Short, ordered, theory-first explanation and procedure. I include both adjustment methods because 5L-series installations can be either screw/locknut rocker arms or shim-under-bucket (confirm by inspection). Always use the factory valve-clearance specifications and torque values for your specific 5L-E; I show typical practice but not a guaranteed number.

Theory (why valve clearance matters)
- Valve clearance (lash) is the small gap between valve train parts when the valve is closed. It compensates for thermal expansion of the head, valves, cam and rocker during operation.
- If lash is too tight: valves start to stay partly open at operating temperature → loss of compression, poor idle, low power, hot valves (burnt valves), rough running, white/black smoke, possible valve-seat damage.
- If lash is too loose: noisy ticking, increased cam/rocker wear, reduced valve lift/duration (marginally), and eventual accelerated wear or broken components.
- Adjustment restores the intended valve timing and lift relationships, re-establishes compression and sealing, and eliminates excessive noise and wear.

How to tell which adjustment system you have
- Look under the valve cover:
- If you see an adjusting screw with a locknut on each rocker arm: it’s the screw-and-locknut (mechanical) system. Adjust by turning the screw and locking the nut.
- If rocker tops are smooth and there are round buckets/caps under the cam with no screw: it’s shim-under-bucket. Adjustment is done by measuring clearance and changing shims to obtain correct clearance.

Tools & prep (minimal list)
- Factory service manual (clearances, torque specs, firing order)
- Feeler gauges (metric set)
- 10–17 mm wrenches/sockets (for locknuts/covers)
- Screwdriver or hex driver for screw adjusters if present
- Torque wrench (for valve cover and any specified fasteners)
- Clean rags, solvent, new valve cover gasket if needed
- Crank turning tool (socket on crank pulley)
- Gloves, eye protection

General ordered procedure (step-by-step) — do not skip verifying which system you have

A. Common initial steps (both systems)
1. Cold engine: do adjustments on a cold engine unless the manual specifies “hot.” (Most Toyota L-series specify cold.)
2. Remove engine covers and intake parts necessary to access the valve cover. Disconnect battery if you will be working around wiring.
3. Remove valve cover and clean sealing faces and make sure no dirt drops into the head.
4. Identify cylinder 1 and confirm firing order (inline-4 Toyota standard: 1–3–4–2). Rotate engine by hand to the required position for cylinder 1 on the compression stroke (cam lobe base circle for both valves).

B. Screw-and-locknut rocker adjustment (if present)
5. Bring cylinder 1 to TDC compression stroke: both intake and exhaust rockers sit on the cam base circle (valves fully closed).
6. Using the correct feeler gauge thickness for intake (factory spec) slide the gauge between rocker tip and valve stem/adjuster. Note feeler gauge should have slight drag but be able to slide without force.
7. If clearance is out of spec:
- Loosen the locknut.
- Turn the adjuster screw until the feeler gauge has the correct drag.
- Hold the adjuster and tighten the locknut while holding the adjuster position; recheck clearance after tightening.
8. Adjust exhaust and intake for cylinder 1.
9. Rotate the crank to bring the next cylinder in the firing order to TDC compression (1→3→4→2). Repeat steps 6–8 for each cylinder in firing order until all valves are adjusted.
10. After all adjusted, re-torque any locknuts to specified torque, clean up, replace valve cover gasket and valve cover, torque valve cover bolts to spec.
11. Start engine, listen for abnormal noise, run to operating temperature, recheck if manual recommends.

C. Shim-under-bucket method (if present)
5. Bring cylinder 1 to valve closed / base circle for lobe under the bucket. You must position cam so the bucket for the valve is resting on cam base circle (both valves closed for that cylinder).
6. Use feeler gauge between bucket top and rocker/cam follower surface (or measure lash per manual). If clearance out of tolerance, you must remove the camshaft or rocker/retainers per manual to access the shim.
7. With shim removed, measure thickness and calculate new shim thickness = measured thickness + (actual clearance − desired clearance). Replace with nearest available shim and reassemble. (Some procedures allow using a selector plate if available.)
8. Reinstall cam/rockers, torque to spec, rotate engine and re-measure. Repeat as needed across cylinders. Shim replacement is iterative and requires correct inventory of shim sizes.
9. Reassemble valve cover and ancillary parts, torque to spec.
10. Start engine, listen and recheck as required.

