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Old 08-22-2019, 10:23 AM   #1
50fordcoupeman
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Default Rule of thumb for fan belt tightness

Is there a rule of thumb that you guys use for belt tightness? This is for my avatar 302 engine. Thanks!!
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Old 08-22-2019, 12:38 PM   #2
Ford56
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Default Re: Rule of thumb for fan belt tightness

I've used one inch. Seems to work for me.
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Old 08-22-2019, 12:38 PM   #3
50fordcoupeman
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Default Re: Rule of thumb for fan belt tightness

Thank you 56!
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Old 08-22-2019, 02:05 PM   #4
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Default Re: Rule of thumb for fan belt tightness

I go with trying to spin the alternator pulley by hand. If I can't, it is tight enough. The # of deflection depends on how long that section of belt might be.
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Old 08-22-2019, 02:34 PM   #5
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Default Re: Rule of thumb for fan belt tightness

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I go with trying to spin the alternator pulley by hand. If I can't, it is tight enough. The # of deflection depends on how long that section of belt might be.
Thank you!!
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Old 08-24-2019, 01:56 PM   #6
Ole Don
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Default Re: Rule of thumb for fan belt tightness

Mine seemed about right, but with the headlights on during a rain the alternator would squeak. Any tighter and it was hard on bearings.
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Old 08-24-2019, 08:08 PM   #7
50fordcoupeman
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Default Re: Rule of thumb for fan belt tightness

What started this thread is that the bolt that goes thru the alt housing sheared off flush with the head. Sometimes the belt would squeal before this happened. It is a 7/16" by 6" bolt. This allowed the belt to slip significantly so both the alt and water pump stopped working. I lucked out by being able to unscrew the bolt out of the head with my fingers so I think that this bolt was loose. I put in a new grade 5 bolt. I tightened the tension so there is no squeal but the belt is quite tight-maybe a half inch on the longest travel. Is this too tight? Comments please.................
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Old 08-24-2019, 08:22 PM   #8
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Default Re: Rule of thumb for fan belt tightness

A lot depends on the accessory being turned. On my 272 the AC compressor is turned by the water pump belt. It is not the best situation in my opinion because it has to be pretty tight to run the compressor and I'm concerned about the water pump bearings.

As long as the driven accessory doesn't squeal I would think it is tight enough. The belt can get slick and hardened on the "V" and cause squealing. Check for that.

I had a 5.0 with serpentine belt that was tensioned by a factory tensioner. That joker was tight! I suppose the components were built for it.
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Old 08-24-2019, 09:35 PM   #9
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Default Re: Rule of thumb for fan belt tightness

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A lot depends on the accessory being turned. On my 272 the AC compressor is turned by the water pump belt. It is not the best situation in my opinion because it has to be pretty tight to run the compressor and I'm concerned about the water pump bearings.

As long as the driven accessory doesn't squeal I would think it is tight enough. The belt can get slick and hardened on the "V" and cause squealing. Check for that.

I had a 5.0 with serpentine belt that was tensioned by a factory tensioner. That joker was tight! I suppose the components were built for it.
Thanks 40. The belt only drives the water pump and alternator and is a fairly new belt-maybe 400 miles but I will check it anyway. I am thinking it is squealing on the alt pulley since it is the smallest. Maybe it is time for a new belt. Any advice I will try...............
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Old 08-25-2019, 06:43 AM   #10
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Default Re: Rule of thumb for fan belt tightness

Not a fix, but a band-aid is to take a bar of soap and carefully touch it to the contact side of the belt while the engine is running. Works to stop the squeal if your on the road. If the belt is still pliable with no cracks it almost has to be a matter of finding the "sweet spot" in the adjustment. I have has a new belt that just wanted to squeal and when replaced with a old used spare I had, the squeal ceased...
I wonder why belt pulleys are smooth and not knurled to better grip a belt?
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Old 08-25-2019, 10:39 AM   #11
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Default Re: Rule of thumb for fan belt tightness

an alternator needs to be tight or it will slip.they are short so the bearings will take a lot more than a generator.you can overdo it and damage the front main bearing but that would take a lot.
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Old 08-25-2019, 11:08 AM   #12
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Default Re: Rule of thumb for fan belt tightness

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Originally Posted by chap52 View Post
...
I wonder why belt pulleys are smooth and not knurled to better grip a belt?
Chap
The belt would wear really fast. Probably not even last a few weeks.
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Old 08-25-2019, 11:08 AM   #13
50fordcoupeman
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Default Re: Rule of thumb for fan belt tightness

Thanks darrell and chap. I will work on finding the sweet spot some more. Thanks all for the help!!!!
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Old 08-25-2019, 11:26 AM   #14
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Post Re: Rule of thumb for fan belt tightness

Universal Belt Tension Gauge - OTC 6673


Don't forget proper belt application/sizing, quality of belt and possible glazed pulleys.
Attached Images
File Type: jpg Universal Belt Tension Gauge - OTC 6673.jpg (4.6 KB, 52 views)
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Old 08-25-2019, 02:02 PM   #15
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Default Re: Rule of thumb for fan belt tightness

Thanks for the belt tension gauge pic, Kultulz. I've been meaning to get one of those, but didn't know what they looked like.


I've used 3/4" total lateral play slack as a standard on my '54. When my car encountered minor charging issues recently, the belt had loosened to 1-1/4" total lateral play. I didn't think that would be enough to make a difference, but when I tightened back up to 3/4" it made a measurable difference in charging. That wasn't the only issue I was facing, but it did help.
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