Gear Coupling Installation and Alignment Checklist

Step-by-step gear coupling installation: hub fitting, alignment targets, hub gap by FG size, first grease fill, start-up checks and troubleshooting.

Short answer: install a gear coupling in this order — inspect the coupling and both shafts, fit the hubs at the catalogue gap between hub faces, align the shafts with a dial indicator before the sleeve goes on, fill with coupling grease, engage and centre the sleeve, turn the drive by hand, then re-check alignment once the machine is at running temperature.

Shaft alignment is the single largest factor in gear coupling service life, so it gets the most space below.

The checklist follows the order the work is done on site, with the figures to aim for and the readings to record. Grease grades are covered in our gear coupling grease lubrication guide, and everything after commissioning — inspections, re-greasing and records — in the gear coupling maintenance schedule template.

Pre-Installation Checklist

Equipment Verification

• Verify the coupling size against the design torque: motor torque T (Nm) = 9550 × P (kW) ÷ n (rpm), multiplied by the service factor for the duty. The gear coupling torque calculator does this from the motor nameplate.
• Confirm the hub bores match the shafts. SMI machines bores to H7 unless you specify otherwise; whether that gives a clearance, transition or interference fit depends on the shaft tolerance, so check which before choosing between cold and hot mounting below.
• Check the keyways: the key should be a snug push fit in both shaft and hub, not loose.
• Inspect the gear teeth for shipping damage — scoring, nicks or damaged tooth tips.
• Check the sleeve's internal teeth for machining burrs that would stop full engagement.
• Verify all components are present: both hubs, the sleeve or sleeves, gasket, end seals, bolts and grease plugs.

Shaft Preparation

• Clean the shafts thoroughly — remove rust, oil, paint, burrs and nicks.
• Verify the shaft diameters are within tolerance; our guide to measuring a shaft and selecting the bore and key shows how.
• Apply a thin film of light oil or anti-fretting compound to the shaft before fitting.

Tool Preparation

• Oven or induction heater for hot mounting (interference fits only)
• Temperature measuring device
• Hydraulic press or hub fitting tool — not a hammer
• Alignment tools: dial indicators or a laser system
• Shims for the machine feet
• Torque wrench for fasteners
• Coupling grease and filling equipment
• Paint marker

Hub Installation

Never hammer a hub onto a shaft. A blow on the hub face sends a shock through the gear teeth that can crack tooth tips or start micro-fractures. Press the hub on for a clearance fit, or heat it for an interference fit.

Interference Fit (Hot Mounting)

1. Calculate the heating temperature

   • Temperature rise (°C) = (interference × 1000) ÷ (bore × α), with the interference in µm, the bore in mm and α, the coefficient of thermal expansion, in µm per metre per °C (about 11–13 for steel).
   • Example: a 50 µm interference on a 100 mm bore with α = 12 needs 50 × 1000 ÷ (100 × 12) ≈ 42°C just to cancel the interference.
   • In practice the rise is typically 80–120°C above ambient, more than that minimum, so the hub slides on freely.

2. Heat the hub uniformly

   • Use an oven or induction heater
   • Never use an open flame on the bore
   • Verify the temperature has been reached

3. Mount quickly

   • Position the hub immediately
   • Slide it to the correct axial position (see gap G below)
   • Insert the key before the hub cools
   • Hold it in position until it has cooled

4. Verify the mounting

   • Check the axial position
   • Confirm the key is properly seated
   • Allow the hub to cool completely before aligning

Clearance Fit (Cold Mounting)

1. Apply retaining compound if specified, otherwise a light oil film
2. Slide or press the hub onto the shaft — use a hydraulic press or hub fitting tool if it is tight, never a hammer on the hub face
3. Fit the key — flush with the hub face or slightly below; it must not protrude
4. Position the hub axially per the drawing, at the correct shaft engagement length, leaving gap G between the hub faces
5. Secure the hub with its retaining device — set screw, circlip, or shaft-end washer and bolt
6. Tighten to the specified torque — a thread-locking compound alone is not enough; the hub needs mechanical retention

Alignment Procedure

Align the shafts before the sleeve goes on. Never use the sleeve to pull misaligned shafts together, and never tighten coupling bolts to force alignment: whatever misalignment is left is carried by the gear teeth and the shaft bearings for as long as the drive runs, and it causes early failure.

