Free gauge indicates worn - and inefficient - pulleys

ERIKSvisit website


Efficient operation of V and wedge belt drive systems depends on both the belts and the pulleys being in good condition. Users of V and wedge belt drives are generally aware that the belts need replacing on average every three years but, since pulleys are made from cast iron, maintenance engineers often assume that they do not wear and they therefore tend to be overlooked.

Worn pulley grooves, however, can be the direct cause of more frequent belt replacements and significant falls in energy efficiency. Although they wear more slowly than belts, once a pulley groove is out of shape it can result in belt slippage, which, in turn, causes accelerated wear in both components; the wear rate then becomes exponential.

Using a Fenner Pulley Groove Gauge, maintenance staff can quickly determine if pulley grooves are worn or not, allowing them to make an informed and swift decision on whether to renew the pulley.

The efficiency differential

The most noticeable effect of pulley groove wear is rapid belt wear and deterioration. But before that point is reached, the belt drive efficiency will have reduced dramatically; in basic terms, slippage = speed loss, and speed loss = inefficiency and lost energy.

As an example, a 37kW electric motor running continuously at an average electricity tariff of £0.06/kWh will cost £17,250 per year to run. Poor pulley groove condition can easily waste 10 per cent of the energy input into the unit; wasted energy will therefore amount to £1750 per annum. Replacement pulleys for this system would have an ROI period of less than two months, and companies with an energy saving target could add the efficiency improvement to their target.

How to test pulleys for wear using a Fenner Groove Gauge

A Fenner pulley groove gauge is very simple to use. There are eight size measures on each key ring comprising two sets of four basic sections. Best fit for pulleys of different sizes depends on the bend radius of the belt, so larger pulleys (eg over 190mm diameter for SPB groove section) require a groove angle of 38degrees and smaller ones 34degrees. There are two star-shaped gauges on each key ring, one for larger pulleys and one for smaller pulleys.

Simply clean a section of pulley and insert the appropriate gauge profile into the groove. If there is a 5 per cent or greater wear at the pitch-line of the pulley, then the pulley needs replacing. The pitch-line is one-third of the way down from the top of the pulley where the stiffer load-bearing cord section of the belt rests.

A good rule of thumb is: 'the point should be well clear of the bottom of the pulley groove and no daylight clearly visible on either side of the gauge.' Pulley grooves tend to wear round, so when the straight-edged trapezoid shape of the gauge is in the groove, the rounded wear will show on either side.

As a result of worn pulley groove flanks, the belt sits further down the pulley and is therefore slacker, hence the slippage. There is normally some adjustment in a belt drive system to account for a degree of slack, but there are two limiting factors: if belts become slack and start to wear, the profile changes and they become inefficient. As grooves change from flat-sided to curved-sided, and the belt gets as far as the bottom of the groove, there is no wedging mechanism and the belts will slip and wear very quickly. Using cogged belts does help, even with pulleys in poor condition, but the ultimate answer is pulley replacement.


Put simply, there are tens of thousands of pulley-driven pumps, fans, conveyors and machines in use in the UK, many of which will be worn and operating inefficiently. A free Fenner Pulley Groove Gauge could save thousands of pounds in energy efficiency improvements when used to check pulley groove wear. Belts may need to be removed to check pulley grooves, but it is generally possible to get a good measure by simply removing all or part of the drive guard. Sensible safety precautions (such as turning the drive off) before using the gauge should also be observed.

Replacement Fenner belts and pulleys are available from both independent stockists and at any one of the 170 WYKO branches located throughout the UK.

Meanwhile, contact Wyko direct at to request your free Fenner Pulley Groove Gauge.

© Copyright 2006-14 The Engineering Network Ltd.