Quick summary: the serpentine belt transfers engine power from the crankshaft to accessories (alternator, A/C, power steering, water pump or fan) via a single continuous rubber belt. It must be routed correctly and held at the correct tension by a spring-loaded tensioner (or an adjustable bracket/tensioner). Replace the belt if it’s cracked, glazed, shredded, or slipping. Below is a clear, step-by-step beginner-level procedure specific to a Nissan Navara D21 (1990s/’97 generation) layout — plus full descriptions of every component, how the system works, what can go wrong, and safety notes.

Important safety first
- Work on a cool engine with the ignition OFF and the key removed. Never work near a running engine.
- Set parking brake, chock wheels.
- Disconnect the negative battery cable if you will be moving electrical components or if there’s any risk of starting the engine while your hands are inside the engine bay.
- Wear safety glasses and gloves. Keep fingers clear of pulleys and springs when tension is released.
- Use jack stands if you must raise the vehicle. Don’t rely on a jack alone.

Key components — names, what they look like, and what they do
- Serpentine belt (drive belt): a continuous rubber belt with ribs on the underside that grips pulley grooves. It’s the “drive link” carrying power from the crank pulley to accessories.
- Crankshaft pulley (harmonic balancer): largest pulley on the bottom center of the engine. It’s the belt’s drive source — imagine the pedal axle of a bicycle that makes the whole system move.
- Alternator pulley: smaller pulley on the alternator. Spins the alternator to produce electrical charging.
- Power steering pump pulley: drives the hydraulic pump for power steering; if this stops the steering gets heavy.
- A/C compressor pulley: on the air-conditioning compressor. If it’s not driven, A/C stops cooling.
- Water pump pulley (if belt-driven on your engine): drives coolant circulation through the engine.
- Idler pulleys: smooth pulleys used only to route the belt correctly, keep belt contact on other pulleys, and help align the belt.
- Tensioner pulley (spring-loaded): a pulley on a spring-loaded arm that keeps the belt tight. For many D21s it’s a built-in ratcheting spring tensioner that you rotate to relieve tension. Analogy: the tensioner is like a hand continually pulling on a rubber band to keep it taut.
- Mounting/bracket bolts: hold accessories and tensioner in place. Some systems use an adjustable alternator bracket vs. an automatic tensioner.

Theory — how the system works
- The crank turns, the belt wraps around accessory pulleys. Friction between the belt ribs and pulley grooves transfers rotational force. The belt must have correct alignment and tension so it doesn’t slip, squeal, or jump off pulleys.
- The tensioner provides a preset tension via its spring and sometimes a damping mechanism. Too loose and the belt slips; too tight and bearings in accessories wear prematurely.
- Idlers and pulley alignment direct the belt path and maintain appropriate contact (wrap) on driven pulleys for torque transmission.

Why this repair is needed
- Belts age: rubber dries, cracks, loses ribs, curls, or glazes. A failed belt can stop the alternator, power steering, A/C and possibly the water pump — causing overheating and loss of electrical charging, which can strand you or damage the engine.
- Replacing the belt proactively is inexpensive relative to the cost and safety risk of a broken belt.

Signs a belt or parts need replacement
- Visible cracks across the ribs, missing rib material, fraying on the edges, or shiny glazed surface.
- Squealing noise on startup or under load — suggests glazing, contamination, or misalignment.
- Belt “feathering” or chunks missing, severe wear, or slipping.
- Excessive wobbly pulley movement (bearing wear).
- Engine overheating or battery not charging (possible belt drive failure).
- If the tensioner is noisy, doesn’t hold tension, or is leaking grease, replace it.

Tools and parts you’ll need
- New correct serpentine belt (match OEM part number or correct size and rib count — get the belt specifically for your 1997 D21 engine).
- Possibly new tensioner and/or idler pulleys if they’re noisy or have play.
- Basic hand tools: socket set (metric), ratchet, breaker bar or long-handled wrench (to operate tensioner), combination wrenches, screwdriver, pliers.
- Serpentine belt tool or long 15–18 mm wrench/ratchet (fits tensioner bolt); a 3/8” or 1/2” drive depending on tensioner.
- Torque wrench (for re-tightening any bolts to spec).
- Pen and paper or camera (to copy routing diagram if no sticker present).
- Flashlight, penetrating oil (for stuck bolts), gloves, safety glasses.

Before you start — routing diagram
- Find the belt routing sticker under the hood (often on the radiator support or fan shroud). If it’s missing, take a photo or draw the routing before removing the old belt. DO NOT rely on guessing.
- The belt wraps around each pulley; pay attention to which pulleys have the belt going over vs under. A wrong routing can make accessories spin the wrong way or not be driven.

Step-by-step replacement procedure (beginner-friendly)
1) Preparation
- Park on level ground, engine cool, key out, parking brake on, wheels chocked.
- Disconnect negative battery cable (optional but recommended).
- Locate belt routing diagram; sketch or photograph if needed.

2) Gain access
- Remove any engine covers, splash shield, or the battery if it obstructs access to the belt path or tensioner. On some D21s you may need to remove air intake pieces or the upper engine cover for working space.

3) Identify the tensioner type and location
- Locate the spring-loaded tensioner (usually a pulley on a pivot arm). It will have a square hole or bolt head for your ratchet/breaker bar.
- Note the direction you must pull to relieve tension — there is often an arrow or the spring arm position helps you see which way to move it.

