Belt tension matter when replacing?

Replacing the 3 belts. I once read that if a component has been used to one tension for a long time, it could throw it off if the belt tension is not the same. Is it not that critical if the belt tension can only be pulled no more than 1/2” ? Does anyone use a belt tension reader in order to get the exact existing belt tension before swapping it out? Does it matter?

 

How does one figure out the tension if you use used parts with no idea what it was ??

I have never heard of this or saw anyone put it into practice.

 

I just replaced my belts too. I don't have a good way of checking the tension, so I made sure I could deflect them between 1/4 and 1/2 inch between pulleys (used the longer spans when possible). If they're too tight, you place too much lateral load on the driven accessory, causing bearings to fail early. This can be expensive if you wreck the PS pump bearing. Of course, if they're too loose, then the belts will slip. In a nutshell, yes, the tension matters.

@Timmah! has a video on belt replacement that demonstrates how to use a belt tension gauge, which is a fairly expensive ($150) specialty tool.

 

take the belt in the middle of the longest freespan and twist it. You are looking for 90 degrees of twist. Japanese vehicles in general like their belts tighter than most other cars. If you want the least amount of side load on the bearings, keep the tools in the truck with you, set the tightness a little on the loose side, and snug the adjustment up if you encounter belt squeal. If you want 1-and-done, 90 degrees twist.

Also, what you read once is complete horseshit. The accessories don't care about anything other than the belt tight enough to run without slipping.

 

I mean, yes, the tension matters, but it doesn't really have anything to do with what the component is "used to." If you've over tensioned the belts for a long time, that can cause the bearings to wear out prematurely, but installing new belts at that same tension will just continue to exacerbate the problem. Under tension and the belts just squeak, regardless of what the pulley is "used to."


I've never used a belt tension tool. If the belts squeak on startup, tighten them a little. 1/2" deflection is usually a good place to start

 

A belt can have been running a component for 50,000 miles with an acceptable flex of 1/4”. A new belt is put on with the acceptable flex of 1/2”. 10,000 miles later the difference in tension causes the component to go bad. Jbrant understood what I was getting at. If you’ve never heard of such an occurrence, you have now.

 

Sorry, that's not how it works. I do this stuff for a living and have changed moar belts than a weekend warrior will his entire life.

Step 1 Loosen tensioner.
Step 2 remove belt.
Step 3 spin all pulleys and check bearings.
Step 4 install new belt.
Step 5 correctly tension new belt.

The new belt, and the correlating position of the tensioner, has no relationship to the old belt or anything else. But feel free to stick to your guns, and trust 'a story I heard once' over actual correct procedures from a professional mechanic.

 

Bearings have been known to go bad with a change of belts with different tensions. I’ll stick by that but will surely set a tension “stretch” of between 1/4” and 1/2”. Perhaps the scenario I described happened where it was set different than that to begin with or after, but in the entire history of auto engines it is known to have occurred. Probably part of the reason they sell belt tension gauges. Maybe that’s for race cars or something. Anyways...thought I’d ask... 7 posts ago.

 

My read of @jbrandt 's comment suggests that he didn't agree with notion that a looser replacement belt would accelerate component wear. Hopefully he'll chime in and clarify his position.

 

I'm trying to make a good faith effort to understand your reasoning, but am having a hard time. Anyway, here are the scenarios I can think of that make sense:

1. The replacement belt is tighter than the old one, putting new excess lateral load on the bearing, leading to rapid failure.
2. The replacement belt is looser than the old one. The component failed shortly after the belt change because failure was imminent, and the looser tension on the new belt was purely coincidental. In fact, this scenario may be likely if someone is more likely to replace belts when components start making noise indicative of an imminently failing bearing.

When you say things like: "Bearings have been known to go bad with a change of belts with different tensions" or "in the entire history of auto engines it is known to have occurred", there are several issues that I see:

1. This doesn't really qualify as evidence; it's unsupported conjecture.
2. You've backed off considerably from your original assertion that components "get used to" a given tension, then fail when that tension changes, thus setting the bar much lower.
   
3. Even if true, you're describing something that can more easily be explained by other reasons: sometimes components fail due to manufacturing defects, contamination, wear from heavy use, etc. These are all more plausible than a merely "different" belt tension causing failure, unless the belt is too tight (which we already covered).

 

I’d say the most likely answer is that belts are replaced to fix a noise that’s actually a failing component.
Sorta like the “trans flush causes failures” myth.

 

So...if a belt tension ,is say, over tight for 70,000 miles and a new belt is put on that is under tightened but within acceptable limits for 10,000 miles, the difference in lateral shaft tension won’t affect the pulley shaft and thus the bearings in any way? Is the construction of the component that good that in no way can a difference in belt tension be detrimental in some cases ? A simple yes or no will do. Let’s wrap this up.. My head is starting to hurt.

Maybe the scenario of failure I referred to had the belt really loose but the owner didn’t notice any squeal for 70,000 miles and then put on a belt too tight. Jbrant?

 

CITE YOUR SOURCES.

You got an answer 7 posts ago but don't want to accept it.

 

Bearings don’t have memory. There’s no way a looser belt would cause failure.

An overly tight belt can cause bearing wear, but that would be independent of the previous belt tension.

 

In other words, the component can handle changes in lateral movement caused by differing belt tensions, no matter if they are somewhat extreme or not. I can buy that. I guess the instances of a belt tension being altered and causing damage are unfounded. Urban myth on my part maybe. Urban myths happen. I guess I stand corrected. Sorry if I got a bit contentious. I may have been coming from urban myth. That happens. Oh, btw..what are belt tensioner gauges used for???!!! ( forget you, never heard of them, never used one).

 

And here's the video:

https://www.youtube.com/embed/Zi1XfFUOjKc

 

Such a simple answered to myself. Pull the belt a few times and muscle memory the tension with the new belt. Not sure why I got into the mechanics like I did.
You got me, urban ledge maybe. I swear I heard of it happening.

 

No, you misunderstood what I was getting at.

The "new" (reduced) tension is not what causes the part to go bad.

Having a belt that's too tight causes the part to wear out prematurely, putting a new belt on is irrelevant. The wear and tear is already done. A belt that's too loose just squeaks and doesn't add excess wear and tear.

Correct. When I said it "continues to exacerbate the problem" I was talking about continuing to use a part that is already worn out. It has nothing to do with the reduced tension of the new belt.

 

Like saying I got in a car wreck after I filled up with gas, so obviously filling your tank with gas causes car wrecks.

 

couple things about tagging members. 1) put the "@" at the beginning of the screen name, and 2) it helps to also spell it correctly...

NO.

The belting being too tight for 70k miles is what did the damage. Putting on a new belt, even at the proper tension using a proper gauge doesn't fix that.