I renently purchased my friend's '85 240 DL for $100. It needed a bit of body work to pass inspection, but other than that it is in good shape. The engine has 185k miles on it and it still runs well, though it makes a tapping noise when accelerating. Another friend of mine suggested that it might be the valves tapping. Is there any way I can test this and possibly correct it? Thanks.

the vale clearence in you car is set by shims. It's actually inexpensive to get done. You'd need a set of shims and a micrometer. It's difficult to do for the first time, especially if you're unfamiliar with the process. I think we charge 0.7 hrs for a valve adjustment, plust the cost of a gasket. Shims are included in the labor because we just swap them.