Summary theory (short)
- Valve clearance (lash) is the intentional gap between cam lobe (or rocker) and valve retainer/bucket so that as parts heat and expand the valve fully closes at the correct instant. Correct lash ensures valve seating, correct compression, and correct valve timing and lift.
- Too-tight: valve opens partly at rest or at temp → loss of compression, burning valves, hard start, white/blue smoke, rough idle. Too-loose: noisy tappets, reduced valve opening (less power), possible cam wear and premature tappet wear.
- Two common adjustment systems: screw-and-locknut (adjust on head) and shim-under-bucket (shims sit under cam bucket) — F9Q1/F9Q2 uses shim-under-bucket. Shims are changed to set clearance; you calculate new shim thickness from measured clearance and the target clearance.

Tools and prep (essentials)
- Service manual for exact clearance specs and torque values (use manufacturer numbers).
- Metric feeler gauges, magnetic tool/puller for shims, caliper or micrometer (to measure shim thickness), clean rags, engine oil, torque wrench, basic hand tools, camshaft holding tool or timing pin set, gasket sealant or new cam cover gasket.
- Work on a cool engine if the manual requires cold check (many shim systems are checked cold); follow manual. Disconnect battery.

Ordered procedure (shim-under-bucket type, in logical sequence)
1) Safety & timing marks
- Park, handbrake, disconnect negative battery.
- Bring engine to TDC compression for cylinder 1 and lock timing (use crank pulley mark and cam/chain timing marks). Mark cam caps/shaft orientation and positions so reassembly retains original order.

2) Remove ancillaries and cam cover
- Remove engine covers, intake parts that block cam cover, then remove cam cover.
- Drain any oil from cover area into tray, keep clean.

3) Access camshafts and secure timing
- With timing locked, carefully remove any cam chain tensioner and guides as required by the manual to release camshafts.
- Loosen and remove cam cap bolts in correct sequence, keep caps in order and orientation (mark them). Lift camshafts straight up and support on clean rags (or remove them per manual).

4) Identify valve closed positions
- Rotate engine by 360° as needed so each cylinder’s cam lobes are in valve-closed orientation when checking that cylinder. For each cylinder, you must check when its cam lobes are pointing away (valve closed). Follow the cylinder sequence given in the manual.

5) Measure clearances and shim thickness
- For each valve: remove the bucket (careful — small). Measure the current shim thickness with micrometer and measure the actual clearance (if measuring clearance directly is possible) or calculate.
- Standard calculation: New_shim_thickness = Current_shim_thickness + (Measured_clearance − Target_clearance).
- If you measure actual clearance with feeler between shim and cam lobe, use that reading. If you remove bucket only, measure shim thickness and compute clearance using cam profile methods per manual. (Service manual method is authoritative.)

6) Select and fit new shims
- Use your calculation to pick the nearest available shim size. Clean shim and seat it dry or with a smear of oil as manual advises.
- Refit bucket and ensure it sits flat and the shim is centered.

7) Reassemble camshafts
- Refit camshafts, aligning timing marks. Tighten cam cap bolts in the specified progressive sequence to the specified torque in multiple stages.
- Refit tensioner/components removed. Verify timing marks align and timing is correct (rotate engine by hand two full turns and re-check marks).

8) Final assembly
- Refit cam cover with new gasket/sealant, torque bolts to spec. Reinstall removed ancillaries, reconnect battery.

9) Check and run
- Crank engine and listen: absence of excessive tappet noise, smooth idle. Confirm no oil leaks.
- Re-check valve clearances after a short run if manual requires (some engines recommend rechecking after warm-up/first run).

How the repair fixes the fault (concise)
- Replacing shims to achieve the specified clearance restores the designed gap so valves fully seat and open the designed amount at the correct time.
- If clearance was too tight: replacing with thinner shim (larger gap) prevents valves being held off-seat, restoring compression and preventing burnt valve seats.
- If clearance was too loose: replacing with thicker shim (smaller gap) reduces lash, restoring correct valve lift and timing, reducing noise and recovering engine power.
- Properly torqued cam caps and correct timing ensure cam profiles act on valves as intended; mis-torqued or mis-timed reassembly would reintroduce faults.

Warnings (brief)
- Always follow the factory service manual for clearance targets, shim sizes, torque sequences and values, and whether checks are made hot or cold.
- Incorrect timing or cam cap torques will cause catastrophic engine damage.
- Keep parts clean; no dirt in the valve area.

Done.
rteeqp73

Надежный или неудачный? Разбираем все проблемы дизел... Двигатель F9Q, появившийся в 1997 году на Renault Megane, стал первым французским дизелем с непосредственным ...

Надежный или неудачный? Разбираем все проблемы дизел... Двигатель F9Q, появившийся в 1997 году на Renault Megane, стал первым французским дизелем с непосредственным ...

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