Rough Alignment

• Position the equipment approximately in line
• Check every machine foot for soft foot and shim it before taking any alignment readings
• Achieve rough alignment visually
• Secure the equipment loosely

Final Alignment

Measure with dial indicators or a laser system, and correct by shimming the motor feet or moving the machine. SMI's recommended targets at assembly are:

Two conversions help when a laser system or a drawing states the tolerance another way. The angle, in radians, is the face TIR divided by the diameter the indicator tip sweeps: 0.10 mm over a 200 mm sweep is 0.0005 rad, about 0.03°. A rim reading is twice the actual centreline offset, so 0.05 mm TIR means the shaft centrelines are 0.025 mm apart.

Angular Alignment

1. Mount the dial indicator on the hub face
2. Read TIR at four points 90° apart
3. Calculate the angular deviation
4. Shim or move the machine to bring it within target

Offset Alignment

1. Mount the dial indicator on the hub OD
2. Read TIR through one revolution
3. Halve the TIR to get the offset
4. Adjust to within target

The speed bands below are the most misalignment to leave in the drive, not a target to align to. The faster the coupling runs, the less it should be asked to absorb.

Axial Gap Setting

• Measure the gap between the hub faces
• Compare it with dimension G for the coupling size (table below)
• Adjust the motor or driven machine position if needed
• Re-verify alignment after any adjustment

On SMI's FG-series full and half gear couplings, the gap G between the hub faces shown on the catalogue drawing is:

Ratings and bore sizes for each size are on the full gear coupling and half gear coupling pages. If your drawing specifies a different gap — for a spacer coupling, for example — the drawing governs.

Re-check After Tightening the Foundation Bolts

Foundation bolts pull the machine down as they are tightened and can shift the motor by 0.05–0.1 mm, enough on its own to take the drive outside the parallel target. Re-check alignment after every foundation bolt is fully tightened, not before.

Grease Fill and Sleeve Assembly

Use a coupling grease, not ordinary bearing grease. Coupling greases are classed CG-1, CG-2 or CG-3 under AGMA 9001 and resist the centrifugal separation that leaves a dry cake of thickener on the teeth. EP2 lithium-complex coupling greases are common for standard duty, but an NLGI grade on its own says nothing about separation resistance, and high speed, high ambient temperature or wet conditions change the grade. The grease guide covers grade selection.

Initial Fill

• Use the grease grade specified for the size and duty
• Fill the sleeve cavity to 30–50% of its volume; do not overfill
• Make sure grease reaches all the teeth
• Wipe excess grease from the seals

Overfilling is the most common cause of grease leakage. An overfilled sleeve churns the grease and builds pressure as it warms, which pushes the end seals out, and the grease left on the teeth dries faster. Use the quantity the coupling manufacturer states for your size — IS 12405 requires the manufacturer to state it for each coupling size.

When grease is added through the grease plugs, as it is at re-greasing, remove one plug and inject grease through the other until grease appears at the open hole, then refit the plug. Never pump grease in with both plugs fitted: the pressure can damage the end seals.

Sleeve Installation

• Slide the sleeve over one hub and engage the teeth fully before going further — never force it
• Centre the sleeve over both hubs so the gear teeth on both hubs sit fully within it
• Check that the grease seals are correctly seated at both ends
• Use no heat and no force: if the sleeve will not slide freely, check the bore and the tooth engagement

Full Gear Coupling

1. Separate the sleeve halves (if split) and engage one on each hub
2. Bring the sleeve flanges together with the gasket between them
3. Install and torque the bolts in a star pattern
4. Verify free rotation

Half Gear Coupling

1. Position the sleeve on the gear hub
2. Align the bolt holes with the rigid hub flange, with the gasket between them
3. Install and torque the bolts
4. Check for binding

Final Checks

Before Startup

• All fasteners torqued to specification — hub retention, sleeve bolts and foundation bolts
• The drive turns smoothly by hand, with no binding, clicking or resistance
• Both end seals evenly seated and not displaced during sleeve assembly
• A paint reference mark on the coupling at the shaft end, so any axial hub migration shows up during early running
• Guards installed correctly
• Grease plugs or fittings accessible
• Baseline readings recorded: alignment, gap G and bolt torques

Initial Startup

• Run without load briefly
• Monitor for noise, vibration and temperature
• Check for grease leakage
• Record readings for future reference

After Thermal Stabilization

• Re-check alignment after warm-up — thermal growth moves the shafts
• Verify temperatures are normal; a coupling running more than 20°C above ambient needs investigating (see troubleshooting below)
• Check the paint mark for any hub movement
• Record hot alignment readings
• Document all installation data

From here the coupling moves onto routine maintenance: daily visual checks, weekly temperature readings, monthly grease condition checks, periodic relubrication and an annual alignment check. The gear coupling maintenance schedule template sets those intervals out, with a record sheet for each drive.

