ok, you're half right. That's the rocker cover, the rockers push on the valves to open then, if there's no clearance between the rocker and the valve then you lose compression because the valve is being held open all the time. The solution is to set the valve clearance.
You don't have to remove the rocker cover to fix it, that what the valve inspection covers at the top and bottom are for. you should set them at .003 for the inlet valve (the top one) and .004 exhaust (bottom one).. make sure you don't get confused and set them at .03/.04
You don't have to remove the rocker cover to fix it, that what the valve inspection covers at the top and bottom are for. you should set them at .003 for the inlet valve (the top one) and .004 exhaust (bottom one).. make sure you don't get confused and set them at .03/.04