1) Big-picture theory (why valve lash exists)
- The 4Y is a pushrod (overhead valve) engine: camshaft lobes lift lifters → pushrods → rocker arms → open valves. Valve lash (clearance) is the intentional gap between the rocker and the valve tip (or tappet) when the valve is fully closed.
- Lash compensates for thermal expansion, cam and valve-train geometry, and ensures valves fully close at operating temperature. If lash is too tight, valves can be held open (loss of compression, burned valve seats). If lash is too loose, you get noisy tappets, increased wear, and eventual timing/flow loss at higher rpm.
- You must measure and set lash with the engine cold and with the particular cylinder at the compression-stroke Top Dead Center (TDC) so both intake and exhaust valves for that cylinder are fully closed (no cam lift).

2) Symptoms fixed by correct adjustment
- Excessive valve noise (ticking): caused by excessive clearance; corrected by reducing lash to spec.
- Rough idle, poor throttle response, power loss or misfires: can be caused by either excessive or insufficient lash (insufficient lash prevents valves sealing; excessive lash reduces effective valve opening time).
- Exhaust popping, high fuel consumption, burnt valves or seats: result from valves running partially open (lash too tight) and are prevented by restoring correct clearance.

3) Tools and preparation (short)
- Basic tools: metric/open-end or box wrenches for rocker adjuster and locknut, feeler gauge set, socket for crank pulley and/or ratchet to turn engine, screwdriver, rag, torque wrench for valve cover.
- Remove valve cover, clean area so no debris falls into head. Remove air cleaner if it restricts access.

4) How to determine the adjustment points (order)
- Find TDC on compression stroke for cylinder 1 by aligning crankshaft timing mark to the TDC pointer. Confirm compression stroke (both valves closed) by either:
a) observing that the rocker arms for cylinder 1 are loose/not being pushed up, or
b) removing the spark plug for #1 and rotating the crank while feeling for compression with your thumb (optional).
- When #1 is at compression TDC, the paired cylinder valves that are also on closed overlap in this engine are #4. So adjust valves for cylinders 1 and 4 at this position.
- Rotate the crank 180 degrees (one half turn) to bring the other pair (cylinders 2 and 3) to compression TDC and adjust those.

5) Step-by-step adjustment procedure (in-order, with the theory for each action)
1. Clean around the valve cover, remove valve cover. Rationale: prevent contamination.
2. Rotate engine to TDC compression for cylinder 1 (align crank mark). Rationale: ensures the cam lobe for that cylinder is on its base circle so valve is fully closed.
3. Identify rocker adjuster and locknut for cylinder 1 intake. Loosen locknut enough to turn the adjuster. Rationale: free the adjuster so clearance can be set.
4. Insert the correct feeler gauge between the rocker pad and valve tip (or the adjuster and stem tip depending on design). Theory: the feeler represents the desired thermal clearance so you set the gap at cold.
5. Turn the adjuster until you feel a slight drag on the gauge, then hold adjuster while tightening locknut. Theory: slight drag ensures the clearance is neither too tight (no drag) nor too loose (no drag + rattle).
6. Re-check the gap after the locknut is tightened (locking can shift the adjuster). Theory: confirm the final clearance is still within tolerance.
7. Repeat for the exhaust valve of cylinder 1 (and then for both intake & exhaust on cylinder 4 while still at #1 TDC). Rationale: those valves will be closed; cam lobes are on base circle.
8. Rotate crank 180° to bring cylinders 2 & 3 to compression TDC. Repeat the adjuster-loosen → gauge → set → locknut → recheck steps for #2 and #3 intake and exhaust valves.
9. After all valves are set, rotate the engine by hand two full revolutions and re-check all clearances. Theory: this ensures no seating shifts and nothing binds through the cycle.
10. Reinstall valve cover with fresh gasket or RTV as required and torque to spec. Start engine, listen for abnormal noise, and recheck after a short run if needed.

6) What to expect after repair and reasons it fixes faults
- Noise reduction: correcting excessive lash removes the mechanical gap that causes tappet click.
- Restored compression and power: correcting too-tight lash lets valves seat fully (restores sealing), correcting too-loose lash restores proper valve timing and lift effective area.
- Longevity: correct lash reduces abnormal wear on cam lobes, rocker pads, valve stems, and seats—preventing burned valves and costly repairs.

7) When adjustment alone won't fix it (what the theory implies)
- If you cannot obtain/specify correct lash because an adjuster bottoms out or you must set an unusually large gap, that implies component wear (worn cam lobes, lifters, bent pushrods, valve guide wear, or burnt seats) and requires replacement/valve-job.
- If a valve won’t seat even with correct lash, the seat is likely damaged and needs regrinding or replacement.

8) Final checks and good practice
- Always adjust cold. Adjusting hot masks thermal expansion and causes improper seating at operating temperature.
- Re-check after a few hundred miles; new parts or reworked seats may settle.
- Keep a record of lash values and interval—periodic checks prevent progressive damage.

No extra questions.
rteeqp73

Rebuilding our Toyota 4Y Engine at home | VANLIFE We complete an engine rebuild on our 1987 4Y Toyota Hiace Engine ourselves. Starting with removing the motor through the ...

4Y ENGINE Capacity: 2237 cc 4400 rpm eight-valve 94 hp.

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