1992 Lexus SC 400FACTORY OEM SERVICE PROCEDURE

Valve Clearance: SC300

  1. With engine cold, turn ignition switch to LOCK and disconnect negative battery cable. Disconnect accelerator cable. On A/T models, disconnect throttle control cable. On all models, disconnect cruise control actuator cable.
  2. Disconnect P/S air hose from No. 4 timing belt cover. Disconnect PCV hose from No. 2 cylinder head cover. Remove air cleaner hose. Remove EGR pipe and gasket. Remove 4 nuts and throttle body bracket.
  3. Disconnect PCV hose, 3 vacuum hoses and VSV (for EGR). Disconnect TPS connector and ISC valve connector. Disconnect sub-TPS sensor connector and sub-throttle actuator connector. Disconnect EGR gas temperature sensor connector.
  4. Remove 4 bolts and 2 nuts holding intake air connector to intake chamber. Remove VSV nut. Disconnect the 2 water by-pass hoses from throttle body and plug hose ends. Remove oil filler cap. With a5-mm hex-wrench, remove the 10 bolts retaining the No. 3 timing belt cover and cylinder head rear cover.
  5. Remove bolt holding the spark plug lead clamp from cylinder head. Disconnect 2 spark plug lead clamps from No. 3 cylinder head cover. Disconnect spark plug leads at the rubber boot. DO NOT pull on the leads. Remove 12 bolts and 4 nuts securing the cam covers, and remove the cam covers and gaskets.
  6. Turn crankshaft pulley and align its groove with "0" timing mark on No. 1 timing belt cover. Ensure that timing marks of camshaft pulleys are aligned with timing marks of No. 4 timing belt cover. If not, rotate crankshaft one revolution (360 degrees) and align marks again.
  7. Ensure cam bearing cap bolts are fully tightened to 14 ft. lbs. (20 N.m), in correct order. See Fig 1.
    Fig 1: Torquing Cam Bearing Bolts (SC300)
    G92F25929Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  8. Measure and record clearance of intake valves on cylinders No. 1 and 4, and exhaust valves on cylinders No. 1 and 5. See Fig 2. Rotate crankshaft pulley 240 degrees (2/3 revolution). Measure and record clearance of intake valves on cylinders No. 3 and 5, and exhaust valves on cylinders No. 3 and 6. See Fig 3. Rotate crankshaft pulley another 240 degrees (2/3 revolution). Measure and record clearance of intake valves on cylinders No. 2 and 6, and exhaust valves on cylinders No. 2 and 4. See Fig 4.
    Fig 2: Adjusting Valves in Proper Sequence - Step 1 (SC300)
    G92D25919Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.