Life on a Sandbar
Shimano FC M739 Crankset
I have 3 sets of these circa 1998 cranks, and would like some history about them; they don't look much like anything Shimano has put out, and the big ring is part of the spider, essentially requiring one to have to buy the whole sheebang if the big ring is fubar. The series appears short lived, but I am curious if anyone knows the thinking behind this interesting crank.
My 5 arm M739 didn't have the integral big ring/spider (it did have a removable spider that used the same tool that my xtr of the day used). Sounds like yours might have been the 4 arm type, assume similar to the xtr with the integrated big ring/spider, which should be removable by the same tool (but that ring/spider is probably hard to find).
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Do It Yourself
Those cranks were new in 1996 and the first of the 104/64 pattern. They did make the big ring integrated with the spider, same as the M95x series XTR cranks. Shimano went from an engineering perspective with a stiffer integrated setup rather than a user friendly replaceable chainring. This was a brand new bolt pattern optimized for the 22T and 32T rings. Now everyone is using it. The bulged look was new with this model and not far off from the new XT cranks. It was a big transition year that lead to what we have today.
Originally Posted by TraumaARNP
Since you have 3 sets, you should be set for a while but you can replace the spider later if you wanted to. Also, I've seen the big rings for sale on eBay. Honestly, when these wear out you should probably be looking at a newer setup.