Assembly L20B Rally Spec page 1
Assembly Precautions
Piston
(1) Piston Clearance.
Measure the maximum diameter of the piston, and check whether piston-to-bore clearance is normal.
Pistons are available from grades 1 through 4. If the clearance is less than specified, correction by honing is needed.
(2) Sharp edges inside of piston: Chamfer to 0.2 - 0.3mm (0.008 - 0.012 in).

(3) Difference in weight among cylinders: The difference must be less than 1g (0.04oz). (Piston, piston pin, piston rings and clips).
Number of valve recesses
G2 engine ... One each for intake and exhaust valves.
G4 engine ... Two each for intake and exhaust valves.

(4) Measure the piston ring end gap: Make corrections until the gap meets specifications.
(5) Precautions in assembling piston pin. Before installing the pin, use an oil heater to heat the piston to 40 - 50 degrees C (104 - 122 degrees F).

(6) Check clearance at the valve recess on the top of piston. Place clay on the valve recess before installing the cylinder head, and correctly adjust the valve timing, then turn the crankshaft one complete turn. Check depresssion of the clay, to determine clearance. If abnormal resistance is felt when turning the crankshaft, it is an indication of interference between piston and valve; cease rotation of crankshaft, and correct the valve recess.

This picture shows a G4 piston
L20B Twin cam 16valve
Engine building 2
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