Tensioning Drive Belts

[The Critic]

My father has a 92 Toyota Previa with 86,000 miles. It still has the original belts on it.

At the upcoming 90,000 mile service, I plan to replace the Alternator/PS and Air Conditioning belts with new belts from the dealer. Although the belts still look fine, I figured that it is a good idea to replace them as preventive maintenance considering their age.

Unfortunately, I do not own a belt tensioning gauge, so I am not sure how to correctly tension the belts. The service manual gives me the following information:

1.
New belt= 160-180 ft. lbs
Used belt= 115-135 ft. lbs

2.

Belts are normally adjusted by loosening the bolts of the accessory being driven and moving that accessory on its pivot points until the proper tension is applied to the belt. The accessory is held in this position while the bolts are tightened. To determine proper belt tension, you can purchase a belt tension gauge or simply use the deflection method. To determine deflection, press inward on the belt at the mid-point of its longest straight run. The belt should deflect (move inward) 3 / 8 - 1 / 2 in. (10-13mm). Some long V-belts and most serpentine belts have idler pulleys which are used for adjusting purposes. Just loosen the idler pulley and move it to take up or release tension on the belt.

How should I set the belt tension? Do I need to go buy a belt tension gauge ($$$) or can I use the deflection method?

Thanks!

 

[oilboy123]

Regular V belts should be over tightened because they stretch after break in. Or you can go back and tighten them again.

IMO it is best to over tighten them and check later to see if they are OK after some run in time. I have never messed with a tension gauge. I would use the deflection method.

 

[doitmyself]

Excellent question Critic! I've been doing it by feel/deflection for 35+ years, but I always worry about over tightening and damaging shaft bearings.

Most "authorities" claim the deflection method is risky, yet I imagine 99% of mechanics do it this way. How do you teach someone the "feel" method? How hard does one push to get 1/2" deflection?

Waiting for answers....

In the mean time, a google search shows good reviews of the Gates Krikit V-Belt Tension Gauge as shown here:

http://www.amazon.com/Gates-91107-Belt-T...49335813&sr=8-1

Rock Auto is selling it for $10.88, and the other model for ribbed v belts for $14.78!!

Anyone have experience with these? One would think Gates would have a good product.

 

[djb]

Originally Posted By: oilboy123
Regular V belts should be over tightened because they stretch after break in. Or you can go back and tighten them again.

IMO it is best to over tighten them and check later to see if they are OK after some run in time. I have never messed with a tension gauge. I would use the deflection method.


This is very bad advice, based on obsolete information.

The fabric (usually polyester) that provides the strength of modern belts is made with pre-stretched fibers to minimize later elongation. With age and heating the fabric is more likely to shrink than stretch. Not what you might expect, although it's not that different than clothing shrinking.

If you are going to guess the tension, err on the side of being too loose. It's easier to re-tension the belt later than replace the front bearing on alternators, A/C compressors etc.

 

[doitmyself]

Originally Posted By: djb
Originally Posted By: oilboy123
Regular V belts should be over tightened because they stretch after break in. Or you can go back and tighten them again.

IMO it is best to over tighten them and check later to see if they are OK after some run in time. I have never messed with a tension gauge. I would use the deflection method.


This is very bad advice, based on obsolete information.

The fabric (usually polyester) that provides the strength of modern belts is made with pre-stretched fibers to minimize later elongation. With age and heating the fabric is more likely to shrink than stretch. Not what you might expect, although it's not that different than clothing shrinking.

If you are going to guess the tension, err on the side of being too loose. It's easier to re-tension the belt later than replace the front bearing on alternators, A/C compressors etc.




djb, do you have any links or references to your information? I tension v belts at my work place on misc. equipment and all of the belt manufacturers list a new/initial belt tension setting (higher) and a used/re-tension belt tension (lower). These recommendations are from current catalogs.

I.E, here is a Browning pamphlet that shows this:

http://www.mpair.com/library.active/general.information/belt.tensioner.pdf This is example is dated 1999, but the new catalogs show the same info.

Maybe oilboys use of the term "over tighten" is not quite correct. But it seems to me that new belts should be "more" tight initially, then checked after run in for proper tightness.

 

[oilboy123]

Originally Posted By: djb
Originally Posted By: oilboy123
Regular V belts should be over tightened because they stretch after break in. Or you can go back and tighten them again.

IMO it is best to over tighten them and check later to see if they are OK after some run in time. I have never messed with a tension gauge. I would use the deflection method.


This is very bad advice, based on obsolete information.

The fabric (usually polyester) that provides the strength of modern belts is made with pre-stretched fibers to minimize later elongation. With age and heating the fabric is more likely to shrink than stretch. Not what you might expect, although it's not that different than clothing shrinking.

If you are going to guess the tension, err on the side of being too loose. It's easier to re-tension the belt later than replace the front bearing on alternators, A/C compressors etc.



