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Warning Needed for Timing Belts

They are sometimes derisively called “rubber bands,” but they are among the most critical items in an engine; they are known among mechanics as timing belts.

On many cars, a timing belt failure will cause serious damage to the engine and sometimes even ruin it. On other cars, a timing belt failure will cause no damage at all.

It would be helpful for motorists to know whether the timing belts in their engines are the type that will cause severe damage or not. But don’t look in your owner’s manual for the information. Automobile manufacturers seldom give very much guidance on this arcane subject.

A timing belt is a notched rubber belt that transfers power from the crankshaft to the camshaft, which operates the engine valves. If the belt breaks or slips, it could allow a valve to open at the improper time.

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In some engines, a valve that opens at the incorrect instant will hit the top of the piston and damage either the piston or the valve. In some cars, notably BMWs, the broken piston has even been known to crack the cylinder block. At that point, the engine is junk.

I recently received a letter from the owner of several Toyota Camrys. He experienced a timing belt failure on a 1984 model at 102,000 miles and a failure in his 1985 model at 77,000 miles. Now he is concerned about his 1985 model.

His mechanic wants him to replace the belt after just 50,000 miles. I suppose that would be prudent, but who wants to spend $150 to $200 unless it is necessary?

Toyota engineers note that 1984 Camrys had problems because oil leaks could damage the rubber belt. Since 1986, the four-cylinder Camry engine has undergone substantial change. And a new V-6 engine was introduced.

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Despite what mechanics say, Toyota has never recommended regular or periodic changes of timing belts. The reason is that the pistons have a notch or an eyebrow that allows enough clearance for a valve even if it opens at the incorrect time, according to Toyota technical representatives.

If a belt does break, the engine will not operate, but it will not be damaged. A regular inspection of the belt, which is done by simply removing the front timing cover, can be done for as little as $25, according to Toyota technicians.

Honda is a different story altogether.

Although Honda made no specific recommendation originally, it has notified owners of 1984 and 1985 models that the timing belts should be changed at 60,000 miles. The company found that a small percentage of these cars would experience failures after 60,000 miles.

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Honda still makes no official recommendation for cars between 1986 and 1990 or before 1984. Honda service experts informally suggest a 90,000 mile change on the cars since 1985 and 60,000 miles on cars made before 1984. In 1990, Honda began advising owners of its new cars to change the belts after 90,000 miles.

Most of the time, Accord engines will not bend a valve even if a belt breaks, whereas Civic engines will bend a valve almost every time, Honda representatives say.

Still, even this cautious advice will not prevent every calamity. A Los Angeles reader wrote me that his 1985 Accord suffered a timing belt failure at 43,000 miles.

I wish I could give a rundown on the timing belt statistics for every make and model car, but I don’t have the space. If you are curious, you ought to write the manufacturer and ask for its specific recommendation. I’ll be the first to say: This information ought to be in the owners manual in the first place.

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Vartabedian cannot answer mail personally but will attempt to respond in this column to automotive questions of general interest. Do not telephone. Write to Your Wheels, Times Mirror Square, Los Angeles, CA. 90053.


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