4) Relieve tension and remove the old belt
- Place your ratchet/breaker bar or serpentine tool on the tensioner. Apply steady force to rotate the tensioner and reduce belt tension.
- While holding the tensioner rotated, slide the belt off one accessible pulley (usually the easiest is the alternator or idler).
- Slowly release the tensioner back to position. Remove the belt completely.
- If the tensioner is a manual adjuster (older style), loosen the lock and slide the adjuster to reduce tension and remove belt.

5) Inspect components thoroughly
- Check each pulley for lateral play or rough bearing feel. Spin each pulley by hand (with the belt off) — bearings should be smooth and quiet with no roughness or grinding.
- Inspect pulley surfaces for damage, rust build-up, or misalignment.
- Check the tensioner for smooth motion and any signs of oil or damage. If tensioner is noisy, shows weak spring movement, or the arm is loose, replace it.
- Check accessories (alternator, power steering pump, A/C compressor) for free rotation and no grinding.

6) Compare old vs new belts
- Place the old and new belts side-by-side: ribs count should match, same length, and new belt should not be stretched or cracked.

7) Route the new belt
- Following the routing diagram, start routing the belt around the pulleys leaving one pulley (usually the easiest to reach) for last — typically the tensioner or an idler.
- Make sure the ribs seat correctly into the grooves of each pulley as you route it.

8) Re-tension the belt
- Rotate the tensioner again to give slack and slip the belt over the final pulley. Slowly release the tensioner so it applies tension to the new belt.
- Visually check the belt sits centered in the pulleys and ribs are fully seated. Check alignment by sight—belt should run straight across pulley faces, not be cocked.

9) Check tension
- Factory tensioners are automatic; just verify belt deflection by pressing mid-span (manual-rule: about 1/2"–1" deflection on most systems — but check factory spec). If you replaced a manual tensioner, set to factory tension and tighten the lock bolt to spec.
- If you have a belt tension gauge, use it to set the correct tension per factory manual.

10) Final checks
- Double-check routing, that all bolts removed are re-installed and torqued to spec (consult factory manual).
- Reconnect battery if disconnected.
- Start engine and observe: belt should run smoothly without squeal or wobble. Check for unusual noises. Turn A/C on, turn steering wheel, watch for any issues.
- After a short test drive, recheck belt tension and pulleys for tightness.

What can go wrong (and how to avoid it)
- Incorrect routing — consequences: accessory not driven, reversed wrap leading to slip, overheating, alternator not charging. Avoid by copying the routing diagram before removing the old belt.
- Wrong belt size — can be too long (slack) or too short (won’t fit). Use exact OEM or correct replacement by engine code.
- Not replacing a failing tensioner/idler — a new belt on old bad pulleys/tensioner will fail sooner. If pulleys have play or noise, replace them with the belt.
- Overtightening (on manual tensioners) — too much tension shortens bearing life and can damage accessories. Use factory tension specs.
- Pinched fingers or tool slippage when releasing tensioner — keep hands clear of the tensioner arm’s travel path; hold tool firmly and release slowly.
- Starter cable/ battery left connected and accidental engine start — disconnect negative battery if risk exists.
- Sheared or damaged tensioner bolt — use good tools, correct socket size, and steady force.

Troubleshooting after installation
- Squeal on cold start: belt glazing or minor misalignment. Check pulleys and belt seating.
- Squeal under load: too loose or contaminated belt (oil/grease). Check tension and cleanliness of pulleys/belt.
- Belt jumps off: misaligned pulleys or wrong routing or worn pulleys. Inspect pulley faces and alignment.
- Battery not charging: belt not on alternator pulley correctly or slipping — inspect routing and tension.

Replacement extras and maintenance tips
- Replace the tensioner and idlers if mileage/age is high (common practice — they’re inexpensive insurance).
- Clean pulleys with a rag; do not use harsh solvents on the new belt. Keep engine oil or coolant off pulleys and belt — contamination causes slippage and rapid deterioration.
- After 1–2 days of driving, recheck belt tension and pulley bolts.
- Keep the OEM part numbers handy for future replacement: belts and tensioners vary with engine (KA24, Z24, diesel etc.). If possible, bring vehicle details to parts store for correct match.

Time estimate and common costs
- Time for an experienced DIYer: 30–90 minutes. For a beginner allow 1.5–3 hours.
- Parts: serpentine belt typically inexpensive (– depending on brand); tensioner/idler assembly more (–0). Labor cost at a shop varies accordingly.

Final checklist before finishing
- Correct belt routing verified.
- Pulleys and tensioner inspected and replaced if needed.
- Proper tension applied.
- No unusual noises when engine runs.
- All removed components reinstalled and battery reconnected.

That’s the full procedure and background in straightforward steps. Follow it carefully, move deliberately, and replace tensioner/idlers if in doubt — they’re the usual weak links.
rteeqp73

1986-1997 Nissan D21 Hardbody (King Cab - 2WD) FMVSS 301 Rear Crash Test A 50 Mph (80 Km/h), 70% overlap rear crash test. The barrier weighs 1360 kg. (About 3000 lbs.) Part of a series to test this current ...

Nissan Navara D21 Radiator Replacement A hot Aussie summer looming and a dodgy old radiator were not going to play nice together.

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