That info is on the Emission Sticker.
Otherwise there is a forumla to ad clearance somewhere in the DIY section:
DIY Repair Links
http://www.peachparts.com/shopforum/forumdisplay.php?f=82
http://www.peachparts.com/Wikka/DoItYourSelf

Another way would be to do a hot Valve Adjustment.

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84 300D, 82 Volvo 244Gl Diesel