Short, clear guide to the serpentine belt tensioner/pulley on a Jeep Grand Cherokee (WH/WK). Written for a beginner mechanic — describes every component, theory, how to diagnose failures, and step‑by‑step replacement/inspection procedure. No extra chatter.

What the part is and why it matters
- Purpose: The tensioner keeps the serpentine belt at the correct tension so the crankshaft can reliably turn accessory pulleys (alternator, A/C compressor, power steering pump, water pump on some engines, idlers). If tension is wrong the belt slips, squeals, wears fast, or breaks — causing loss of charging, A/C, power steering and possibly engine overheating.
- Analogy: Think of the belt as a bicycle chain and the tensioner as the derailleur spring that keeps the chain tight. If the spring fails or the pulley bearing seizes, the chain (belt) can fall off or skip teeth and you lose drive to accessories.

Main components (every part you will see/function)
1. Serpentine belt
- Flat ribbed belt that snakes around accessory pulleys. Transfers rotational power from crankshaft pulley to accessories.
- Signs of wear: cracks on ribs, glazing (shiny), missing pieces, frayed edges.

2. Tensioner assembly (spring‑loaded)
- Mounting bracket/pivot housing: bolts to the engine block/cover.
- Tensioner arm (lever): the pivoting arm that pushes the pulley against the belt.
- Internal spring (and usually a damper): provides tension force and reduces oscillation/vibration.
- Pulley (on the arm): small round wheel that contacts the belt. Contains a bearing.
- Pivot bolt: secures tensioner to the engine; often the largest bolt in the assembly.
- Square or hex working point: a square hole or hex where you attach a breaker bar or serpentine tool to relieve tension.

3. Idler pulleys (nearby)
- Fixed pulleys used to route and support the belt. Also have bearings that can wear.

4. Accessory pulleys
- Alternator, A/C, power steering, crankshaft, water pump. Misalignment or bearing failure here affects belt life.

5. Fasteners, spacers, shims, washers
- Small parts that hold pulleys/tensioner in place. Keep track when disassembling.

Tools and consumables you’ll need
- Safety: gloves, eye protection, wheel chocks.
- Basic tools: socket/ratchet set, breaker bar or serpentine belt tool (long-handled), torque wrench, combination wrenches, screwdrivers, pry bar (small).
- Socket sizes: bring a 10–19 mm set and inch equivalents; exact size varies by engine variant.
- Replacement parts: new tensioner assembly or replacement pulley (many tensioners replace as a unit), new serpentine belt (recommended), possibly idler pulleys.
- Pen & phone/camera: to document belt routing.
- Manufacturer service manual or belt routing diagram (under hood or thermal label).

Safety first
- Park on level ground, parking brake on, engine cold.
- Chock wheels.
- Disconnect negative battery terminal if you’ll be removing electrical connectors or doing extended work (optional for pure belt work but recommended for safety).
- Support vehicle with jack stands if you need to go under it. NEVER rely on a jack alone.

Theory — how it works (brief)
- Crank pulley turns; belt transfers motion to accessory pulleys.
- Spring in the tensioner applies a steady force through the tensioner arm to keep belt tight as load and belt stretch change.
- Damper inside the tensioner reduces belt vibration and dampens shock loads (engine load changes).
- Bearing in the pulley allows smooth rotation; if bearing binds, the pulley can wobble or lock up and quickly destroy the belt.

Symptoms that tell you the tensioner/pulley is failing
- Squealing or chirping from front of engine at startup or under load.
- Belt visible glazing, fraying, or chunks missing.
- Looseness or slack in belt; belt slips off a pulley.
- Rattling or knocking noise — often a bad bearing or broken spring.
- Warning lights: battery/charging light (due to alternator not being driven).
- Poor A/C performance or intermittent power steering assist.
- Visual wobble of pulley while engine idling (use a mirror or by hand with belt removed).

What can go wrong (failure modes)
- Pulley bearing wear: roughness, noise, radial play, eventual seizure.
- Tensioner spring fatigue or break: insufficient tension, belt slip.
- Arm/pivot wear: excess play, misalignment.
- Pulley misalignment (bent arm or wrong spacer): belt tracks off.
- Corrosion or broken fasteners.
- Contamination (oil/coolant) on belt/pulley causing slippage.
- Idler or accessory pulley failure contributing to belt failure.

Inspection tests (before removing)
- With engine off and belt on: inspect belt condition, check for visible pulley wobble.
- With belt removed: spin pulleys by hand — they should spin freely and silently; no roughness, no grinding, no play. Wiggle pulleys radially — no side-to-side play.
- Check tensioner arm: with a pry bar or ratchet on the tensioner square, rotate to relieve tension and observe spring response — smooth and strong; not sluggish or sticking.

