Clearance is 0.012" on both intake and exhaust according to my I&T book. First step is to disable the injectors, if your throttle lever stop on shutoff thats fine, if not set it to idle and remove the glow plugs. Removing the plugs will also make the engine easier to rotate. You will need to remove the valve cover which on my 1210 requires some fanagling. Once off you need to rotate the crackshaft so that the valves you're checking are on the compression stroke. You can rotate it by the fan belt, put a wrench on the crank or if you've got a manual put it in it's top gear and give it a push. You can also try hitting the starter but that can be tricky. You'll see one valve actuate and then another. Once the trailing valve has closed rotate a bit past that and check them. You loosen the nuts on the ends of the rockers (above the valve) and slip 0.012" feeler gage between the valve stem and rocker and using a screw driver tighten the bolt till you can just feel some drag when sliding the feeler gage. Take some time and play with the feeler gage, there is a distinctive feel when the gap is correct. Hold the bolt steady with the screw driver and tighten the nut, check to make sure the gage still feels the same and move on. Once you're done reassemble, bleed the injectors a bit if needed and fire it up. You should hear a tiny bit of valve clatter.
