How to check for Belt proper belt tension?

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dixon5553
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How to check for Belt proper belt tension?

Post by dixon5553 »

Without the aid of a force gauge, what is the best way to check the fan belt tension? How much deflection should there be when pushing down on it with a slight force, in inches? This would be a LM 110HP engine. Thanks
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66CorsaConv
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Re: How to check for Belt proper belt tension?

Post by 66CorsaConv »

Take a look at Brad Bodie's reply to the Belt Idler Pulley question from earlier. Brad does it like I always have. I did throw a belt this summer. Put 250 miles on it after a 2-year storage.

How is yours running after we did those carbs a couple winters back?
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bbodie52
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Re: How to check for Belt proper belt tension?

Post by bbodie52 »

Here is a copy of my earlier post...
Brad Bodie wrote:ImageImage
There are two 9/16 inch fasteners securing the idler pulley. The hole and the separate groove (or slot) in the above photograph shows the locations where bolt and nut tension is applied to secure the idler pulley in place. Late-model cars that are fitted with a magnesium blower also have belt guides at the idler pulley and at the main fan pulley. Specified clearance between the belt/pulley and each belt guide is 1/16 of an inch. The idler pulley tension must be adjusted to provide both proper belt tension and proper clearance between the belt and the belt guide.

A good rule of thumb (literally) when adjusting belt tension is that proper tension has been achieved if there is a slight slippage between the belt and the alternator/generator pulley when pressure is applied with your thumb to the alternator/generator cooling fan blade. If there is no slippage the belt is likely too tight.

Tightening a Corvair fan belt w/ordinary tools
1961 Shop Manual, Page 7-4 wrote:Adjust belt (if necessary) to give a 3/8" deflection between blower and idler pulley under a 15 pound load. If a new belt is installed, adjust deflection as described above, then operate the engine at 1500 rpm for at least one minute to "seat" the new belt. Recheck deflection.
Changing a Corvair fan belt without tools.


Image
The above procedure is a little rough on the belt, but can work if there is adequate gap between the belt guides at the idler pulley and the main fan pulley to permit the belt to be pushed in past the belt guides. Also, be sure to use a procedure that places the belt around all pulleys, with the alternator or generator pulley being last. The other pulleys have deeper belt grooves so forcing the belt over the deep edges of the pulley is more likely to cause damage to the belt.

The image above displays the support strands that are embedded around the perimeter of the belt to provide it with tensile strength. A belt that has flipped off from the Corvair pulleys on its own may have suffered damage to these support strands that are internal and hidden from view. However, one or more damaged strands within the belt can severely weaken its overall tensile strength, which means it is likely to flip off again as it stretches if a damaged belt is reused. If installing a belt without tools (as shown in the video), you should be careful not to stress the belt excessively to the point where internal damage might be incurred.
Brad Bodie
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Image 1966 Corvair Corsa Convertible
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Re: How to check for Belt proper belt tension?

Post by 66vairguy »

dixon5553 wrote:Without the aid of a force gauge, what is the best way to check the fan belt tension? How much deflection should there be when pushing down on it with a slight force, in inches? This would be a LM 110HP engine. Thanks
Forget the force guage. As Brad described, the most common method is the alternator/generator fan test. Typically it will take more force to move the fan one way vs. the other. An excessively tight belt causes premature cooling fan bearing failure and the belt tends to "flip" off much easier. Oh, expect the belt to stretch when new and require a few adjustments the first couple of hundred miles.

Other issues that cause fan belts to flip off/over: rust on the pulley, belt is too wide (FLAPS or Gates book shows wrong belt # for the Corvair), main fan bearing height wrong (range per testing show you want to be +/- 1/8" of an inch of ideal).
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66CorsaConv
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Re: How to check for Belt proper belt tension?

Post by 66CorsaConv »

Funny thing to read this now. Back in May the belt that came on mine shredded. Just old and cracking. It flew apart. Lucky I found all the chunks. None went down the fan. I've had it 8 years. I put on the spare that came with the car and picked up one at a big box store that the make and model of the belt is actually on a few of you guys' preferred lists.

The "new" old one is a little lose after 255 miles. Alternator pulley a little easy to rotate. So in the spring a little tweak.

She's up on jack stands and the top is up for winter garage storage in the Up-North house.
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