How the repair fixes faults (concise)
- Resetting lash restores full valve lift and correct valve timing profile: this improves sealing at overlap and compression, restoring power and idle stability.
- Correct clearance prevents valves from being held open (fixes low compression and misfire) and reduces metal-on-metal impact (stops ticking and reduces cam/rocker wear).
- For tight valves that become burnt, adjustment stops further damage but does not repair already-burnt valves; if compression is still low, further diagnosis (leakdown, valve inspection) is needed.
- For shim-type trains, replacing worn/incorrect shims returns the contact geometry and clearance; for screw-type trains, tightening the adjuster corrects the gap directly.

Common pitfalls and checks (short)
- Always verify you’re on the compression stroke (both valves closed) before measuring.
- Don’t overtighten locknuts; they can change the adjustment or damage threads.
- Recheck clearance after tightening the locknut — locknut tightening often changes lash.
- If a valve is grossly out of spec and won’t come into range by the available shim sizes or adjuster, inspect for cam lobe or rocker wear, bent valve or improper assembly.
- Replace valve cover gasket if brittle to avoid oil leaks; keep dirt out of the head.

Outcome you should expect
- Quiet valve train, stable idle, restored power and improved emissions/consumption if the cause was valve lash. If symptoms persist, test compression/leakdown and inspect valves/cam for wear.

End.
rteeqp73

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1) Preparation and safety
- Action: Park on level ground, engine cold, parking brake on, wheels chocked. Disconnect negative battery terminal if you’ll be near electrical connectors or working on the alternator. Gather tools: socket set, breaker bar/long handle, pry bar or tensioner tool, belt gauge (optional), torque wrench, penetrating oil, flashlight, rags.
- Theory: Prevents accidental engine start, electrical shorts and injury. Proper tools let you apply controlled force and measure tension.

2) Diagnose and document
- Action: Note symptoms (squeal, poor charging, overheating, A/C poor). Photograph or sketch the current belt routing and accessory positions before removal.
- Theory: A belt transfers torque from the crank to accessories. Symptoms indicate belt slip, glazing, or failed tensioning. Routing reference prevents mis-installation.

3) Inspect belt and accessories before removal
- Action: Visually inspect belt for cracks, fraying, missing ribs, glazing, polished edges, embedded debris. Spin each pulley by hand (with engine off) and feel for roughness or play; check for oil/coolant on pulley faces.
- Theory: Cracks and glazing reduce friction and flex life. Pulley bearing play or contamination causes misalignment and rapid belt wear; fixing belt only will fail if pulleys are bad.

4) Release belt tension and remove belt
- Action: Identify tensioner type (automatic spring-loaded or manual adjuster). Use the correct tool to rotate the tensioner and relieve tension, then slip belt off an accessible pulley and fully remove.
- Theory: The belt must be released without forcing pulleys. Automatic tensioners maintain correct dynamic tension; manual systems depend on proper pre-load setting.

5) Inspect and, if needed, remove accessory mounting hardware
- Action: Check alternator/idler/tensioner mounting bolts for corrosion or looseness. If pulley or tensioner replacement needed, remove those components per service procedure.
- Theory: Worn mounting hardware or loose components will cause misalignment and premature belt failure.

6) Inspect pulleys and alignment
- Action: Use a straightedge or visual line to confirm pulleys are co-planar. Check idlers and tensioner pulley for smooth spin and no axial play.
- Theory: Misalignment causes edge wear and uneven loading; straight alignment ensures the belt rides correctly across ribbed surfaces.

7) Clean pulley grooves and check for contamination
- Action: Wipe pulleys clean; remove oil, coolant, dirt. Trace the source of any oil/coolant and repair leaks (water pump, valve cover gasket, power steering).
- Theory: Contaminants reduce coefficient of friction between belt and pulley causing slip and glazing.

