How do you properly tension a belt for an alternator?

Site Notices

[ARCHIVED THREAD] - How do you properly tension a belt for an alternator?

Posted: 8/18/2004 9:09:32 PM EDT

I know how to change out the alternator on my car. I'll be doing that tomorrow afternoon. My question is how do you tell if you've tensioned the belt enough, or too much?

I need to tension my belt to a maximum of 145 lbs, but the manual doesn't say a minimum tension...

I'm probably going to have to "wing it" by hand and guessing if they're about the same tension. If things don't work out, there's trial & error.

Posted: 8/18/2004 9:10:21 PM EDT

[#1]

You know...if you told us what type of car it JUST MIGHT HELP!!!!!!!!

Sgtar15

Posted: 8/18/2004 9:11:31 PM EDT

[#2]

Quoted:
You know...if you told us what type of car it JUST MIGHT HELP!!!!!!!!

Sgtar15

Very good point. They are not all the same.

Posted: 8/18/2004 9:11:50 PM EDT

[#3]

If it's the old type without a tensioner pulley, just pry it over like a mofo and tighten it with the other hand (pry with the biggest screwdriver you have or other pry bar), and it will be tight enough for about a week, until the new belt wears in. Repeat if necessary (likely). I'm not a mechanic, and I did not sleep at a whatever last night. YMMV

Posted: 8/18/2004 9:12:45 PM EDT

[#4]

Quoted:
You know...if you told us what type of car it JUST MIGHT HELP!!!!!!!!

Sgtar15

Sorry, it's a 1985 Oldsmobile Cutlass Supreme Brougham. Fantastic condition, great uncle's old car (now mine) with only 86,000 miles on it.

Like I said, I know how to tighten the belt and bolt its brackets & stuff in place. How do you test the tension of the belt to make sure it's not TOO tight or TOO loose?

Posted: 8/18/2004 9:14:29 PM EDT

[#5]

Quoted:
If it's the old type without a tensioner pulley, just pry it over like a mofo and tighten it with the other hand (pry with the biggest screwdriver you have or other pry bar), and it will be tight enough for about a week, until the new belt wears in. Repeat if necessary (likely). I'm not a mechanic, and I did not sleep at a whatever last night. YMMV

Yes, it doesn't have the pully and I'll have to pry the crap out of it until it's tight enough. But how tight?

Will I need to buy a new belt for this as well, or will the current one (that doesn't show hardly any wear) suffice (at least for now)?

Posted: 8/18/2004 9:14:31 PM EDT

[#6]

I am assuming it does NOT have a tensioner pulley on that motor.

Basically tighten it as tight as you can. It then should have about 1/2" of play in the belt at the longest section.

SGtar15

Posted: 8/18/2004 9:15:22 PM EDT

[#7]

Quoted:
I know how to change out the alternator on my car. I'll be doing that tomorrow afternoon. My question is how do you tell if you've tensioned the belt enough, or too much?

I need to tension my belt to a maximum of 145 lbs, but the manual doesn't say a minimum tension...

I'm probably going to have to "wing it" by hand and guessing if they're about the same tension. If things don't work out, there's trial & error.

Loosen alternator...

Pull REALLY REALLY HARD to apply tension...

Tighten bolt...

Posted: 8/18/2004 9:15:27 PM EDT

[#8]

I HIGHLY doubt you can over tighten this belt....unless you REALLY SERIOUSLY pull on it.

SGtar15

Posted: 8/18/2004 9:16:20 PM EDT

[#9]

If it is too loose you will know by a loud screaming noise at start up. Don't pry like a maniac either or you could put undo wear on your bearings in your water pump and alternator.

Posted: 8/18/2004 9:16:49 PM EDT

[#10]

Don't over tighten or you can wear out your bearing in the alt.

Like sarge said, make sure you have a little play.

Posted: 8/18/2004 9:17:02 PM EDT

[#11]

Good advice, guys!

Shit you people are FAST with responses!!!

Thanks!!!

Posted: 8/18/2004 9:17:39 PM EDT

[#12]

Quoted:
I HIGHLY doubt you can over tighten this belt....unless you REALLY SERIOUSLY pull on it.

SGtar15

Get a big enough bar and you can. Trust me.

Posted: 8/18/2004 9:17:41 PM EDT

[#13]

Quoted:
Good advice, guys!

Shit you people are FAST with responses!!!

Thanks!!!

We live to help people.

It is our calling.

SGtar15

Posted: 8/18/2004 9:17:48 PM EDT

[#14]

Quoted:
Quoted:
If it's the old type without a tensioner pulley, just pry it over like a mofo and tighten it with the other hand (pry with the biggest screwdriver you have or other pry bar), and it will be tight enough for about a week, until the new belt wears in. Repeat if necessary (likely). I'm not a mechanic, and I did not sleep at a whatever last night. YMMV

Yes, it doesn't have the pully and I'll have to pry the crap out of it until it's tight enough. But how tight?

