Hi DD

I actually initially tried standard 1200 manual method, actually it doesn't work on this A12A engine,
So decided to go for Datsun b310 repair manual,and it was damn confusing

Please refer this detail document extracted from it

thanks
regards
sumith

(2) Rotate the engine clockwise as viewed from the front until the number one piston is on tdcon the compression
stroke. In this position the mark on the crankshaft pulley will be aligned with the tdc .

scale on the timing cover and the two valves of number four cylinder will be on the rock. (That is, one just closing
as the other is opening).

The clearances of number one cylinder inlet and
exhaust valves may now be checked and adjusted.
NOTE: Never turn the engine against the normal
direction of rotation or anti-clockwise as
viewed from the front.
(3) To check the valve clearance insert a feeler gauge of the specified thickness between the end of the
valve stem and the adjusting screw. A light drag should be felt if the clearance is correct.
(4) To adjust the clearance, loosen the adjusting screw locknut and using a screwdriver turn the adjusting
screw in the desired direction until a light drag is felt on the feeler gauge. Tighten the locknut.

(5) Check with the feeler gauge to ensure that the clearance has not altered while the locknut was being tightened.
(6) With the valves of number one cylinder correctly adjusted, rotate the engine in the normal direction
of rotation until the valves of number two cylinder are rocking.
With the valves of number two cylinder in the rocking
position adjust both valves of number three cylinder.

NOTE: With the valves of number two cylinderrocking number three cylinder piston is on tdc on the compression stroke.
(7) With the valves of number three cylinder correctly adjusted, rotate the engine in the normal direction
of rotation until the valves of number one cylinder are rocking. With the valves of number one cylinder rocking
adjust both valves of number four cylinder.
Adjusting No.
NOTE: With the valves of number one cylinder rocking number four cylinderpiston is on tdc on the compression stroke.
(8) With the valves of number four cylinder correctly adjusted, rotate the engine in the normal direction
of rotation until the valves on number three cylinder are in the rock position. With the valves of number three cylinder in the rock position adjust the valves of number two cylinder.

(9) With all the valves correctly adjusted instal the rocker cover on the engine using a new gasket. Tighten
the rocker cover securely.