Step-by-step replacement procedure (typical)
1) Preparation
- Park, chock wheels, disconnect negative battery if desired.
- Let engine cool.
- Remove any engine covers, air intake duct, or splash shields blocking access to the belt/tensioner. On WH/WK you often need to remove the plastic engine cover by unclipping or unscrewing a couple bolts. Some models may require removing the airbox or splash guard.

2) Document belt routing
- Find sticker under hood or use a phone picture/sketch of belt routing. This is critical.

3) Relieve belt tension and remove belt
- Locate the tensioner. Identify the square head or bolt for rotating the tensioner arm.
- Use a long breaker bar or serpentine tool, place it onto the tensioner work point and rotate the tensioner in the direction that relieves tension (usually clockwise on Jeep tensioners — watch the belt side to confirm). Hold the tensioner in the released position, slip the belt off one easily accessible pulley (often the alternator), then slowly release tension.
- Remove the belt fully.

4) Remove the tensioner/pulley
- Support the tensioner arm with one hand as you remove the pivot bolt(s). Loosen the pivot bolt and remove it; some designs have one pivot bolt, others two. Keep track of shims/washers.
- Remove the tensioner assembly. If you are only replacing the pulley and the pulley is serviceable separately, remove pulley bolt and change pulley — often replacement as whole assembly is simpler and recommended.

5) Inspect surrounding components
- Spin other idler and accessory pulleys; inspect for oil leaks or coolant contamination; inspect belt path for damage or misalignment; check bracket for cracks.

6) Install new tensioner/pulley
- Fit new tensioner assembly to mounting point. Ensure any locating dowels/shims are correct and align.
- Start the pivot bolt threads by hand to avoid cross-threading.
- Torque the pivot bolt(s) to the manufacturer spec. If you don’t have the spec, snug properly and later consult factory manual to confirm final torque. (Do not under-tighten — loose pivot can shift under load; do not over-torque to the point of stripping threads.)
- If replacing pulley only, ensure pulley direction and spacer orientation match original, and torque pulley bolt to spec.

7) Refit the belt
- Route the belt according to diagram. Leave the belt off one accessible pulley (again usually alternator).
- Rotate the tensioner with the breaker bar/serpentine tool to allow the belt to be slipped into place over the last pulley.
- Carefully release tensioner so it applies tension to the belt. Ensure the belt seats in the ribs on every pulley.

8) Check and double-check
- Verify belt is fully seated in all pulley grooves and aligned.
- Reinstall any removed components (airbox, covers).
- Reconnect battery, if disconnected.

9) Start engine and observe
- Start engine and watch belt operation from a safe distance. Look for wobble, mis-tracking, or noise.
- Let engine idle and observe tensioner behavior — should be steady, not bouncing violently.

Post-repair checks
- Re-torque pivot bolt after a short test drive if specified by manual.
- Check belt tension and alignment after a few hundred miles.
- Replace the belt at the same time as the tensioner if belt age/wear is questionable.

Tips, traps and common pitfalls
- Always have the belt routing documented — it’s easy to get the path wrong.
- If the belt had uneven wear, replace both belt and tensioner/pulley(s) together.
- Replace idler pulleys if they are old or noisy; a new tensioner with a bad idler will still cause problems.
- Do not reuse pulleys if bearings are rough; they’re cheap insurance.
- Watch for hidden bolts/fasteners under engine covers and splash shields. Removing the small plastic clips carefully prevents breakage.
- If the tensioner doesn't move easily with a tool, do not force it — inspect for seized pulley/bearing or obstruction.
- Never use pliers on the tensioner arm; use a proper tool to avoid slipping and injury.

When to replace
- Replace tensioner/pulley when bearings are noisy, pulley is wobbling, spring is weak, or during belt replacement if one is old (common recommendation: change tensioner/pulleys every other belt or at roughly 60k–100k miles depending on condition).

What happens if you ignore it
- Faster belt wear, belt squeal, loss of charging (battery light), loss of A/C, loss of power steering assist, potential engine overheating if water pump driven by belt, sudden breakdown if belt breaks.

Final quick checklist before calling it done
- Belt routed correctly and seated on all pulleys.
- Tensioner bolt(s) tightened properly.
- No abnormal noises at idle.
- Accessories operating (A/C, charging, power steering).
- No belt contamination (oil/coolant) present.

That’s the full overview and step‑by‑step you need to inspect, diagnose, and replace the serpentine belt tensioner/pulley on a Jeep Grand Cherokee WH/WK. Follow the vehicle’s shop manual for model‑specific torque values and any special procedures.
rteeqp73

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