Timing Belt: Rubber vs. Chain

Dear Car Talk:

I bought a 2009 Hyundai Accent new back in the day. Today it has 77,000 miles on it. I always keep up with my maintenance schedule, and I even have a spreadsheet with dates and mileage when I perform maintenance.

Well, I knew it was time to change the timing belt, but that’s not cheap, so I put it off thinking I could wait. I was driving it the other day and the motor just quit on me. Guess what? The motor is destroyed because the timing belt broke and ruined the head and other parts.

I’ve learned a lesson. I won’t buy another car with a timing belt. But why would a car manufacture make such an important part out of rubber? I can’t be the only one who this has happened to. I’m looking forward to your response. — David

You’re hardly the only one. And my IRA is grateful for that, David. But your question is a fair one. Why use a rubber part when its failure can be so catastrophic? Manufacturers have asked themselves that question, too. And in many cases, they’ve switched back from rubber timing belts to metal timing chains. In fact, if you buy a new Hyundai Accent to replace the one that you just lunched, it’ll have a metal timing chain in it.

The reason car makers switched from chains to rubber timings decades ago is because they’re cheap, lightweight and simple. Obviously, a rubber belt weighs a lot less and costs a helluva lot less than a metal chain. It’s also a lot simpler.

When you add a chain, you have to encase it, lubricate it, add a tensioner, an idler pulley and guides. So you’re basically replacing a simple rubber belt with an entire chain “system.”

That added complexity also applies to repairs, and repair costs, if you ever need them. And, in fact, that was one of the reasons that rubber belts became popular for several decades — because older chain systems broke down a lot and they were expensive to fix. But modern chain systems are pretty good, as is modern engine lubrication. So most manufacturers have decided that the extra cost, weight and complexity is worth it for the extra durability and disaster prevention. And I’m guessing you would agree, David.

And modern timing chains generally last the life of the engine. Although I guess that’s not a very reassuring statement, David, since your timing belt also lasted the life of your engine. When the belt went, the engine went with it.

So let’s put it this way: In most cases, a broken timing chain won’t be what sends your next car to the boneyard.

Todays Car-o-Scope

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