valve clatter

Since I bought my XS400, I've been slowly doing all of the major maintenance items. This weekend I finally got around to changing the oil and filter and setting the valve clearances. Before I touched it it was running perfectly and sounded great.

When I tore it down, I was horrified to discover that the valve clearances were *very* tight...like close to zero mm.

So I drained the oil, changed the oil filter, filled it up with 20W/50, set all four valves to the specs called for in my shop manual. I put it all back together, fired it up, and now the valves clatter like crazy. They're *almost* as loud as the exhaust (although I admit that the exhaust note produced by a 400CC street bike with stock mufflers isn't exactly deafening). I drove it to work yesterday and it rattled away all the way there and back.

So, what's the dilly-yo-yo?

• Did I mess up the clearances?
  Maybe, but I don't think so.
• Do those engines just make a bunch of valve clatter when in spec?
  Maybe...but it sure is clattery for a healthy engine
• Is the engine assembled in such a way that the TDC marks on the crank don't actually correspond to TDC so I set the valve gap when they were supposed to be partially open?
  Maybe...but this is doubtful too because with the spark plugs removed, operating the kick starter would make the engine settle pretty darned close to the TDC mark, like the mark corresponded to the valve springs shoving the cam to that position...(i.e. where there is no cam lobe, i.e. where both valves should be closed, i.e. TDC).
• Did the previous owner have it filled up with super-thick oil to mask some clattery mechanical problem?
  I sure hope not...he really didn't seem like a slimy con man, so I kind of doubt it.

So, my plan is to open up the valve inspection covers again, have my wife kick it over while I watch the lifters to make sure that the TDC marks really correspond with when the valves close. Then I'll double-check my clearances.

In any case, I'm glad that "a tappy valve is a happy valve" and that I'm not in any danger of burning out my exhaust valves from excessive clearance...but I would feel better if the engine sounded more like a purring vicious animal than a clattery Model T.