Crankcase dowel not in book

Jan 1, 2013
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T140 crankcases have a 5/16" UNC bolt that fastens the upper rear halves, just aft of the inlet cam follower block housing. There is meant to be a thin-walled hollow dowel at that joint. I have one set of cases that has this dowel and on the other set, it's missing (the counterbore for it, both sides is there just as it should be).

The parts book doesn't show or list this dowel. There is no other 5/16" dowel anywhere on the bike, so it isn;t merely a case of getting one meant for something else. All the others are either 1/4" or 3/8"

Anyone got any idea how to get hold of this dowel? Is there anything on a Trident or a Norton or BSA, with a 5/16" dowel?