Will I need to buy a new belt for this as well, or will the current one (that doesn't show hardly any wear) suffice (at least for now)?

As tight as you can get it is "tight enough." As sgtar15 said--about 1/2" of play in the longest distance area between two pulleys--which ain't much. Too tight would, in theory, wear the bearings, but you ain't gonna get it too tight. I always replace belts while I'm messing with it. It's a real PITA to do it along the road--at 2:00 AM (IF you can obtain one at that hour). Save the old belt(s) in case one ever breaks.

Posted: 8/18/2004 9:18:31 PM EDT

[#15]

You know you've tightened it enough when

1. The alternator generates electricity and charges the battery

2. The belt doesn't squeal like Ned Beatty.

Posted: 8/18/2004 9:20:36 PM EDT

[#16]

Quoted:
Quoted:
I HIGHLY doubt you can over tighten this belt....unless you REALLY SERIOUSLY pull on it.

SGtar15

Get a big enough bar and you can. Trust me.

If he has to ask for such basic info he does not have a big enough pry bar to over-tighten. Those 3' mofos with the tapered slight "hook" at the end WILL over-tighten, but he doesn't have one. (I'd bet.)

Posted: 8/18/2004 9:22:22 PM EDT

[#17]

Over-tightening your fan belts (especially on older cars, with multiple belts that go around the water pump) can shorten water pump life. Too much tension one way can cause the water pump's shaft to pull to one side, prematurely wearing it. BEST advice? Go buy a belt tension gauge. Probably unecessary, but if you want to tension to the specified 145lbs, do it.

Posted: 8/18/2004 9:23:59 PM EDT

[#18]

Jeez, even MORE great advice... I guess I'll be picking up two belts tomorrow when I pick up my new RMFD (remanufactured?) 79 AMP Alternator tomorrow morning.

Monday I needed a jumpstart to get to work... Batter always gets VERY low when I use too many things in my car all at once...
-Rear defroster
-Power windows (Power Anything)
-Stereo
-Blinkers
-Air Conditioner

If I'm using any 2 or 3 at once my battery drains, and it sometimes doesn't start up then...

An electrical diagnostic check stated that my current Alternator was only generating about 42 to 45 AMPs and which is barely enough to keep it running, but not keep it running with so many electrical creature comforts operating...

Posted: 8/18/2004 9:24:20 PM EDT

[#19]

did you use a factory belt or a cheapo?

I used some cheapos on a car I have and it was screaming like a stuck pig. I changed to factory belts and it went away.

Posted: 8/18/2004 9:26:31 PM EDT

[#20]

Gotta go to bed now... Need to run to work @ 6:30 AM. I'll check in tomorrow morning for more advice before I leave though...

THANKS GUYS!!!

Posted: 8/19/2004 7:14:27 AM EDT

[#21]

+1 to 1/4 to 1/2 inch of play when it is tight. There is a tool to test tension but I've never heard of any shade tree guys using one.

GunLvr

Posted: 8/19/2004 7:27:19 AM EDT

[#22]

Well, if you had a '65 Tempest, I would say that either your voltage regulator is shot or one of your windings is shot. However, all that stuff is internal now. If you have a battery gauge or a meter, when your car is at idle with minimum electrical load, your battery should be reading about 14 volts. If your belt has less then 1/2 an inch of deflection and you're pulling 14 volts, you've got it tight enough.

My Tempest has been through two alternators and two belts in four years. I have become extremely adept at swapping out alternators. I finally bought a '92 Delco 90 Amp Alt that was internally regulated and jumpered around the external regulator. No more alternator problems.

Posted: 8/19/2004 2:15:27 PM EDT

[#23]

SWEEEEEEEEEEEEEEEET!!!!!!!!

I just got back from the shop where I work. The auto-parts store ordered the wrong alternator yesterday. The RIGHT alternator I needed was an additional $40 more than the one I bought. Total came to ~$120.00! Since they found the right one at a different store in the area they had a courier deliver it right to my shop at work. It went in with no problems at all! Then I test drove it around my cemetery. Running the headlights on high-beams, the hazard lights blinking, the windshield wipers on, the AC on Max/High, stereo blaring, and the rear defroster on... SHE KEPT GOING WITHOUT A PROBLEM! The battery gauge did drop down to the yellow area, but it kept running perfectly... It was replaced with a 70 AMP alternator that actually WORKS right.

Everything is now running great.

They threw in a new alternator belt, and a large bottle of Rain-X for the inconvenience!

SWEET! My car is back up to 100% reliable again, and I didn't have to buy a spare belt (they gave me one)!

Thanks for the advice guys, it was all a great help with tensioning properly!