Have a look under the oil filler cap to see if there is any splash on the top end, if its dry you have issues, but tappity top end is often caused by blockages in the feed to the lifters, so you might have good pressure to the rest of the engine. I recommend an oil flush with a thiner oil if thats the case, often that will sort it. Or you may have one or more knackard lifters, a whole set is arround £30 on ebay. Rare to have pressure problems on these engines. Do you know if its just one or all the lifters tapping?