Bike Forums

Bike Forums (https://www.bikeforums.net/forum.php)
-   Bicycle Mechanics (https://www.bikeforums.net/bicycle-mechanics/)
-   -   Another Crank swap question FC-M391 > FC-M590 (https://www.bikeforums.net/bicycle-mechanics/912697-another-crank-swap-question-fc-m391-fc-m590.html)

TakingMyTime 09-13-13 07:41 AM

Another Crank swap question FC-M391 > FC-M590
 
My Trek 7.4fx has a 68mm BB shell. It's stock crankset is a Shimano model FC-M391 with a 48-36-26 tooth configuration. I would like to know if a Shimano FC-M590 Deore Hollowtech II would be a compatible swap? I understand I would have to remove the current BB and install the outboard bearings along with any other related derailleur positioning etc.

Thanks in advance,
TMT

dbg 09-13-13 08:04 AM

The specs say 68 or 73 BB shell but I had problems using this exact model on an older trek-850 (with 68 shell and 130 rear drops). There were not enough spacers to get it installed with the correct and balanced extensions on both sides. I set it aside and ordered a road crank (tiagra I think) because I wanted the best Q. I have since installed it into a 73 BB shell and it fit perfectly.

joejack951 09-13-13 08:17 AM


Originally Posted by dbg (Post 16061133)
The specs say 68 or 73 BB shell but I had problems using this exact model on an older trek-850 (with 68 shell and 130 rear drops). There were not enough spacers to get it installed with the correct and balanced extensions on both sides. I set it aside and ordered a road crank (tiagra I think) because I wanted the best Q. I have since installed it into a 73 BB shell and it fit perfectly.

How many spacers did you try to use for the 68mm shell? The crankset/BB should have included three 2.5mm spacers for use with a 68mm shell and a standard (non-E-type) front derailler. How many spacers did you use for the 73mm shell? There should be only one on the drive side.

To the OP, the Deore crank should swap in just fine. You might not even need to adjust your front derailler if you get lucky enough. Read the instructions and install the appropriate spacers to ensure proper preloading of the bearings and chainline. A 68mm shell gets one 2.5mm spacer on the non-drive side and two of the same spacer on the drive side.

TakingMyTime 09-13-13 08:49 AM


Originally Posted by joejack951 (Post 16061181)
To the OP, the Deore crank should swap in just fine. You might not even need to adjust your front derailler if you get lucky enough. Read the instructions and install the appropriate spacers to ensure proper preloading of the bearings and chainline. A 68mm shell gets one 2.5mm spacer on the non-drive side and two of the same spacer on the drive side.

Thank you. From everything I could tell I believe you are correct. I just wanted to make sure there wasn't anything I was missing. I understand about the spacers and have seen their positions on the PDF from Shimano.

dbg 09-13-13 01:46 PM


Originally Posted by joejack951 (Post 16061181)
How many spacers did you try to use for the 68mm shell? The crankset/BB should have included three 2.5mm spacers for use with a 68mm shell and a standard (non-E-type) front derailler. How many spacers did you use for the 73mm shell? There should be only one on the drive side.

Done per instructions left it off center (one crank arm farther from the chainstay than the other side). Stacking spacers to center crank arms left way less purchase on the threads on one side. Frame (chainstays) seemed to measure in perfect alignment, and the subsequent similar road Tiagra crankset installed in that frame perfectly. AND the Deore later installed perfectly as per instructions into a mtb 73 shell. I'm pretty thorough and analytical by nature so the whole thing had me scratching head.

Good luck. Post success story --so I can second guess myself forevermore.

[edit: am anticipating someone suggesting I was confusing DS and nonDS. I'm not going back to disassemble two bikes to check, but I can't help thinking that myself --in retrospect]


All times are GMT -6. The time now is 10:44 AM.


Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.