Belt Tension

[A.K. Boomer]

Some glass fibers have small or even negative coefficient of thermal expansion in the longitudinal direction. If glass is used for reinforcement of automotive drive belts, it's entirely possible that the belts will be tighter at operating temperature because the engine expands more than the belt.

So, are you tensioning your belts at operating temperature?

Yes, NEGATIVE coefficient of thermal expansion in the longitudinal direction. Bulk thermal expansion coefficient remains positive. I don't know what reinforcement fibers are used in any particular application. Just something to be aware of.

Spoken from one of the deeper thinkers, good write-up,

now toss in aluminum block and heads...

And i have total proof of your theory,

Earlier honda's had square tooth timing belts, aluminum block and heads though, square tooth belts are notorious for "barking at you" if too tight, it actually creates a "mismatch" in the engagement tooth/pitch, hound dogs have since gotten away from them for that reason, But --- if you had a borderline tensioned timing belt leaning to the tight side, all could be fine when engine is cool and upon start up, but then as soon as it's warm you hear a drastic "rubbing" sound kinda fretting away, and yeah it's because the engine outgrew the damn belt....

[strokersix]

Some glass fibers have small or even negative coefficient of thermal expansion in the longitudinal direction. If glass is used for reinforcement of automotive drive belts, it's entirely possible that the belts will be tighter at operating temperature because the engine expands more than the belt.

So, are you tensioning your belts at operating temperature?

Yes, NEGATIVE coefficient of thermal expansion in the longitudinal direction. Bulk thermal expansion coefficient remains positive. I don't know what reinforcement fibers are used in any particular application. Just something to be aware of.

[Bob Engelhardt]

According to IR, the deflection is proportional to the span (1/64" per inch), with the specified force. For V belts.

That varies drastically,on one of my big grain augers it has 3-315” belts which I run very tight and have had good success.They sit out side in the elements and I’m on 2nd set since 1990.

The IR spec was taken from their Type 30 compressor manual. I.e., probably in consideration of its bearings. Absent specific directions, it would be a good rule for another compressor. Or bearings in a similar setup.

[Tundra Twin Track]

According to IR, the deflection is proportional to the span (1/64" per inch), with the specified force. For V belts.

That varies drastically,on one of my big grain augers it has 3-315” belts which I run very tight and have had good success.They sit out side in the elements and I’m on 2nd set since 1990.

[Paul Alciatore]

This is what I was told many years ago and it is probably a good "rule of thumb". It does work in many cases.

But when belt tension is critical, a lot of OEMs will specify some method of measuring the belt tension. And there are tension gauges for this. They also use deflection, but in a controlled way. When I have the information for an exact tension I do try to use an appropriate tension gauge.

Other times you have to just use the rule of thumb AND THEN, observe the system's operation and make further adjustments as needed. I would not start at the "gorilla" point. But not with the belt flopping around either. Moderation in all things!

No roasting here. I just go by the deflection of the belt when pressed in the middle of the "span". For most that are a foot or so span, that's about a half inch or a bit less for v-belts.

I usually do not measure, but go by the pressure to deflect.

They will probably roast both of us.

[The Artful Bodger]

Bodger,

Doesn't twisting the belt make the thresher run backwards and mix the wheat back in with the chaff?

Ian

There is a lever on the traction engine where we can select 'grain' or 'chaff' to meet market needs.

[Bob Engelhardt]

Deflection of the belt in the middle of the pulleys of about the width of the belt.

According to IR, the deflection is proportional to the span (1/64" per inch), with the specified force. For V belts.

[A.K. Boomer]

Deflection of the belt in the middle of the pulleys of about the width of the belt.

Deflection middle of the pulleys but how much pressure? and width of the belt of what ? a multi-rib serpentine?, some are 3 or 4 or even 6 or more ribs, and in the middle of the pulleys is a pretty broad statement depending on machine/engine design and span...

You can find Info in most cases per exact piece of equipment because they are taking all of it into consideration, another factor? overall belt length due to belts having elasticity so drive components putting demands on the drive side of an extra long belt can really have a loosening effect on the other side...

[Robg]

Deflection of the belt in the middle of the pulleys of about the width of the belt.

[Ian B]

Bodger,

Doesn't twisting the belt make the thresher run backwards and mix the wheat back in with the chaff?

Ian

[The Artful Bodger]

We usually run the threshing mill with a straight belt but in windy conditions we twist the belt.

[55fairlane]

A belt tension gauge is well worth the money, but most service guys won't know what to tell ya......some wire possessing machines you use a tuning fork to know if the belt is exseive loose or tight...PIA

[BCRider]

....I always error to the side of less due to it being just fine and most thing's handling it and the bennies of longer component life,

however - you can actually go too loose even if slipping does not occur, you don't want the belt going through traumatic fluttering stages destroying itself.....

That sounds like it's just right. It's pretty obvious when they are too loose by the flutter. So tight enough to not flutter and that's dandy.

[Glug]

Those acoustic belt tension measurement gizmos look neat. The twang of the belt determines the tension, like a guitar tuner, but way more expensive.

[A.K. Boomer]

So much depends on belt design too, serpentine or standard, If not auto-tensioned I just put my two cent's on it - I always error to the side of less due to it being just fine and most thing's handling it and the bennies of longer component life,

however - you can actually go too loose even if slipping does not occur, you don't want the belt going through traumatic fluttering stages destroying itself...

When I took the A/C system out of the Peashooter the AC shared the same pulley runs as the water pump, it was a 5 rib serp. after the compressor was removed all that had to be driven was the water pump. and the belt option they give is of course way shorter, yet still 5 rib, to further save fuel I sliced the 5 rib lengthwise into a 3, and ran it very loose, however - upon giving the engine a few revs noticed the belt going into drastic flutter mode at certain RPM's so snugged it back up some - still loose cuz alls it's doing is driving a water pump but tight enough to stabilize it...