8) Select correct replacement belt and components
- Action: Fit OEM or quality aftermarket belt with the correct number of ribs and length for the 5L‑E. Replace automatic tensioner and idler(s) if aged, noisy or seized.
- Theory: Correct profile and length ensures full contact area and correct routing. Tensioner/idler springs and bearings wear out; replacing them restores correct dynamic tension and reduces risk of repeated failure.

9) Route new belt
- Action: Follow photographed routing. Loop belt around pulleys per routing chart, leaving the tensioner/accessible pulley for last.
- Theory: Proper routing makes sure each accessory receives designed torque; wrong routing can damage accessories or cause belt to jump off.

10) Apply tension and set static tension
- Action: For automatic tensioner: rotate tensioner, slip belt on, release to apply tension. For manual systems: use the adjustment bolt to apply specified tension. If available, use a belt tension gauge or measure deflection with a specified load (typical method: ~10–15 mm deflection at mid‑span with ~10 kg load; use manufacturer spec if available).
- Theory: Static tension prevents initial slip and ensures the belt starts with enough preload to transmit torque. Automatic tensioners provide dynamic compensation for belt stretch and loading; manual tension must be set to allow proper deflection under load.

11) Verify alignment and seating
- Action: Visually confirm the belt sits fully in each pulley groove and is centered. Spin the tensioner and accessory pulleys by hand to ensure smooth travel.
- Theory: Proper seating prevents edge lift and local overload; smooth pulley travel indicates no bearing seizure.

12) Torque mounting bolts to spec
- Action: Tighten alternator/idler/tensioner bolts to Toyota torque specs (consult manual) and lock any adjusters with their lock nuts.
- Theory: Proper torque prevents movement and retains alignment under load. Under-torqued bolts can shift and misalign pulleys; over-torqued bolts can damage threads or components.

13) Reconnect battery and run engine test
- Action: Reconnect battery, start engine, listen for squeal, watch for belt tracking and vibration, observe charging voltage and accessory operation, check for leaks.
- Theory: Running under load verifies the belt transmits torque without slip and that accessories are functioning. Immediate reassessment catches installation errors.

14) Re-check tension and re-inspect after a short run
- Action: After a few minutes of running and one short drive, shut down and re-check belt tension and pulley condition; retorque mounting bolts if necessary.
- Theory: New belts seat and stretch slightly; re-checking ensures tension stays within range and nothing loosened.

How the repair fixes faults (mapping symptoms to mechanisms)
- Squealing on start/acceleration: Caused by low tension, glazing, or contamination. New belt + correct tension restores friction and stops slip-related noise.
- Battery not charging/low alternator output: Slip under load reduces alternator speed. Restoring belt integrity and tension restores torque transfer so the alternator reaches proper RPM.
- Overheating or coolant loss (if belt drives water pump): Slip reduces pump flow. New belt restores pump speed and coolant circulation.
- Belt shredding or fraying: Caused by misalignment, damaged idler, or contaminated belt. Replacing belt and correcting pulley alignment or replacing bad idler stops further damage.
- Rapid belt wear after replacement: Usually due to bad tensioner/pulley or oil/coolant contamination. Replacing those parts and fixing leaks prevents repeat failures.

Key theoretical principles (brief)
- Friction and contact area: Belt transfers torque via friction between ribs and pulley grooves; contact area and surface condition control available torque before slip.
- Tension and preload: Static tension prevents initial slip; dynamic tensioners keep tension within operating range despite stretch and thermal changes.
- Alignment: Co-planar, concentric pulleys distribute load evenly; angular/parallel misalignment concentrates stress at edges.
- Material fatigue: Belts age by flexing (crack propagation) and environmental contamination; replacing a fatigued belt restores elasticity and rib integrity.

Common pitfalls to avoid
- Reusing a glazed or contaminated belt — it won’t bite even if tensioned.
- Ignoring worn tensioner/idler bearings — they cause rapid new-belt failure.
- Incorrect routing or missing an under/over wrap — leads to accessory failure or belt jump.
- Not rechecking tension after initial run-in — new belts seat and may require slight retensioning.

Done.
rteeqp73