that an 'interference' type
engine powers the vehicle and may not even know what one is. 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 smashed into each
other
An 'interference' engine is an engine design that has been avoided by some
manufacturers for well over 80 years. General Motors, Chrysler, etc., typically
use a metal chain-type timing belt on push-rod engines (often called a timing
chain) to transmit torque from the engine crankshaft o the engine camshaft that
opens the valves that admit air and fuel. (Note: on some new cars the fuel is
admitted not through the valves but through 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 project 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 whole new engine be
installed. Woe to the owner. Finally, the rubber belt may have to be replaced
long before 60,000 miles solely due to its age. This is really playing a bad
poker hand. 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.
For details on this subject or for recommended mileage to replace rubber timing
belts on interference engines, connect on the Internet to http://www.gates.com/brochure.cfm?brochure=2389&location_id=3053,
a worldwide
manufacturer of such belts. When its web site appears, click on Replacement
parts/Automotive. Look for 'Timing belt replacement Guide'.
Visit http://www.AutoTruckData.com for related resources
Copyright 2204-2005 by Beacon Data LLC.
Reprinted with permission
About the author:
Ralph Hoffmann has a major in Applied Mathematics, and became fascinated with
the anomalies inherent in automotive leasing. His web site http://www.autotruckdata.comaddresses
some of the fascinating results.
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