Sunday, May 29, 2011

Serpentine Belt Replacement

[I'll be dealing with the serpentine belt on a 1999 Ford Ranger, 3.0 litre V6 w/o A/C here, but most of what follows is applicable to any vehicle's belt.]

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Serpentine belts are a brilliant piece of engineering -- I consider them a huge advance over the old V-belts. But they do present a couple of small challenges if you're new to the job of replacing one.

The first thing you need to get is a wrench that will enable you to crank the tension idler pulley away from the installed belt. Tension idler pulleys are strongly sprung, and an ordinary combination wrench is unlikely to be long enough. If the hex in the centre of the pulley has sufficient clearance in front of it, a breaker bar with a shallow socket will work fine. Odds are, though, that the pulley will be in cramped quarters, and you'll need something with a much lower profile to get on the pulley's hex.

Purpose-made wrenches can be had from an auto supply. I solved the problem for my Ranger by modifying an inexpensive 15mm combination wrench as in the following photograph.

I heated the wrench near its open end to about dull red and gave it a 90° twist. Now I can clamp a set of vise-grips on it for extra leverage while the box end is on the tension idler's hex. It works quite nicely. (An ordinary propane torch burning the hot fuel is entirely adequate for heating a wrench for this purpose.)

Once you have a suitable wrench, you're ready to go, but a word of caution is in order first.

If you're a gifted natural mechanic who can just intuit how things go together, go right ahead and remove and replace your belt. If your abilities are a bit shy of the 'gifted' characterization, as are mine, don't even think about removing the old belt until you have an accurate sketch of its path on hand. You'd be surprised at how mind-boggling a serpentine belt can be when you're confronted by a barren array of pulleys, a new belt in hand and nothing to guide you.

The packaging sleeve of a new belt will likely have what you need already printed on it, like so.

Those are excellent drawings, but play it safe and take a moment to confirm that a drawing agrees with what you see on your vehicle. If you don't have a belt-path drawing for your vehicle, make one. It needn't be draughtsman-quality, just clear and unambiguous.

With your wrench in place and the tension idler cranked you can slip the old belt off the idler, then off the alternator pulley and remove it from the pulley array entirely. The job is complicated a bit on the Ranger by the presence of a huge cooling fan that the belt must be coaxed over frontward for complete removal.

In any event, you'll arrive at a point where you're at an obvious end/beginning, like this.

On the Ranger, it's the power steering pump's pulley. Any pulley array will have an analogous place in it. That's where you start from with the new belt. With that starting point in mind and your sketch at hand, you can't go wrong.

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