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-   -   Drivetrain severely off track (https://www.bikeforums.net/bicycle-mechanics/1173185-drivetrain-severely-off-track.html)

Mogens 05-16-19 01:05 PM

Drivetrain severely off track
 
As you'll see, I'm clearly in the "knows just enough to get into trouble,' phase of bicycle mechanics. I rebuilt this Trek 730 for my wife and it needed a new crankset & derailleurs, so I put on a Sugino triple that I had and ordered some Shimano Alti (Altuses?) The rear derailleur is working perfectly, however the FD is clearly incompatible with the crank. The FD won't get anywhere near the largest chainring. So I need a recommendation... different crank? Different front derailleur? What's the best path forward? It's been suggested to me that the derailleur is for MTB/hybrids and the crankset is for road bikes, hence the problem. That makes sense, so I'm looking for a specific recommendation that will definitely work.

https://cimg8.ibsrv.net/gimg/bikefor...511f64e9d6.jpg

mitchmellow62 05-16-19 03:17 PM

Did you install a new bottom bracket? If not, that could be the problem. The spindle may be too long for this crankset placing the chainrings too far away from the seat tube. Someone will probably know the correct numbers or you could do a search to discover the correct bottom bracket/spindle length.

Road Fan 05-16-19 04:55 PM

What exactly do you mean by "off track?" The first thing is to check your installation. Do you know how to measure your front chainline? It should be about 45 mm maybe plus or minus 1 mm, the distance from the center of the down tube to the center of the middle chainring. If that is off you should see if the crank arms are installed correctly (but not over-tightened!) and made right if they are not.

dedhed 05-16-19 06:14 PM

What are the specs on the crankset? AS suggested I suspect your BB is too long and the chainline isn't where it should be.
See if you can find the specs like these for it.
https://www.suginoltd.co.jp/us/produ...g/alpina2.html

Bill Kapaun 05-16-19 06:54 PM

As mentioned, your BB is suspect.
Older cranks tended to use longer spindles than newer stuff.
I went from a 127 to a 113 when I switched to a newer crank.
I had the SAME problem as you.

Jeff Wills 05-16-19 09:16 PM

Need a photo looking down on the crankset from directly above. It would help if the front derailleur is in its furthest outward position.

mixteup 05-17-19 07:50 AM

Agree with all above - That front derailleur should easily handle that triple.
Something else is wrong.

fietsbob 05-17-19 07:59 AM

best is a parallel line thru center of rear cogs* & middle chainring.

* 3 of 5, 4 of 7 , (odd #) etc. or gap between , 4&5 of 8, (even #)

parallel to centerline of bike ..

Mogens 05-17-19 08:39 AM

Cool, that makes sense. I will look into a new bottom bracket. Thanks for the help!


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