Bicycle Mechanics - Shimano Crankset Upgrade

I'm servicing a Mtn Bike which has a Shimano "comfort bike" FC-C051 Crankset (single piece chainrings). The owner asks if it can be converted to replaceable chain rings. Researching Shimano's Web Resources shows that the Alivio and Deore Cranksets both use a four sided spline to bolt onto the axial which appears to be identical to the FC-C051 four-sided spline attachment.

Does anyone have experience with this (or similar upgrades)? Any thoughts are greatly appreciated. Note: the bottom bracket appears to be a generic "house" brand, however it is doing a nice job with the Shimano FC-C051 Crankset.

Note: I will obtain a Front Derailleur to match the Alivio or Deore conponent. Rear components will remain as is.

Thank you for your wisdom.

It's called a tapered spindle. Unless you also plan on changing out the BB you have to match the new cranks recommended spindle length to the spindle length that's already there, otherwise the chainline,chainstay clearance,and ability of the derailer to shift the rings gets messed with too .Cranks and recommended spinldle lengths are in the QBP catalog.You cannot always just mount a different crank even though the spildle will acomodate it.There is much more to consider. No point in changing the front derailer if you stick with the same or nearly the same tooth count on the big ring on the replacement crank.

If the existing cheapo crank is secured with a nut instead of a bolt, you will definitely need to replace the spindle, and perhaps the entire BB assembly. [This is a great opportunity to switch to a modern sealed-bearing cartridge.] If it uses a bolt, then you MAY be able to use the existing spindle, but there are two variables: 1) there are two taper end standards for 4-sided crank spindles (many Shimano models vs. almost everyone else); 2) the lateral position of the crank and spider, relative to the mounting hole. Sheldon Brown is starting to assemble a data base regarding how far various cranks assemble onto various spindles, but the specific data you require may not yet be available.

John,why muddy the water.Nut and blot types can have the same taper, and can maesure the same end of taper to end of taper.The post dealt with fairly current shimano stuff so iso,vs JIS taper is not an issue.The real issue is spindle length.And even if there was a ISO/JiIS taper mismatch people have run the mismatch and never known the difference.Simply stated both tapers are the same 2degrees, but the ISO starts and ends smaller than the JIS.That means a iso crank won't go on a jis spindle as far as is should, and a jis crank will go on a iso crank a little further than it should.The mismatch can be run,but once done it should not be switched back the other way.