Checking and Adjusting Engine Valve Clearance

Too little valve clearance throws valves out of time. Valves open too early and close too late. This causes the valves to overheat due to hot combustion gases rushing past valves when out of time. Overheating lengthens valve stems which prevents proper seating of valves. The valves seat so briefly or poorly that normal heat transfer into the cooling system does not have time to take place, causing burned valves and low power.

Too much valve clearance causes a lag in valve timing, causing engine valve train imbalance. The fuel-air mixture enters the cylinders late during intake stroke. The exhaust valve closes early and prevents waste gases from being completely removed from cylinders. Also, the valves close with a great deal of impact, which may crack or break the valves and scuff the camshaft and followers.

IMPORTANT: Valve clearance MUST BE checked and adjusted with engine COLD.

1. Remove rocker arm cover with ventilator tube.

IMPORTANT: Visually inspect contact surfaces of wear caps and rocker arm wear pads. Check all parts for excessive wear, breakage, or cracks. Replace parts that show visible damage.

2. Remove plastic plugs from cylinder block bores as shown and install JDG820 Flywheel Turning Tool and JDE81-4 Timing Pin.

3. Rotate engine with the flywheel turning tool until timing pin engages timing hole in flywheel.

If No. 1 cylinder rocker arms are loose, the engine is at No. 1 "TDC" Compression Time.

If No. 6 cylinder rocker arms are loose, the engine is at No. 6 "TDC" Compression Time. Rotate the engine one full revolution to No. 1 "TDC-" compression time.

NW270730

Remove Plug

RG,RG34710,4085 -19-01JAN96-1/3

4. With engine lock-pinned at "TDC" of No. 1 piston's compression stroke, check valve clearance on No. 1, 3 and 5 exhaust valves and No. 1, 2, and 4 intake valves.

Intake Valve Clearance Checking (Rocker Arm-To-Valve Tip With Engine Cold) - Specification

Clearance - 0.41-0.51 mm (0.016-0.020 in.)

Exhaust Valve Clearance Checking (Rocker Arm-To-Valve Tip With Engine Cold) - Specification

Clearance - 0.66-0.76 mm (0.026-0.030 in.)

5. Turn steering wheel 360° until piston No. 6 is in its "TDC-" compression time. Rocker arms for No. 6 piston should be loose.

6. Check valve clearance with the same specifications on exhaust valves 2, 4 and 6 and intake valves 3, 5 and 6.

NOTE: Adjust valve clearance in the same sequence used for checking clearance.

7. If valve clearance needs to be adjusted, loosen the lock nut on rocker arm adjusting screw. Turn adjusting screw until feeler gauge slips with a slight drag. Hold the adjusting screw from turning with screwdriver and tighten lock nut to specifications.

Valve Adjusting Screw Lock Nut- - Specification

Torque -Value 27 N·m (20 lb-ft)

Recheck clearance again after tightening lock nut and compare to the following specifications. Readjust clearance as necessary.

Intake Valve Clearance Adjustment (Rocker Arm-To-Valve Tip With Engine Cold)- - Specification

Clearance - 0.46 mm (0.018 in.)

Exhaust Valve Clearance Adjustment (Rocker Arm-To-Valve Tip With Engine Cold)- - Specification

Clearance - 0.71 mm (0.028 in.)

RG5241

Adjust Engine Valve Clearance (If Needed)

RG4295

Valve Adjusting Sequence

RG,RG34710,4085 -19-01JAN96-2/3

8. Install rocker arm cover and tighten cap screws to specifications.

Rocker Arm Cover-To-Cylinder Head Cap Screws - Specification

Torque -Value 8 N·m (6 lb-ft) (72 lb-in.)

RG,RG34710,4085 -19-01JAN96-3/3