We recommend using your local bike shop for installation as these instructions do not cover unique removal procedures for critical drivetrain components.
Read through the entire instructions before installing! Due to the modular nature of the Rock Bottom certain steps may require the removal of your cranks. Understanding the instructions will avoid needing to remove the cranks multiple times.
We recommend installing the Rock Bottom frame using a bike stand.
Remove the cranks from your bike on the drive side following the crank manufacturer’s instructions and clean around the bottom bracket and ISCG tabs.
Install the Rock Bottom guard onto the Rock Bottom frame using the provided low profile M6 screws and torque to 3Nm.
Loosely install the Rock bottom guard to the Rock Bottom frame using the low profile M6 screws provided with the ISCG05 frame. You will adjust the position later.
Mount the chain guide arm using the 3 provided M3 countersunk screws. Tighten each gradually while alternating screws multiple times before torquing to 0.2Nm.
Remove your bike from the stand if using one and set it tire side down. Never apply force to the guide arm. Do not use the guide arm to rotate or restrain the Rock Bottom when adjusting the frame angle.
Adjust the rotation of the Rock Bottom until the Standard Chain-Line guide arm is vertical. Torque the ISCG05 M6 mounting bolts to 7Nm. *If using the High Pivot guide the arm will be at approximately 45° but is frame dependent so leave the M6 screws loose.
Place your bike back into the stand if available and reinstall your cranks according to the manufacturer’s directions.
Reinstall the chain onto the chainring and shift to the largest cog.
Eyeball the chain guide spacing by pinching it against the guide arm. If necessary snap a shim on the back with the nub facing out and insert the M5 mounting screw through the mounting hole. It may be necessary to thread the screw through the spacer hole. Change spacers as necessary to get the chain as close to centered in the guide as possible with minimal to no rubbing on the inner guide wing. The thinnest 0.25mm spacer can be added to any spacer for very fine tuning. It is best for the chain to be slightly closer to the inner side of the guide if possible.
Loosen the M3 screw at the rear of the chain guide and flex the guide wings around the chain. Do not flex the arms more than necessary. The material is hygroscopic and will be highly flexible in high humidity but becomes stiffer and more brittle when extremely dry.
Slide the M5 T nut up the guide arm and put the guide in the channel for the nut. The nub of the spacer will hold the M5 nut in place while you thread the M5 screw into the T nut. Thread the M5 screw all the way in until it fully compresses the guide and spacer to the guide arm. Back the M5 bolt off until the guide will slide up and down the mount arm.
Slide the guide down the arm until it hits the chain. Flex the wings of the guide around the chain again if necessary. Snug the M5 screw until the guide will move but stay in place when you let go. Turn the cranks until a roller of the chain is in line with the front of the guide. Slide the guide up until there is just barely a gap like shown in the picture. Torque the M5 screw to 4Nm.
Install the M3 screw in the rear of the chain guide. Tighten until the gap between the wings is closed and slightly snug (0.1Nm)
Turn your cranks clockwise and shift through all speeds. Listen and look for any rubbing. Adjust spacer sizing as necessary. On full suspension bikes the smallest cogs may allow the chain to touch the rear catch of the guide. This is normal as the guide was designed for the sag of rear suspension. There may be slight rubbing in the highest or lowest speeds depending on your setup. This should reduce or eliminate with riding. The guide is designed to the most extreme chain angles that guarantee the chain will seat correctly.
If installing a chain catch look at the catch mounting holes to make sure your chain ring will allow access to a pair on the same bolt circle diameter. If not you will need to remove your cranks but follow the remaining steps to determine spacing.
Slide the chain catch between the Rock Bottom and chainring while pressing it against the rock bottom. Check the spacing of the chain in between the path of the catch and wing.
As shown in the picture the chain is too close to the outer wing. Add the correct width spacer to align the chain in the catch without rubbing
Press the round nub of the spacer into the hole at the bottom of the catch while keeping the mounting hole and slot aligned with the catch base.
Slide the catch back into position and secure with the M4 countersunk screw placed through the mounting hole pivot. Snug the screw so that the catch will rotate but stay in place when released.
Shift to the biggest cassette cog and rotate the chain catch so that it is just slightly below the chain with no contact. Install the M4 low profile screw into the radial slot hole and torque both screws to 1Nm.
Turn the cranks clockwise and shift through all the speeds. Look and listen for rubbing. Change shim thickness as necessary.
Shift your bike into the smallest cassette cog.
Remove the chain tensioner M4 axle screw.
Pivot the tensioner cover clockwise out of the way. It may be necessary to loosen the M3 pivot screw slightly to allow motion. Remove the idler and caps.
Insert the M4 countersunk screw into the chain catch base pivot hole.
Install the chain tensioner into the reward M4 mounting point. Tighten until snug. Install the M4 low profile screw into the radial slot mounting hole and tighten until snug.
Install the labyrinth caps onto the idler wheel with flat sides out. The cap with the larger pocket should be installed on the bike side of the idler. Apply medium strength thread locker such as Loctite 243 to the tip of the M4 axle screw and keep the screw within reach. While holding the caps on, push the chain up using the idler wheel. Insert the pocket of the inner idler cap onto the brass heat stake stud while continuing to hold the rest of the idler. The stud will keep the idler in place while you rotate the tensioner cover back into place.
Rotate the tensioner cover until the M4 hole is aligned with the idler. Push the M4 screw through the holes of the tensioner cover and idler assembly. Tighten until slightly snug.
Rotate the tensioner assembly to the desired tension level. We recommend as little tension as possible (even no contact with the idler. Lower tension will increase the life of the idler bearing. The Rock Bottom is designed to keep your chain on with the guide and catch, so the tensioner is just another layer of chain movement reduction.
While holding the tensioner at the desired angle, tighten the M4 low profile screw and torque to a maximum of 1Nm. Torque the M4 countersunk screw at the pivot to 1Nm as well. If you do not have a 3mm ball end hex key it will be necessary to rotate the tensioner cover out of the way by removing the M4 idler axle screw.
Turn your cranks forward and shift through all the speeds. While pedaling torque the M4 axle screw to no more than 1Nm while making sure the pressure does not seize the idler. If the idler stops spinning back the M4 axle screw out until the idler is free to rotate.
Check the tensioner idler often for freedom of rotation and inspect axle screw toque. We recommend inspection before and after each ride.
Congratulations! You now have what we believe is the best protection against damage and chain dropping. We hope the install wasn’t too brutal. If you have fitment or install issues please contact support@brutalengineering.com. We want our products to deliver beyond expectation and any information you can give us allows us to design even better products in the future.