1) Theory — what the tensioner pulley does and why it fails
- Purpose: the tensioner/idler pulley gives correct belt tension and wrap angle so the crankshaft can drive the fan, water pump and generator/dynamo without slip. It also keeps belt alignment and takes up slack.
- Failure modes: pulley bearing wear (noise, rough rotation, radial/play), pulley face wear or groove mis-shape, seized pivot, or misalignment. These cause belt slip (loss of drive of fan/charging), vibration, heat, accelerated belt wear, and poor charging/overheating.
- Mechanics: a worn bearing increases radial runout and friction so the belt rides off-center and slips under load. Insufficient tension reduces friction force between belt and pulley causing slip; excessive tension overloads bearings and shafts.

2) Symptoms that point to the tensioner pulley
- Squeal from front of engine on startup or under load.
- Belt tracking off pulley edges or obvious wobble.
- Visible play if you try to rock the pulley by hand.
- Poor charging (weak/dying battery), overheating fan not running effectively, or rapid belt wear.

3) Tools & safety (short)
- Tools: spanners/sockets for pulley pivot and retaining nut, screwdrivers, breaker bar, torque wrench, new pulley (or bearing), straightedge or ruler, belt tension gauge or rule for deflection measurement, replacement belt if needed.
- Safety: engine off, key out, battery negative disconnected, tractor immobilised, cooling fan stationary.

4) Ordered repair procedure with theory at each step
1. Inspect visually and by hand
- Theory: confirm symptom source before replacing parts. Look for oil/grease on belt, glazing, missing belt ribs, pulleys with nicks.
2. Disconnect battery negative
- Safety: prevents accidental starters and shorts.
3. Ease or remove belt
- Procedure: loosen generator pivot / accessory adjuster so belt can be removed. If a dedicated idler/tensioner holds tension with a bolt, loosen that to relieve belt.
- Theory: remove load from pulley so you can spin and inspect it freely and replace parts safely.
4. Check pulley running and play
- Procedure: spin the pulley by hand and feel for roughness or noise; check radial and axial play by rocking it.
- Theory: a smooth free spin with no play means bearing is okay; rough/loose means bearing failure and the pulley will let the belt slip and misalign.
5. Check alignment and shaft/spacing
- Procedure: place a straightedge across the crank pulley, tensioner and driven pulleys; all faces should be coplanar. Check for worn spacers or bent brackets.
- Theory: misalignment causes edge wear and reduces effective belt wrap, increasing chance of slip.
6. Remove pulley (if replacement/repair needed)
- Procedure: unbolt retaining nut/bolt, note any shims/spacers orientation and remove pulley. If the pulley has a pressed-in bearing you may replace the whole pulley; if serviceable, remove bearing using a press or correct tools.
- Theory: removing the faulty bearing/pulley eliminates the rough surface and play causing slip and noise.
7. Fit replacement pulley or new bearing and reassemble
- Procedure: press-fit new bearing or fit new pulley, reinstall spacers/shims exactly as removed, torque retaining fastener to spec (use manufacturer spec or snug plus small angle; if unknown, firm but avoid overstressing threads). Ensure pulley face is parallel to other pulleys.
- Theory: a correctly fitted pulley restores concentric rotation and correct lateral position so belt contacts properly.
8. Reinstall belt and set initial tension
- Procedure: position belt and move generator/idler to take up slack. For preliminary tension, tighten pivot bolts hand-tight so position is set.
- Theory: correct tension is needed for frictional drive. Too loose = slip; too tight = bearing/shaft overload.
9. Measure and set final belt tension (use deflection rule)
- Rule-of-thumb: deflection of roughly 1/64" per inch of span between pulleys (about 0.4 mm per 10 mm) under moderate finger/thumb pressure, or 8–10 mm (5/16"–3/8") for a typical 18–24" span. If you have a belt-tension gauge use recommended spec for V-belt.
- Procedure: apply moderate force mid-span and adjust generator/idler until deflection is correct, then tighten mounting/pivot bolts to lock position. Re-check deflection after tightening.
- Theory: this gives correct belt tension so friction transmits torque without overstressing bearings.
10. Re-check alignment and rotation
- Procedure: spin the pulley by hand (or start engine briefly) and observe tracking, listen for noise, check for wobble. Re-tension if belt seats differently after a run-in.
- Theory: a new bearing/pulley will seat and may slightly change tension; verifying ensures no residual slip.
11. Test under load
- Procedure: start engine, observe charging (dynamo/generator voltage), fan operation, and any noise. Rev engine and watch belt slip or tracking.
- Theory: confirms that the pulley/belt system now reliably transmits power to cooling and charging systems.

5) How the repair fixes the fault (concise)
- Replacing a worn/bad tensioner pulley removes bearing play and roughness. That restores concentric rotation, corrects pulley surface profile, and allows correct belt seating. Re-aligning and setting correct tension restores proper frictional contact and wrap, preventing slip. The net result: no squeal, correct driving of fan/water pump/generator, better charging, less belt wear, and reduced load on shafts and bearings.

6) Quick aftercare and checks
- Re-check tension and alignment after initial few hours of operation and again after 50–100 miles/tractor-hours.
- Replace belt if glazed or cracked — a new pulley on an old belt will still slip.
- Keep pulley mounting hardware tight and check for oil/grease contamination (replace seals/gaskets if contaminated).

End.
rteeqp73

How to Replace the Rear Axle Seal and Bearing on a Ferguson TE20 Tractor In this video I go through fitting the rear axle seal and bearing on our 1948 TEA20 tractor. The parts used in this video can be ...

Ferguson Tractor TE20 Horn and Dash Restoration https://www.facebook.com/DR-Tractors-1555160931445665/?fref=ts.

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