Looking at the photo … I can only suggest you overlay the two belts and compare them directly … the old one certainly looks longer to me.

MichaelG.

What are the markings on the belts? Usually they will tell you the belt section, and the length (A35)

BS Au1440 deals with Vee belts.

One advice on measuring the length of A Section Vee belts is to measure  the OUTSIDE length and subtract t 2 inches. (Tameson), B section -3″, Z section -1.5″

It may be that by quoting the internal lenghth, you have been supplied with a belt of that OUTSIDE length.

Measure and quote the OUTSIDE length, in both Inches and mm, and you may get bthe length of belt that you require.

Howard

Hi, these are all the standard vee belt sections with their sizes.

There are other non-standard sizes as well though.

Regards Nick.

On 8 November 2023 at 19:22 Steve355 Said:

The problem is, the original belt is so old and worn, it has no markings and it’s difficult to tell what profile it originally had. It was an “a” of some sort but the dimensions vary wildly around the circumference.

I think I’m going to put the new belt back on, and if it doesn’t magically correct itself, make a guess at how short it is and order another.

You shouldn’t need to guess the length really. If the motor table needs to be, say 2″ lower, just order a belt 4″ longer than the one you have.

According to Tony, the original might have been a linked belt anyway;

Drive came from a motor mounted on a hinged plate in the base of the column, an excessively long and whip-prone Brammer (sectional) belt being used to transmit the drive to the spindle. The whip can be countered by using a PowerTwist belt which, because it lacks metal pins, gives a softer drive and can accept a mid-position belt tensioner consisting of two pulleys acting to spread the belt apart, with a left and right-hand threaded adjusting rod half way up the column (an easily contrived amateur modification). 

They can sometimes wear the pulleys slightly oddly, and cause a problem if the belt or the pulley wears enough for the metal bits to bottom out.

If the pulley is worn, such that the belt sits low, you might be better off with an A section belt, rather than an SPA as they are a bit shallower and less likely to bottom out in a slightly wider pulley groove.

There’s lots of useful info on This Site, amongst others

Bill

On 8 November 2023 at 22:24 Steve355 Said:

No… if you look on the pic above, the bolt hole needs to move down about 10cm so it can be bolted to the slot. So I guess the belt needs to be about 20cm longer. Which sounds like a lot. Must be right though I suppose.

Sincere apologies for daring to doubt you

… in my defence: We have already seen that ‘perspective’ photographs can be misleading.

MichaelG.

Like Michael I had also unwitingly asumed it was 10mm, I had read it that way and only Michaels comment caused me to check, I’m worse than I thought ! Worn pulleys can cause belt length and identity issues. If you know what belt you now have then adding 2x the missing length to reach the adjustment should put you in the ball park and since we now know there is good adjustment it will not be too critical. As for my guess at A90 or A91 forget both of them ! Depending where you are most transmission specialists will be found helpful, just take in what you have and they will match it up – for me the Hayley group in east anglia.

Or make a link for the adjuster ?      Good luck, Noel.

On 8 November 2023 at 20:24 Steve355 Said:

It’s annoyingly close…. It may simply be that the old belt stretches slightly under the weight of the motor.

 

Hi,  I think that 10cm is annoyingly a long way out, which is equal too 3.937 inch’s.

Regards Nick.