I have a 1963 122 wagon with a B18 engine. It has generally run very well, but yesterday it suddenly stareted making a "ticking" or clattering noise which is very loud at idle but disappears as rpm climbs. The noise started out fairly quiet, but within a few minutes of driving became quite loud.

I pulled off the cam cover but found nothing amiss. The valve clearances are loose but not too bad. The noise sounds like it is coming from the #1 cylinder or from inside the timing cover. And when I turn the engine over by hand I hear a "click" about once every half-revolution that sounds like something loose in the timing cover.

If I loosen the fan belt and just spin the fan I don't hear anything amiss (so it doesn't seem to be a water pump problem). The oil level is a little too full (maybe 1/2 qt) but it doesn't overheat and the oil pressure light doesn't come on.

Any suggestions? I'll take the timing cover off next and poke around but some idea of what might be going on would be nice first. Thanks.