Tools & PPE
- Safety: safety glasses, heavy gloves, steel-toe boots, hearing protection, dust mask if dusty.
- Tools: metric/imperial socket & wrench set, torque wrench, breaker bar, ratchet, combination screwdrivers, snap-ring pliers, pry bar, hammer, punch, rubber mallet, circlip pliers, bearing puller, drift/soft-faced hammer, needle files or emery cloth, shop rags, degreaser.
- Specialty: belt-tension gauge (or deflection gauge), dial caliper, straight edge/feeler gauge, torque screwdriver (small fasteners), pry-bar for tensioner, impact (optional), anti-seize, Loctite (medium strength), grease.
- Lifting/support: tractor jack or lift, blocks/chocks, jack stands.
- Consumables/parts: new timing belt (correct OEM or spec replacement), tensioner/idler pulleys (recommended), bearings/seals if worn, replacement fasteners/lock-washers, light grease.

Safety precautions (do these first)
1. Park baler on level ground; chock wheels. Lower any hydraulics and relieve pressure.
2. Shut off tractor, remove key, disconnect battery on tractor if needed. Remove PTO shaft from baler and cap both ends to keep clean.
3. Ensure no stored energy in springs; consult manual to safely relieve any spring tension on knotters or pick-up.
4. Wear PPE; keep hands and clothing clear of rotating parts when testing.

Preparation
1. Obtain MF20 service/parts manual and compare belt length/profile to replacement. Use OEM part or exact spec (tooth profile, pitch, width).
2. Clean working area and remove crop residue around drive area so you can see timing marks and fasteners.
3. Photograph routing of belt and note all alignment/timing marks on pulleys and housings. Mark pulleys with paint or scribe so you can reinstall with identical orientation.

Step-by-step replacement
1. Remove guards and covers
- Remove all belt guards, access plates, and any components blocking the belt/tensioner. Keep fasteners grouped and labeled.

2. Relieve belt tension
- Locate the tensioner or idler assembly.
- If spring-loaded, use appropriate tool (pry bar or socket on tensioner bolt) to rotate tensioner and relieve tension; secure tensioner in the released position if needed.
- If adjustable, loosen the adjuster bolts until belt is loose.

3. Mark timing positions
- If there are timing marks on pulleys/shafts, mark their relative positions on both pulley and housing to preserve timing. Take photos from multiple angles.

4. Remove the old belt
- Slip the belt off the smallest pulley first, then off the rest. Inspect belt teeth and backing for damage; note any contamination or damage patterns that indicate a problem (bearing wear, rubbing).

5. Inspect components
- Spin each pulley/idler by hand. Check for rough bearings, play, or noise. Check shafts for scoring, keyways for damage.
- Inspect belt guides, tensioner arm, and bracket for cracks or wear.
- Replace any pulley or bearing that doesn't spin freely or has axial/play movement.
- Check pulley alignment with a straight edge; correct misalignment before fitting new belt.

6. Replace pulleys/tensioner/bearings as required
- Use bearing puller or drift to remove worn bearings. Press or install new bearings per service manual. Clean bores and use light grease only where specified. Use anti-seize on shafts if recommended.
- Install new tensioner/idler pulleys—ensure bushings/bolts are torqued to spec and use new washers/lock nuts or Loctite as required.

7. Fit the new belt
- Compare new belt to old (length, tooth profile).
- Route belt according to marks/photos. Place belt on largest pulley first or as required by clearance, then onto smaller pulleys; ensure teeth fully seat in sprockets.
- Verify belt direction if directional marking exists; install per marking.

8. Set belt tension
- Use recommended method in service manual. If manual gives deflection: place a ruler across span, push mid-span to measure deflection. Common approach for synchronous/timing belts: use a belt tension gauge or set deflection to manufacturer spec (do NOT over-tighten).
- If no spec available, set to firm with minimal sag — the belt should not be loose and should allow about 1–3 mm of finger pressure deflection on short spans; more accurate: use a tension gauge to reach correct tension frequency. Over-tightening will cause premature bearing/shaft failure.
- Tighten the tensioner/adjuster bolts gradually while maintaining tension and alignment. Torque bolts to spec (use manual value; if unknown, snug then check).

9. Seat the belt
- Rotate the system slowly by hand (or slowly with tractor PTO disconnected and baler driven by hand tools) for 3–5 revolutions to seat the belt. Re-check tension and alignment; adjust if tension has relaxed.

10. Final torque & safety check
- Torque all fasteners and pulleys per specs. Apply Loctite where recommended.
- Ensure guards and covers are reinstalled and secure.

11. Test run
- Reattach PTO, start tractor at low engine speed, engage baler slowly. Listen for unusual noises, watch pulleys for wobble, belt tracking, heat, or smoke.
- Run at operating speed for a short time, then shut down and re-check belt tension and fasteners. Recheck again after the first few hours of operation.

How each tool is used (short)
- Torque wrench: tighten pulley/tensioner bolts to correct torque to prevent loosening or over‑stress.
- Belt-tension gauge/deflection gauge: set correct belt tension—measure mid-span deflection or frequency.
- Bearing puller/press: remove/install pulleys or bearings without damaging shafts.
- Pry bar/socket on tensioner: release or adjust tensioner arm safely.
- Straight edge/feeler gauge: check pulley alignment; misalignment causes belt wear.
- Caliper: verify pulley diameters and key dimensions against new belt spec.
- Impact (optional): remove stubborn fasteners quickly—follow with torque wrench for final torque.

Replacement parts to have on hand
- New timing belt (OEM or exact spec)
- Tensioner pulley (new) and spring assembly if present
- Idler pulleys (1–2) and associated bearings
- Bearings/seals for pulley shafts
- Fasteners, lock washers, Loctite
- PTO shaft protectors/caps if damaged
- Guards/cover replacements if cracked

Common pitfalls & how to avoid them
- Working with PTO connected: always disconnect and cap drive shaft.
- Not marking timing/pulley positions: leads to incorrect timing — mark and photograph.
- Reusing old belt or worn idlers: reduces life; replace idlers/tensioner with belt.
- Incorrect tension: too loose = slippage/noise; too tight = bearing/shaft failure. Use gauge/manual spec.
- Misalignment: causes premature tooth wear and cracking; check straight edge alignment before tensioning.
- Over-torquing small fasteners: strip threads or break studs—use correct torque.
- Forgetting guards: always reinstall guards before testing.
- Ignoring bearing play: noisy bearings ruin new belts quickly—replace rough bearings.

Post-replacement checks
- After 10–30 minutes of operation, re-check belt tension, pulley bolts, and alignment.
- Inspect belt for even wear and proper seating after first few bales; re-tension if necessary.

Final note
- Always follow the MF20 service manual for model-specific torque values, tension specs, timing marks, and safe spring/energy release procedures. Replace the belt with the correct OEM or equivalent specification for tooth pitch, width and length.
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MF 20 Baler & MF 575 tractor Tim Poulter's Old Massey baler and tractor in action August 2021 in Great Raveley, being driven by Alec Glover.

Massey Ferguson Balers and Hay Tools 1980

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