Yes - there are several tolerances that "stack up" in this case. A quick discussion of thread design and terminology may be appropriate here also. A 22 mm dustcap thread is about 21.9 mm at it's Major (largest) diameter. There are three diameters for any thread: Minor, Pitch, and Major (going from the smallest to the largest). When you refer to a dustcap thread as being 22 mm, that is the Major diameter that you are talking about. The pitch diameter is midway between the minor and major diameters. Pitch is the distance from one thread's peak to the next (about 1 mm in our case). The minor diameter, for an internal thread such as in a crank arm, is what any tool must clear (to be used to remove the crank arm bolt, in our case). This is smaller than the Major diameter by approximately two times the thread depth (from root to crest), and is about 20.9 mm in our case. So you can't insert a 22 mm diameter tool into a 22 mm internal thread - it has to be 20.9 mm max. (actually even a bit smaller that that, because of the locational and size tolerances on the bolt head itself, the various tolerances of the crank arm threads, as well as the locational and fit tolerances of the bolt thread in the spindle threads, and even manufacturing tolerances of the tool in question). YAMMV. Greg "Geek Squad Charter Member" Parker Ann Arbor, Michigan P.S.: Crank arm dustcap / extractor threads: 22mm x 1mm = darn near everybody 23mm x 1mm = TA 23.35mm x 1mm = Stronglight 7/8" x 24 TPI = early Lambert 22 x 1 mm Left-hand-thread: C-Record, CDA, Victory
P.P.S.: I just realized that Sutherland's mentions the Zeus scenario specifically on page 2-3 of the Fifth Edition, giving a 20.8 mm max. tool O.D., and stating that "if you ever get the bolt out, use a 15mm bolt instead." Yet another reason to have a copy of Sutherland's!
Date: Fri, 3 Dec 2004 18:36:02 -0800 (PST) From: Neill Currie <neill1234@yahoo.com> To: classicrendezvous@bikelist.org Subject: [CR]Re: Park 16mm wrench - Deciding vote?
If the hole is 22 and the wrench 21.8 it MAY still not work. It may go into the hole easily, but not fit over the bolt head(though it may/will fit over the bolthead if the bolt is not inside the crank at the time).........depending on manufacturing tolerances, eccentricities in centres of the spindle/crank/bolthead.........and also the state of the moon ;-)
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Neill Currie
595-B E. Deering Rd
Deering
Nh 03244
tel: 603-529-6472