Timing Belt

The drive belt on my sander has disintegrated. I haven’t checked with the manufacturer of the machine yet but others have been quoted nearly £30 which seems a bit excessive! How are toothed belts sized? The pulleys are about 22mm wide so I’m guessing the belt was 19 or 20mm, the centre to centre of the teeth is about 7.5 - 8mm and if I wrap a tape measure around both pulleys I get an overall length of 575mm. I can’t seem to find anything this size. I note there is mention of the number of teeth on some websites but I have no idea as there’s nothing left of the old belt but bits! Any ideas?

Tooth pitch is also important. Some companies will cut a belt down to the required width.

Width can be measured by width of pulley.

Measure the tooth pitch from centre to centre of the raised parts on the pulley, look on the web for details of type of belt and way to determine length required, usually by number of teeth needed to fit over the pulleys in a working position.

Emgee

Edited By Emgee on 13/06/2022 22:18:29

Get some info on belts and pulleys here.

**LINK**

Edited By Emgee on 13/06/2022 22:31:14

Vic

If you want to reverse engineer the belt you need to track down a belt manufacturers catalogue that gives the formulae to calculate belt length for a given centre to centre distance and type of belt. Last time I did this I used formulae from ContiTech HDT belt catalogue that I'd downloaded. I imagine Gates and others have equally useful catalogues.

Doesn't help that its often not clear from the pulleys which type of belt you have. Usually easy enough if you can eyeball a belt, use the magnifier or photo app on a smartphone to give a better view of a small tooth profile.

Hand held sanders, planers et al have fixed centre distances so the belts are self tensioned by stretching.

A standard near equivalent may not stretch correctly to give the right tension. As the tension is intended to be set by centre distance adjustment the standard belt can be stiffer.

Certainly the semi-transparent ones I got for my planer last year were somewhat more elastic than a standard belt of similar size. As in your case the makers official part price was expensive but diligent searching found two for two-thirds the price on E-Bay. On flogging through all the lists I found that there are only about 3 or 4 sizes of belts used on hand held planers. Presumably because most of them are pretty much different coloured iterations of same design from China Inc.

Clive

Have a look at solenttools.co.uk. They have belts for all types of machinery.

Got a belt for an obscure Wicks sander from them

Peter

try ebay there's loads on there: sander drive belt: Search Result | eBay

Edited By Juddy on 14/06/2022 10:37:52

“How are toothed belts sized?”

Generally pitch, width &number of teeth, but it’s a minefield: tooth profile also matters, and there are many. Pitch could be imperial or metric (0.2” is very close to 5mm, for example. )

Can you discern any numbers on the remains of the old belt?

Edited By Andy_G on 14/06/2022 11:27:37

Seven or so replies to Vic's question and nobody has given him the details of the belt he needs!

I wonder if its because we dont know the model number of the sander?

Since Vic already has a price for the belt then whoever quoted must have more info than we do.

Ian P

Take the remains of the belt into your local bearing supplier. they often stock a range of belts, Vee, Polyvee and toothed

They should be able to tell pretty quickly what type of belt it is, and you can then ask for a belt of the length that you require.

Timing belt quality can vary, so choose the best that you can get, and make a note of the type and length, in case it is ever needed in the future..

A lot of diesel cars required belt changes after as little as 30,000 miles, while one other engine, (Perkins Prima ) the recommended change was at 70,000. But I never heard of a failure! (And I have tried to fail one. From memory the supplier was Gates )

Just as well as on an engine, a timing belt failure usually resulted in such damage that repair was uneconomic.

Howard

It is possible to identify a replacement belt in a situation where the tooth profile, the pitch, the width and the length are unknown but it requires a bit of effort. (jump to last paragraph for the easy way)

There are quite a few different tooth profiles and whilst they may appear similar picking the wrong one will significantly belt life. Manufacturers catalogues might show detailed drawings of the tooth profile but if the pulleys are fitted with flanges and the tooth profile is not visible then its hard to compare and decide.

I imagine that as Vic's belt is on a sander then it will probably not have any means of adjusting the pulley to pulley centre distance, therefore its essential to get the exact length of belt. one can work out the length if one can measure the pulley centres accurately but that is not always as easy as it seems.

Measuring the belt pitch by counting the number of teeth on a sprocket which you know the diameter of is straightforward, so in conjunction with centre to centre distances you can consult catalogues and most likely identify what will fit.

Far, far easier than measuring and guessing is just to Google spares with the product model number, most likely some of the results will include the actual belt manufacturers part number which you can then use to 'shop around' to find the best value supplier.

Ian P

Thanks for your thoughts so far. The machine is a Record Power BDS250. There are lots of belts for the smaller BDS150 on eBay etc but nothing for my machine. It seems that SIP tools also sell this machine and the price from them is a bit cheaper at around £17, but is it exactly the same? The old belt, if it makes any difference was a translucent pale brown colour as I remember. The pulleys have square teeth so that discounts some of the belts I’ve seen with rounded teeth.

The belt is adjustable by the way.

Edited By Vic on 14/06/2022 16:19:39

Apart from the reinforcing cord that got wrapped round the pulley, I hoovered the rest of it up with my shop vac!

I doubt even Basil Rathbone would be able to identify it beyond “yes, it was a timing belt Watson”!

Vic

Translucent belts are generally "stretchy" so they can be assembled onto pulley pairs at fixed centre distances and seem to carry a premium price. All too often they are specials of a non standard length with no direct equivalent in the normal black belts.

As your motor is adjustable a standard black belt will do fine so long as its a standard length. If I recall things correctly my Draper badged version of the smaller Record sander also had tension adjustment and was fitted with a black belt but the length was non standard so I still had to pay OEM prices.

Clive

This is what the setup looks like. You loosen the four bolts and the whole assembly goes up and down. I’ve sent a message to RP asking how much a replacement belt is.

By a process of elimination I think I may have found something. I took a measurement of 575mm long and 576mm seems to be a standard length. Pitch and width also seem about right. I quite like the price as well. Postage is £4.99.