Knowledge of use of limit screws for fd and rd, and barrel adjusters a must for diy bike owners with one by or two bys

Wheels of Happiness

Rizal Philippines

5.18.2021

Happy birthday to my deceased brother Sixto who could be in heaven.   

I gained a lot of experience as did a DIY two by set ups lately;  installing Deckas 34t as the main drive, removing the 42 t, and retaining the 24 granny gear.

You encounter a lot of challenges:   the FD would not shift to the granny gear,  the FD would not shift to the 34t.    The chain falls off and jams the smallest gear (11) and or falls off the largest gear.  Or that the 

gears are noisy.   

How do you deal with them?  Mechanics call it turning

Actions of the limit screws:   fd and rd, and barrel adjuster.

RD (rear derailleur) limit screw

   `1.  Top is the high gear (smallest gear) marked high limit screw, lower one is for the lowest gear

           (marked HI)

         HI - turning clockwise brings the the chain to the left, away from the smallest gear; turning this

                 counter clockwise brings the chain to the right.     Thus if the chain is falling off, you turn

                  the limit screw to the right - clockwise.  If the chain remains at next gear, instead of the 

                  lowest,  you turn the limit screw counter clockwise (to the left)

       LO -  turning this to the left brings the chain further to the left and may cause the chain to fall off

                 So if the chain is falling off, you turn the screw to the right.  If the chain does not shift to 

                 the biggest (aside from the cable being loose) it could be a limit screw maladjustment.  Turn

                 this CCW (the left)

FD.

      HI  - controls the outer movement of the FD, its of the guide relative to the chain ring.    Turning

               this CC brings in the guide inwards and prevents the chain falling off when in high (the

               biggest chain ring)   Turning this CCW (to the left lets the guide move farther to the right.  

               So if the  FD does not allow the big ring shift, you loosen (turn the HI) screw left CCW

    LO  -   controls the movement of the guide relative to the low gear.  (smaller ring).  Turning this 

              CCW (left) moves the guide inwards  nearer the frame.  So if the FD does not shift to the 

               smaller gear, turn this CCW to the left)  If the chain falls off, turn the screw to the right  (CC)

Barrel adjuster:

           Before fixing the cable, turn the adjuster clockwise until it stops and then turn CCW about 4 

            turns for eventual adjustment.   This is used for really fine tuning of the cable especially

            if the gears are noisy. 

           Turning the barrel left  CCW tightens the cable and moves the chain inward;  turning this 

           clockwise moves the chain outward (to the right)   Turn the front barrel adjuster until the noise

            disappears.

Mastering the above is a matter of simplex algorithm - trial and error.