Overview / theory (short)
- The belt transmits engine crankshaft torque to accessory components (water pump, cooling fan, alternator/stator/charging, sometimes power take-off). It must have correct routing, tension, and pulley alignment to deliver torque without slipping or causing excess bearing load.
- Failure modes: cracking, glazing, missing ribs (if multi-rib), contamination (oil/antifreeze), stretched/creeped belt, or worn/damaged pulleys/tensioner. Faults produce squeal, poor charging, overheating, or sudden loss of driven component.
- Replacing the belt restores frictional drive, corrects slip, and eliminates vibration/noise if pulleys/tensioners are ok. If pulleys/tensioners are bad, a new belt will fail prematurely — you must inspect/replace them as needed.

Step‑by‑step procedure in order, with why for each step
1. Safety and preparation
- Kill engine, remove key, chock wheels, set parking brake. Let engine cool. Disconnect negative battery terminal (prevents accidental cranking, shorts when moving alternator or loosening bolts).
- Why: prevents injury and electrical shorts.

2. Gather tools and parts
- Tools: correct wrenches/sockets for alternator/idler/adjuster bolts, pry bar or long lever for tensioning, torque wrench if you have spec, belt tension gauge or ruler for deflection measurement, rag, flash/inspection light.
- Parts: correct replacement belt (match OEM length/profile or conversion kit if using serpentine retrofit), inspect and be ready to replace idler/tensioner/alternator pivot hardware if worn.
- Why: correct belt and tools avoid wrong fit and damage.

3. Inspect system before removal
- Visually inspect belt condition, pulley grooves, bearings (spin pulleys by hand for roughness/play), look for oil/grease on pulleys, check alignment of pulleys (visual line).
- Why: confirms whether belt alone is the problem or other components must be serviced. Replacing belt without fixing a bad bearing or misaligned pulley wastes effort and yields repeat failure.

4. Note and/or mark belt routing
- Draw or photograph the belt route. If it's a serpentine/ribbed belt, note rib orientation.
- Why: correct routing is essential for correct direction of wrap and tension on each accessory.

5. Relieve tension and remove old belt
- Locate the belt tensioner or the adjustable component (common on MF135/150/165 the alternator/tensioner is adjustable rather than a spring tensioner; retrofit kits may have an idler). Loosen the adjuster/alternator pivot enough to relieve tension; use a lever on the adjuster arm or rotate tensioner if spring-loaded.
- Remove belt from smallest/difficult pulley first, then work it off.
- Why: controlled release prevents sudden movement and allows safe removal.

6. Inspect pulleys and accessories again, correct issues
- Spin water pump pulley, alternator pulley and any idler: listen for grinding, check lateral play. Check pulley faces for scoring, buildup, or missing/flattened ribs. Check bearings and fan hub.
- Check pivot/adjuster bolts and alignment shims.
- If bearings are noisy, pulleys glazed, or alignment off, repair/replace those parts now.
- Why: a new belt will fail quickly if pulleys or bearings are bad or misaligned.

7. Fit the new belt dry to check routing and length
- Route the new belt over pulleys except leave it off the last pulley so you can tension easily.
- Ensure ribs seat correctly in grooves (if ribbed serpentine).
- Why: verifies belt length and that routing matches pulleys; prevents trying to force an incorrect belt.

8. Apply tension and set adjustment
- For adjustable alternator tension: move alternator/idler outward to apply tension, then tighten the pivot/lock bolt and the adjuster bolt incrementally while maintaining proper tension.
- For spring tensioners: release tensioner to apply correct tension automatically.
- Tension guideline: for older tractors without a published spec, a typical single-rib belt deflection is about 1/4"–3/8" (6–10 mm) at midspan with moderate thumb pressure; for multi-rib serpentine belts the manufacturer’s spec or a belt tension gauge is preferred. Do not over‑tighten — that overloads bearings.
- Why: correct tension prevents slip (if too loose) and avoids bearing/damage (if too tight). Proper tension ensures intended frictional torque transfer.

9. Check alignment and pulley seating
- Ensure belt runs square on each pulley; pulleys should be coplanar. If necessary loosen and realign alternator/idler, or add/remove shims.
- Why: misalignment causes edge wear, rapid belt loss and noise.

10. Tighten final bolts to proper torque
- Tighten pivot/adjust bolts securely. If you don’t have torque specs, tighten snugly then back off slightly and recheck alignment/tension after running.
- Why: secure fasteners keep adjustment stable.

11. Run engine and observe
- Reconnect battery negative, start engine, observe belt at idle and a little above idle: look for wobble, noise, sway of alternator, and check accessories work (fan spins smoothly, charging system produces expected voltage).
- After a few minutes, stop engine and recheck tension and retighten adjuster bolts if they moved.
- Why: belts seat and can stretch a little on first run — recheck prevents early failure.

12. Final checks and break‑in
- Re-inspect after 24–48 hours operation (or first few hours), remeasure deflection, check for oil contamination and retorque bolts.
- Dispose of old belt properly.
- Why: ensures reliability after initial stretch and seating.

How this repair fixes the fault (mechanical theory)
- Frictional drive: The belt transmits rotational torque through friction with pulley surfaces. A worn/brittle/glazed or contaminated belt cannot generate sufficient friction, so it slips under load. Replacing with a proper, undamaged belt restores the designed friction coefficient and contact geometry (ribs seated in grooves), eliminating slip and associated symptoms (squeal, slow fan, undercharging).
- Proper tension: Correct tension provides sufficient normal force between belt and pulley, increasing frictional capacity. A loose belt reduces transmitted torque; over‑tightening increases bearing loads and shortens belt life. Setting correct tension restores torque transmission while protecting bearings.
- Pulley condition and alignment: If pulleys or bearing play are fixed during the replacement, the belt runs true and wears evenly. Removing a contaminated/crumbled belt and replacing it reduces vibration and prevents foreign material from damaging pulleys.
- Overall result: replacement restores horsepower transfer to cooling and charging systems, preventing overheating, restoring charging voltage, stopping noise and preventing abrupt failure that could strand the tractor.

Common symptoms that indicate belt replacement will fix the problem
- High‑pitched squeal on startup or under load (belt slip).
- Visible cracking, missing ribs, glazing or frayed edges.
- Overheating or low coolant flow due to fan/water‑pump slip.
- Low charging voltage while alternator appears intact.
- Slippage under load (e.g., belt jumps or chirps when engaging PTO).

Common mistakes to avoid
- Replacing belt but not addressing bad bearings, idler or misalignment.
- Over‑tightening belt and destroying bearings.
- Using wrong‑profile/short belt or reinstalling with reversed rib orientation.
- Not retorquing/rechecking after initial run.

Quick note on MF135/150/165 specifics
- These tractors originally used V‑belt arrangements with adjustable alternator tension; some owners retrofit multi‑rib (serpentine) kits. The same theory applies: ensure correct belt profile/length and use the correct tensioning method for whatever system is fitted. If you have the original V‑belt, match replace with correct V‑section belt.

Done.
rteeqp73

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