Thread: How To Measure A Vee Belt

Good question, I think inside but if you measure it then either take it with you or measure one with the length on it you should be able to work it out.

A V belt should not go all the way to the bottom of the pulley. The outside edge will actually sit slightly above the edge of the pulley when it is new. It transmits the power along the edge of the V belt.

In answer to your question...I don't know. I have replaced and adjusted many, but they still had the size marked on them.

If you had adjustment available, there wouldn't be much difference to either measurement method I would imagine. Perhaps the average would be sufficient?

Inside from what I remember but If you have the old one don't rely on it too much as it will have stretched in use, run a bit of string around the pullies where the belt will run cut it to length and then compare it to the new belts inside diam , an easy double check. Just make sure the motor to compressor is at the closest setting so that you can slide the motor back if the belt stretches
Rgds
Russell

oops, forgot. The old belt will have stretched...

Hi,What I do is use telecom rope or draw rope ,run it around the distance and buy the one that fits that best setting the motor mount to allow the full movement back first,then make a deal with the supplier to come back and swap if there is an error.Works for me in the designing building the so many workshop resurrected machines and a great variety of motors.I have saved a lot of money buying auto vees,they often have a special so I have shopped around there first.Places like super cheap etc have a measuring device in store to give you the size from the piece of rope.

Another arrangement if you live a long way from the supplier is to make a deal and get three belts one under,one correct and one over the rope size with a right of return and credit. The rope kicks off the base of the pulley and gives a more accurate measure in the first instance.

Trust you have dried out now and have success. Peter

According to Machinery's Handbook, belt length is measured on the outside of the belt. Most V-belts have the reinforcing cords (non-stretch) near the outside face, so the pitch length is substantially the same as the outside length.

Best not to use the absolutely closest setting for measuring the length, because you need that to place the loose belt on the sheaves without distorting it too much. Allow about 1/2 to 1 times the belt width for initial take-up.

Joe

Graham, If you measure the outside diameters of the pulleys, and also the distance from the c/s of the two shafts, and give this info to any decent supplier, they will give you the correct belt. There are also a few belt length calculators on the net. Just input belt section type.... ie. a, be section etc, and the above data, and the program spits out your belt.

I have the Gates programs on my pc, so if you post the data, I will respond asap.

I replace about 3 or 4 belts a year on my farm machinery. I measure the outside diameter with an allowance for stretch (which varies with the quality of belt).

I would get it right 4 times out of 5.

If you have the old belts, you could cut them and then measure the overall length!

Depends on the brand of belt. If the cogs are on the inside, measure the outside. Some have their cogs on the outside (Dayco), measure the inside. Most industrial belts don't have cogs, so measure the outside.

As penpal said too, at autObarn we had a belt measure that we could get a pretty good idea of both length and width, But allow for the old belt being slightly stretched.

Thanks Fossil,

The major pulley OD is 200mm,The minor pulley 70 with centers 295mm (closed up measurement ) with about 25mm of horizontal adjustment.

There was a faint number embossed in yellow on both the belts which was VA 582.

Geez only lasted 30 years old you think a set of belts should last longer than than that.Actually there not worn at all except for a little straggly bit on the top surface of one.

What do you reckon for the replacements? 30 months ?

Thanks
Grahame

30 years is doing very well.

One of my compressors is a peerless 15cfm twin, which I bought in 89.
I replaced the belt last year and I though I was doing well.

As far as belts go...... tight dimension supplied.... the calculator comes up with 1028mm or 40.5".
Seeing as you have 25mm of adjustment, I would go with a 41" belt... so that means you are after an A41. (I assume the pulleys are "A" section which is the case with 99.9999978% of compressors that size)
If you get a decent brand of belt, Gates or similar Yankee stuff , stretch will not be a problem. Expect to pay $20.00 for a really good belt, and 1/2 that for a POS belt.

It's good to hear you getting on with things after the floods.

Take care.

Thanks Foss

You are a national treasure.
I put the motor on but have to take it off again.The electrician didn't put the pulley back in the right spot on the motor shaft.
As I have longitudinal but not lateral adjustment. The pulleys or belts will not align and that will bugger the belts quick smart. Back to the electrician.
I will do it properly and hunt up some Yankee belts and new filter medium and bugger it, new oil as well.Should be good for another 20 years.

Thanks again
Grahame

To align the pulleys, hold a bit of string along the edge of one pulley, then move the other end of the string towards the second pulley along the horizontal axis. What you are trying to do is when you move the string towards the edge of the second pulley, the string should touch both sides of the second pulley at the same time.

That is how I used to do it, but these days i'm sure people use lasers.

I have confused myself when I read the above, but it is really simple - just use some builders string.

To be fair, the leccy only had the motor I had sent in.
Any way his piece of string wasn't long enough to reach my place.
I use a straight edge.
Generally there is a dull and a shiny patch on the shaft and I always match the pulley depth to that unless given other specific data.
Pulley position -on the shaft - was important in this case as the motor had no provision for side ways adjustment.

I haven't looked but there will be a key way and grubscrew ( I hope)
Grahame