Common Installation Mistakes

Each of these shortens gear coupling life, and each is preventable at installation.

Troubleshooting After Installation

Find the symptom, then work through the likely causes.

For the wear patterns found when a coupling is opened up, see common gear coupling failures and how to prevent them.

Contact SMI for installation support, or call our technical team on +91 63510 70577. As a gear coupling manufacturer in Ahmedabad, we machine bores and keyways to your shaft sizes in-house at our Odhav factory.

Get this checklist to your fitter

A checklist is only useful in the hands of the person doing the job. If you want this as a printable sheet for your maintenance team — one page, in the order the work is actually done, with space to record the readings taken — ask us and we will send it across with your enquiry.

We supply the couplings and we take the call when an installation goes wrong, so the checklist reflects what actually causes callbacks: soft foot never checked, alignment set cold and never re-checked hot, and bolts torqued by feel. If you want the reasoning behind each step rather than just the sequence, our technical library covers why soft foot, pipe strain and the cold offset dominate alignment outcomes in more depth than belongs on a shop-floor sheet.

What we can do alongside the coupling

• Supply the coupling machined to your measured shaft diameters and keyways, so the fit is right before anyone starts aligning.
• Confirm the shaft gap and any axial float your machine needs, from the drawing or your measurements.
• Advise the correct grease and initial fill for the size and duty.
• Talk your fitter through the sequence on the phone if the installation is unusual.

Frequently asked questions

How accurately does a gear coupling need to be aligned?

As accurately as you practically can, regardless of the coupling's rated capability. SMI's recommended targets at assembly are 0.10 mm TIR on the hub face (angular) and 0.05 mm TIR on the hub rim (parallel), measured with a dial indicator. SMI flexible gear couplings accommodate up to ±1.5° of angular misalignment per gear mesh, but that rating is there for residual error and thermal growth — every fraction you leave behind is sliding tooth contact and heat for the life of the drive.

What is soft foot and why does it matter?

Soft foot is when one machine foot does not sit flat on its base, so tightening the bolt distorts the housing and pulls the shaft out of line. It defeats alignment done afterwards. Check and shim all feet before you touch the alignment readings.

What should I check after the first few hours of running?

Bolt tightness, coupling temperature by hand or with an infrared thermometer, any grease leakage at the seals, the paint mark on the hub for axial movement, and vibration by feel or meter. Then re-check alignment once the machine has reached operating temperature, because thermal growth moves the shafts.

Why is my gear coupling leaking grease?

Overfilling is the most common cause: a sleeve packed beyond its specified quantity churns the grease and builds pressure as it warms, which displaces the end seals. Other causes are seals displaced during assembly, operating misalignment beyond what the seals tolerate, or the wrong grease grade. Check the fill quantity first, then re-seat the seals before re-greasing.

What grease should go into a gear coupling at installation?

A coupling grease, not ordinary bearing grease. Coupling greases are classed CG-1, CG-2 or CG-3 under AGMA 9001 and resist the centrifugal separation that leaves a dry cake of thickener on the teeth. EP2 lithium-complex coupling greases are common for standard duty; high speed, high ambient temperature or wet conditions change the grade, so confirm it for the coupling size and duty before filling.

Can a gear coupling hub be hammered onto the shaft?

No. A hammer blow on the hub face sends a shock through the gear teeth that can crack tooth tips or start micro-fractures. Press the hub on with a hydraulic press or hub fitting tool for a clearance fit, or heat it evenly in an oven or induction heater for an interference fit — never with an open flame on the bore.

Super Mech Industries — Odhav, Ahmedabad, Gujarat 382415, India. Phone: +91 63510 70577. Email: smigvs@gmail.com. ISO 9001:2015 certified.