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Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
Peter, I just tighten them so they have about 1/2" of play when pressed on. It's tight enough not to slip or squeal, but not too tight to cause problems.
Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
Peter, you don't have to press too hard; maybe a force of around 10lbs?? If it's loose you can tell that right away with any pressure. If it's so tight you can bounce kids on it like a trampoline??? Waaay too tight. Same idea as what Eric mentioned. Pulling up or pushing down = same results. I usually push down simply because it's the flat spot on the belt and I've always done it that way.
I've never worried about the actual belt tension in my 40 years of working on cars. I have always used the 1/2-inch maximum deflection rule of thumb without a problem, and I don't have a belt tension measuring tool, anyway.
But I did wonder if tension specs are available in the chassis service manuals. I couldn't find anything in the '73 manual I have, even though it says, whenever a belt is mentioned, to tighten them "to specifications" with tool such-and-such.
I did, however, find a belt tension chart in the '78 manual I have. Interesting that it depends on belt width.
A friend of mine brought my attention to page 91, section 6-1 of the 1970 Assembly Manual, where it clearly states for new belts tension, 110-125lbs, used, belt min 70lbs.
I must have looked at that page 20 times but did not see it.
With a used belt tension spec of min 70lbs, I can see why a rule of thumb test is acceptable.
Neither have I, and I'm guessing neither has 99.999% of the rest of the universe. Unless you own a garage and install fan belts for a living, a tension gauge is overkill. The 1/2-inch deflection rule is all the shade-tree mechanic needs. As I said earlier, it's all I've ever used in 40+ years of playing with cars, and I've never had a problem with too loose or too tight fan belts.
I'll bet that half the professional mechanics out there don't bother with a gauge, either. Put on the new belt, tighten to maximum 1/2-inch deflection, and out the door the car goes.
Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
I don't know Eric, I don't think even the factory used the tool. They likely just wanted the car out the door too, and just used the 1/2" deflection method too. Not everyone follows the guidelines in the AM that engineers provided. Sometimes ya got to fly by the seat of your pants. And that works pretty well 99.9% of the time IMO.
Thanks Eric Actually I can see how the thumb method works since in pretty much all that I have found out about different vehicle tension spec, there was always a pretty big margin for a used belt tension.
About 7 years ago, I was setting up the Toyota plant in Mississippi. This was just after GM left NUMMI (we here on this site call it Oldsmobile Fremont Assembly) and we had to close NUMMI after offering the entire workforce jobs at other plants, which most didn't take due to having to move and I don't blame them.
Toyota salvaged some production equipment, and some of the "car line" equipment (as opposed to truck line) came to MS, and I got a REALLY OLD air over hydro hydraulic cylinder ram with which to tension the serp belt on the Corolla. The 2ZR engine had a serp belt, but no tensioner, you adjusted the alternator out until it was tight and ran it down.
So this thing worked by one detail on the crank pulley, and one detail on the alternator, put both hands on the handles, push both buttons at the same time, and WHAM, you had yourself ~1200 psi. (It was a 12:1 air over hydro running at plant air of 100 psi.) Leave it engaged, run the bolts down, release it, and move on.
That thing does every Mississippi Corolla, or it did since the last time I was down there.
Quality came out with this little device. It had two forks and a ram between them. Put the belt on top of the forks, and then push the ram down a certain distance, and it would measure the force and figure tension. I do remember having to crank up the pressure some on the hydraulic pump since they were initially not satisfied.
Serp belt, not V, not on an Olds, but I hope a factory story was mildly entertaining on the subject at hand.
there was always a pretty big margin for a used belt tension.
You're absolutely right. Look at the specs in the chart I posted earlier on.
80 lbs new, 50 lbs used
150 lbs new, 70 lbs used
Those are big differences.
When does a new belt become "used," anyway? After 2 miles of driving? 10 miles? 100 miles? 1000 miles? Or is based on time? After a day? A month? A year? In other words, when do you change over and start using the used belt spec instead of the new belt spec? The belt, after all, is in constant tension, not just when the engine is running or when the car is moving, so mileage is not really an accurate measure of age or how used up a belt might be. And belts transition from "new" to "used" gradually, not in a single, huge step as they slowly stretch (or actually, as the mechanical engineers would say, relax) with time.
Given that back in the day the service recommendation might have been to replace the belts every 12 months, the spec might have said something like "0 to 3 months old, 80 lbs," "3 to 6 months old, 70 lbs," "6 to 9 months old, 60 lbs," "9 to 12 months old, 50 lbs," "more than 12 months old, replace." But no would have paid that close attention to belt tension, then or now.
The way I look at those numbers, if I have a gauge and the belts are more than 10 minutes old, I'll use the lower number.
June 28th, 2018, 09:43 AM
Actually I can see how the thumb method works since in pretty much all that I have found out about different vehicle tension spec, there was always a pretty big margin for a used belt tension.
