weak compresion on 1&2 cylinders

[artc]

valve lapping is done after the valves and seats have been ground to insure a correct fit, not as a corrective measure for low compression.


you can adjust the valves if they have worn in and are too tight, perhaps causing your low compression issue. but if that is the case, then while you have the head off you might as well grind the valves properly.

i would remove the oil pan and one piston to check ring clearances and bearings. that will tell you a lot.