no gap on tappets on v8

hi i have a 1988 3.5v8 on lpg r/r claasic. i noticed that i can here a ticking noise tapping noise intermittant comming from the drivers side of the rocker cover. so i removed it thinking i could adjust the gap between the valve stem and rocker only to find no adjuster. so i have turned the engine over by hand untill rocker on the far back of the engine was down and went to check gap on cylinder rocker near the front and there is no gap on any of them is this right,because i thought there should be a feeler gauge gap or are they preset like that. any advice on this will be good thanks

You have hydraulic tappets therefore maintenance free and quiet operation of the inlet and exhaust valves. It utilizing engine oil pressure to eliminate the mechanical clearance between the rockers and the valve stems.

oh OK thanks

but they do feck up..as do rocker arms, cam.. etc..