In this type of engine there is no manufacturer set service schedule for checking on the valve clearance, although high mileage or even a noisy valve train may might call for it. Before testing the valve clearances on the hydraulic lifters, the valve cover has to be removed and set the Number 1 cylinder on top dead center of the intake stroke while the exhaust and intake cam lobes face upward. Insert a feeler gauge below the cam lobe of the Number 1 cylinder and measure the thickness of the clearance between the cam lobe and the tappet and record the thickness of the four valves of the cylinder. Then, rotate the crankshaft further to 180 degrees to check clearances of the cylinder Number 3, check the cylinders Number 4 and 2, also. If any is seen to be outside the required range, then it should be corrected and a record of which valves have to be adjusted should be taken on a chart. Examining valve clearances is relatively easy, but adjusting them is quite a problem and this should be done with a micrometer. Should there be changes necessary, other camshaft tappets of different thickness will require to be used and precise measurement has to be done in order to choose the right tappet. If the clearance is to be small, a thin tappet should be installed; while if the clearance is to be large, a thick tappet will do. Once you have established the needful tappets, get them at a local dealership. Place the engine at Top Dead Center, torque the valve cover and front engine cover, take off the 
Timing Chain and both camshaft gears and both camshafts. When having to remove and replace tappets, and there are many, it is advised that they should be done one at a time to avoid mixing them because their faces may be of different thickness. Apply oil on the new tappets that you are going to fit and having fitted them, reverse the process of removing the tappets and before tightening any bolt or nut, oil the cam lover and journals, check and recheck the valve clearances, tighten tappets in the correct sequence followed by torquing every bolt that you tightened, and check all electrical and hose connections for proper connectivity and tightness. To start with, you should take your time and reinstall the engine so as to result to a precise automobile so as to cover up for a leak should there be one.