Installation, alignment and tensioning

Safety first

1. Isolate and lock out the motor at the isolator, tag it, and try to start it to prove it's dead.
2. Release stored energy: let flywheels and fans stop; block anything that can turn under gravity, wind (fans) or process pressure (pumps); release pneumatic or spring tensioners.
3. Remove the guard only after isolation. Keep it with the machine.

Removing old belts

• Slacken the motor base or tensioner until the belts come off by hand. Never prise belts off (or on) with a screwdriver or bar: it breaks the tensile cords and chips the pulley.
• Before throwing them away, look at the old belts: wear patterns tell you what was wrong. See troubleshooting.
• Replace all belts in a multi-belt drive at once. Old belts have stretched; a new belt in an old set carries most of the load and fails early.

Inspect the pulleys

• Groove wear: use a groove gauge for the section. A shiny groove bottom, a belt riding low, or "dished" sidewalls (light visible between gauge and groove wall) means the pulley must be replaced. New belts in worn grooves last a fraction of their normal life.
• Damage: chipped flanges, cracks, burrs or rust on the groove walls.
• Fit on the shaft: taper bush screws at the right torque, key in place, no wobble.
• Clean grooves of rust, oil and rubber dust with a dry cloth or wire brush. Don't use solvents that leave a film.

More: pulley wear and gauging.

Fitting new belts

1. Check the belts: correct section and length, and from the same matched set (same matching code or made to match).
2. Move the motor in until the belts slip into the grooves by hand, with all belts on the same side (slack on the same side).
3. Take up the slack evenly. Keep the motor square: adjust both jack-screws equally.
4. Align (next section), then tension.

Alignment

There are three ways a drive can be out:

Tools

• Straight edge or taut string across both pulley faces (allow for different pulley face widths: measure from the groove centres).
• Laser alignment tool that clips into the groove: faster and more accurate, and shows all three errors at once. Worth it on any critical or large drive.

Fix twist first (shim the motor feet, check for soft foot), then angular, then parallel (slide the pulley on the shaft or move the motor).

Tensioning

Too slack and belts slip, glaze, burn and squeal. Too tight and you overload motor and machine bearings, bend shafts and stretch belts. Rules of thumb ("an inch of play", "until it stops squealing") get it wrong in both directions. Measure it.

Method 1: force-deflection (tension gauge or spring balance)

1. Measure the span length t (the free length between the pulley tangent points).
2. The deflection to use is 1/64 of the span: 16 mm per metre.
3. At mid-span, push one belt at right angles to the span with the gauge and read the force when it has moved that far (lay a straight edge across the belts as a reference).
4. Compare with the target force from the maker's table or the tension calculator. Below target: tighten. Above about 1.5× target: slacken.
5. Check every belt in the set; on banded belts push the whole band and use the force for the number of ribs.

Method 2: frequency (sonic tension meter)

Pluck the span and measure its natural frequency with a sonic meter or a vibration app. It's repeatable, needs no force, and suits short spans and timing belts.

Use the frequency calculator to turn a target tension into a target frequency.

Method 3: elongation

Mark two lines a measured distance apart on the slack belt and tension until the distance grows by the maker's stated percentage. Common on flat belts and some round PU belts.

Run-in and re-tension

• New V-belts bed into the grooves and lose tension quickly. Many makers set new belts higher (about 1.3× the running value), then re-check after 4 to 24 hours of running and re-tension to the running value.
• Check again after the first week, then on the normal schedule (maintenance).
• Lock the motor base after every adjustment.

Timing belts: what's different

• Never crimp or kink a timing belt: bending it tighter than its minimum pulley diameter breaks the tensile cords invisibly.
• Fit the belt over the pulleys by moving the centres, not by walking it over a flange.
• Alignment ≈ ¼°. Flanged pulleys keep the belt on, but rubbing on a flange means misalignment.
• Tension to the maker's figure. Over-tension makes timing belts whine and wears the teeth; under-tension lets them ratchet (jump teeth) under load.
• No run-in re-tension is usually needed, but check after the first day on heavy drives.

Guarding (South Africa)

The Driven Machinery Regulations, 2015 (Notice R.540 under the Occupational Health and Safety Act, 85 of 1993, in force since 30 September 2015), regulation 3, requires users to:

• fence or guard shafts, pulleys, wheels, gears, sprockets, couplings and similar revolving parts;
• countersink, enclose or guard set screws, keys and bolts on revolving parts such as pulleys;
• guard driving belts, ropes and chains;
• guard the underside of overhead belts above passages or workplaces so a broken belt can't fall on people (an inspector may waive this for light, slow belts).

Use mesh guards that let you see and check the drive, with openings sized so fingers can't reach in-running nips. Leave room to measure tension through an access panel.

Summary only. Check the current regulations and your plant's safety rules.

Commissioning checklist

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