thoughts...
You're missing a lot, John.
I'm a mechanical engineer with over 30 years in the business of precision measurement, so I'll give you my explanation of how the system is supposed to work. I'll first say however, that I installed my first UT crank this spring. After 3500 miles, I've got no sideplay or creaking issues. My crank has worked perfectly all year, on two different frames.
Yes, there is a fixed distance between the bearings, but forget about the Hirth joint. It has nothing to do with the situation. No manufactured product is perfect and there is a chance that a crank could have been produced with a mistake in the overall bearing spacing. I wouldn't jump to the conclusion that this means that any, all or many cranks suffer from such a problem. There also two bearing cups in the system and either one of those could have a dimensional error. Unless you have the factory drawings to know what each component should measure, you're not going to be able to say where the problem lies. The toughest thing to measure would be the distance between the bearings, to verify a problem, but a long internal micrometer would do the job. Measuring the cup thickness between the shell and bearing contact surfaces, is one simple check than anyone with a micrometer could do. If you have several cups around, you could at least compare them for deviations.
Campy specifies that the BB shell width must be 68mm +or - .8mm. If I read correctly, you measured a nearly perfect 68.1mm BB shell width. Did you also verify that the shell faces were square with the threads? Since I don't own expensive BB facing tools, I screw both cups in until they contact a .010 inch feeler gage, then use .008-.012 inch feeler gages to search for high or low spots. Neither of my LOOK 585 frames needed facing to square the faces to the threads.
Another BB shell problem that can occur, but is nearly impossible to fix is misaligned threads. If the threads on each side are not in alignment with each other, no amount of thread chasing or shell facing will fix the problem. Thread chasers merely follow the path of the orginal threads and usually do little but remove burrs, unless the original thread was cut under low limit on the pitch diameter.
One of the confusing issues with the BB cups is the use of Loctite 222 (or not). I've bought two sets of cups this year, for two different frames. Both sets came with a large amount of a yellow thread locker applied to the threads, from the factory. I personally decided to grease the threads of the BB shell and torque the cups in place, rather than use loctite 222. Loctite should only be used on threads that are free of foreign material, so using it without removing the yellow thread locker would not make sense. Also, the yellow thread locker produces so much intereference that it is impossible to hand tighten the cups. Mine required a substantial amount of torque, just to get the cup faces in contact with the BB shell. I would not use Loctite 222 unless I knew the BB faces were not square and also had no way to correct the problem. The loctite is intended to keep the cup faces aligned with the threads, even if faces are out of square, but it won't help if the threads are misaligned. I also think a BB installed with the loctite would be far more prone to creaking, particularly if little or no torque is applied. If the loctite doesn't hold adequately, any small movement of the cup will result in a creak.
The purpose of the wavy washer is simple. It's nothing but a spring to apply a preload force on the bearings and eliminate all freeplay. If the BB width is not within the specified dimensions, then the washer would not produce the desired minimum pressure, or it would produce too much, resulting in binding and/or premature bearing failure. Of course, if there are errors in the dimensions of the crank or the bearing cups, then there could be a problem even with the proper BB shell width. There should never be any actual "freeplay" in the system. When you pushed on the crankarm and got movement, all you were doing is overcoming the spring force of the wavy washer - that's how it's supposed to work! You also mentioned a system that can't compensate for variations in the BB shell width. That's precisely what the wavy washer does. If all other dimensions are correct, then any BB shell in the specified range should produce an acceptable preload on the bearings. The reason that one spindle length can also accomodate a 70mm Italian BB is a no-brainer. The thickness of the cups is just made 1mm thinner on each side, so the nominal distance between the cups faces is the same. Get out your micrometer and compare the two types.
It seems to me that installing any amount of shims merely defeats the intended function of the wavy washer, immediately increasing the preload tension. I'd start with trying a new wavy washer, or better yet a new pair of bearing cups, that includes the washer. Install those and see if it works any better. Of course, if the crank is dimensionally incorrect, the problem will remain.
Be sure that all surfaces of the bearings that contact the cup are greased to prevent creaks. Also don't overlook another common source of creaks, the chainring and bolt area. If I think I've got a creak, the first thing I do is apply some thin lube, like Slick 50 1-lube to eliminate that area as the source.
Now that I've read even further into your posting on the subject, the more I realize you really don't understand the system and just guessed at a fix (adding shims). If you really supected a wear problem with the bearing cups or bearing OD, you should have taken some precision measurements rather than take the shade tree mechanic approach of guessing. Your fix really defeats the system and is likely to ruin the bearings, if they aren't ruined already.
There have been some reports of bearing failures on early model cranks, but changes were made at some point before '08 cranks came out. The latest bearings have plastic rather than metal cages around the balls.
Also, since you're dealing remotely with a customer, be sure the problem is not something totally unrelated like creaky cleats or a creaky saddle. I just put a new saddle on with no lube in the rail area and it's amazing how a creaky saddle clamp can sound just like the BB.
Last, I'll say that you final conclusions are totally wrong, regarding both the Hirth joint and the loctite. Perhaps you should just post your problem details and spare yourself the public display of ignorance (sorry, couldn't resist).
