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Timing belts: time to belt up

July 18, 2012
Fort Myers Beach Bulletin, Fort Myers Beach Observer

It might be time to belt up. What the heck does that mean? What is a timing belt, and why do I have to have it changed? Can't car manufacturers make one that lasts longer? It runs the camshaft; it might ruin the engine if it breaks. And, no, are your three answers.

This gets a little technical, but I'll keep it light because lots of people have heard about them, but not many understand the problems. Every engine has a camshaft. Actually some have one, some have two and some have four camshafts. These shafts rotate and operate the valves. These shafts are hard to rotate because the valves are hard to open against strong spring pressure. To rotate the camshafts they are connected to the engine crankshaft, which is where the engine's power is located. So the crankshaft pulls the camshaft by either a chain, which is like a bicycle chain, or by a rubber belt that has teeth in it to avoid slipping. Either system wears out because of the heavy load it is under.

Back before the 1980's, most engines used chains. They were a common failure, usually at around 100,000 miles. Some engines still use chains, but many have converted to rubber belts. My guess is the change was because belts are cheaper to make, lighter weight, and quieter to operate, but it's only a guess. Detroit didn't check with me before they converted, so I'm not to blame. Manufacturers usually recommend changing the belts at either 60,000 miles or sometimes 90,000 miles. Chains, for some reason, seem to be lasting much longer these days.

Here's the rub. Some engines will be heavily damaged if the belt slips or breaks, and others will not be damaged. However, both types will stop running instantly when it happens. The ones that are damaged are called "interference" engines, meaning the valves will be hit by the pistons if the valves stop, bending the valves and possibly punching holes in the pistons. The other type of engine is called "free-wheeling", which means the valves are not hit by the pistons. It cannot be generalized as to which cars have which kinds of engines; most manufacturers make both kinds of engines. Your mechanic can look it up for you if you're curious, but going past the recommended interval is foolish with either type of engine.

The replacement of the timing belt is not easy on any engine and downright hard to do on some engines. It is definitely not something to try at home because the exact timing between the various shafts is critical, and a mistake on an interference engine could cause the same damage as a broken belt. The procedure usually involves removing all of the other belts and some pulleys, and possibly even the water pump on some engines. If there are oil leaks from the various shaft seals, it would be a good time to replace those seals because most of the labor is already done.

If you feel angry about the prospect of having the work done, just remember, your mechanic didn't design it, didn't build it, didn't sell it to you and didn't wear it out. They're here to help. Be nice.



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