Mine holds just fine, they dont need to be super tight, just as long as the cap wont spin in the yolk, otherwise, they fail, and usually wear the yolk out as well, thats probobly why mines loose, and needs shims, I havent tried, but if I find new clamps, it might fix it.
I bet they are the wrong ones, I bet the "Internal" ones he mentioned are the right ones. I have learned in the past, when 2 different parts are called for, if its not too expensive, buy both and bring the one you didnt use back.