All this theoretical stuff is fine and dandy, but it means squat in the real world. Yes maybe over tighten is not a good term.......
"A little tighter tension" might be a better way to put it. I can't tell you how many times I I had belts that were put on at the perfect tension only to end up being too loose and flopping around or squealing later on......


Normally in a shop environment you don't have customers come back to do the belts twice. So it's not practical, unless you are working at home and like to do the job twice. The tension gauge would be the way to go I guess.......I never tried one.

 

[Junior]

Originally Posted By: djb
Originally Posted By: oilboy123
Regular V belts should be over tightened because they stretch after break in. Or you can go back and tighten them again.

IMO it is best to over tighten them and check later to see if they are OK after some run in time. I have never messed with a tension gauge. I would use the deflection method.


This is very bad advice, based on obsolete information.

The fabric (usually polyester) that provides the strength of modern belts is made with pre-stretched fibers to minimize later elongation. With age and heating the fabric is more likely to shrink than stretch. Not what you might expect, although it's not that different than clothing shrinking.

If you are going to guess the tension, err on the side of being too loose. It's easier to re-tension the belt later than replace the front bearing on alternators, A/C compressors etc.



What??? Every v-belt I have ever used has an initial run in period where it will stretch and conform to the pulleys. This equates to about 0.5 to 1% belt stretch and the need to readjust tension within the first 50-100 hours of use. I suppose our belt suppliers could be wrong though.....

Ah yes, I wonder how to teach the feel method. I have heard of the quarter turn method. Tension the belt until you can only twist it 1/4 or a little less. Never tried it though.

 

[chrome]

Does the Previa have serpentine belts or regular V belts?

In the days before automatic tensioners, with both types of belt, I go for the rule of thumb of about 1/2" deflection in one direction of the longest distance between two pulleys. I just push the belt with moderate force, not excessively because it starts to hurt my finger.

Then I start the engine up, let it idle for a few minutes, and give it a good rev while looking at the belt at the location where I measured the deflection. The sudden change in rpm from high to low (changing loads on the belt) will cause the belt to deflect, just observe that deflection to make sure it is not excessive. I tend to aim for less deflection on a serpentine belt.

 

[andyd]

I change belts with the timing belt at 60k miles. I tend to run the belts a tad loose, 3/4" deflection instead of 1/2". If I remember, I will check tension in a month. So far so good, I dont eat up accessory bearings very often. I would much rather waste a 10$ belt than an alternator or a waterpump etc.

 

[mechtech2]

The internal construction of modern belts may not actually stretch. but the rubber outside seats in and wears, for sure.
Go a bit tight with a new belt - don't go crazy with it. Recheck it after a few weeks.

 

[tom slick]

Mr. Critic,
Sounds like a good excuse stroke your snap-on fetish. you "need" a belt tension gauge!

 

[JakeR22]

Originally Posted By: mechtech2
The internal construction of modern belts may not actually stretch. but the rubber outside seats in and wears, for sure.
Go a bit tight with a new belt - don't go crazy with it. Recheck it after a few weeks.


I agree. No need to overthink this stuff.

 

[berniedd]

Call me old school, but I'd prefer to set a new belt with the correct tension, then go back and readjust it after a few weeks.

 

[oilboy123]

Originally Posted By: berniedd
Call me old school, but I'd prefer to set a new belt with the correct tension, then go back and readjust it after a few weeks.


You are old school...........

 

[mechtech2]

BTW, IMO, those gauges are worthless.

 

[pbm]

Originally Posted By: berniedd
Call me old school, but I'd prefer to set a new belt with the correct tension, then go back and readjust it after a few weeks.


You may be 'old school' but I think you have it correct.

 

[mechtech2]

Counting on the inevitable re-tensioning is NOT something a paid mechanic wants to do.
So professionally, I give the adjustable belts a bit more tension than normal, when new.

 

[oilboy123]

Originally Posted By: mechtech2
Counting on the inevitable re-tensioning is NOT something a paid mechanic wants to do.
So professionally, I give the adjustable belts a bit more tension than normal, when new.


That is just what I said in the first place........thanks for backing me up.

 

[JakeR22]

If the belt slips, or falls off, it's to loose. ;-)

 

[Drew99GT]

I don't buy into the whole deflection deal, as deflection is directly related to the distance between pullies, so just going by 1/4 inch or whatever could mean too tight if pullies a closer together, or too loose if they are far apart. Just wiggle the belt! If there's a lot of slop in it and it doesn't feel "snug", cinch it up until it's "snug". Don't go gangbusters and crank the [censored] out of it. My old boss I worked for at a courier service had the belts so tight, all the accessory bearings screamed like a scolded cat when the engine was cold. I checked the belts one day and you could hardly even move them!