Timing Belts

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Timing Belts and Water Pumps

One of the challenges in designing an engine is to find a way to keep all the moving parts rotating at the right time and at the same speed.  As engines get physically smaller it is even more critical that the fast moving parts inside don’t try to be at the same place at the same time!

In the early days of engine design the crankshaft and the camshaft were mated together with gears that kept them in time with one another.  This design was absolutely reliable but not particularly efficient.  When the Europeans started mass producing small, light, powerful engines in the 1950’s with “overhead cams” the gear drive simply would not work anymore.  The European manufacturers like Alfa Romeo, Volkswagen and Audi used a chain similar to a bicycle chain to link the crankshaft and camshaft called, appropriately enough, a “timing chain”.  The timing chain was also a very reliable design, and worked well with both overhead cam and “pushrod” engines.  In the quest for ever more efficiency, manufacturers tried a toothed belt design in place of the chain.  The belt is lighter and takes less energy to move, therefore maximizing power and fuel efficiency.  There is, of course, a drawback.  While a chain could be expected to last several hundred thousand miles, the timing belt has a life expectancy of anywhere from 60,000 to 100,000 miles, depending on the engine.  While we have seen timing belts last two or even three times as long as the factory service recommendation, we have also seen them break within a few miles of the recommended replacement mileage.  We recommend following the manufacturer’s recommendation faithfully when it comes to timing belt replacement.

Many engine designs use the timing belt not only to drive the camshaft from the crankshaft, they also drive the water pump off the same belt.  This requires the use of tensioners to keep the belt taut without being too tight.  These tensioners are also a wear item. We inspect them carefully when we have them exposed as we replace the timing belt and replace as necessary.  We also like to change the water pump at this time, as a seized water pump bearing can destroy even a new timing belt in a matter of seconds.   In the 1970’s and 1980’s, water pumps had a life expectancy of 50,000 miles or so, but they were inexpensive to replace, often taking just a half hour to an hour to remove and replace.  Today’s water pumps often last to 100,000 miles but can take up to six hours to replace.  When they are driven by the timing belt we do not charge extra labor to change the water pump, considering it part of the timing belt job.

Replacing your timing belt on schedule is good insurance.  The cost of a broken belt can easily equal the cost of a new engine in most cars, not to mention the inconvenience of an unplanned breakdown.