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Quite necessary Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Wed, 11 Aug 2004 08:18:09 In Reply to: What is an idler pulley?, joshua, Wed, 11 Aug 2004 00:43:30 Members do not see ads below this line. - Help Keep This Site Online - Signup |
"Idler Pulley" is the conventional name for a pulley that does not provide drive. The water pump has a pulley, and that takes energy from the belt to drive the water pump. An idler pulley just acts as a guide or turning point for the belt.
OK, why have one? Why not just run the belt between all the accessories? Two big reasons. First, you can't mount the accessories just anywhere - they need to interface to the engine (like water pump and main pump), or be otherwise located in the engine compartment so they don't hit things (alternator, AC compressor, etc.) Second, and the biggest, is that a belt just isn't a rubber band going from place to place. A belt is a power transmission system, and the angle the belt approaches and leaves a pulley (and the contact surface on the pulley) is critical to how much power it can transmit. That's different for each accessory. You also can't let the belt run a long distance without support - depending on load and engine speed, it can become unstable (flap). Most of the time you can't mount all the accessories in just the right places so that you meet the requirements of belt contact angle on the pulleys, and meet certain other max and min distance requirements.
That's the fun thing about a lot of this stuff. It's a lot more complex than it looks.
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