This is the classic, venerable Bushnell™ Eccentric that’s enabled proper chain tension on tandems and oddball singlespeed rigs since the 90’s. You’re in good company. (U.S. Patent No. 8,070,633)

WARNING: Cycling can be dangerous. Bicycle products should be installed and serviced by a professional mechanic. Never modify your bicycle or accessories. Read and follow all product instructions and warnings including information on the manufacturer’s website. Inspect your bicycle before every ride. Always wear a helmet.

WARNING: Read these instructions completely before beginning installation of this product. If you lack the knowledge or tools to perform installation, please have your local professional bicycle mechanic perform the installation. Improper installation can result in loss of control or damage to the bicycle and/or serious injury.


The Eccentric Bottom Bracket is compatible with frames equipped with bottom bracket shells measuring 54–57mm in diameter and accepts standard English threaded bottom bracket cups.

The Eccentric Bottom Bracket (EBB) may be used on bicycles designed for ASTM use condition 3. This is a set of conditions for operation of a bicycle that includes Condition 1 (paved surfaces) and Condition 2 (gravel and unpaved roads and trails) as well as rough trails, rough unpaved roads, and rough terrain and unimproved trails that require technical skills. Jumps and drops are intended to be less than 61cm (24").




4mm hex wrench

Torque wrench w/ 4mm hex bit

Spanner wrench or bottom bracket installation tools


1. Prep the EBB and frame.

    a. Remove the EBB retaining rings using an awl or similar tool (fig. 1) to disassemble the EBB.

Figure 1

    b. Clean and liberally grease all the contact surfaces: the outside of the wedge nuts, wedge bolt threads, the inside of the wings, and the inside of the frame’s bottom bracket shell (figs. 2–4).


Figure 2                                                                                       Figure 3

  Figure 4

    c. Reassemble. Before reassembly perform a thorough visual inspection of the frame and bottom bracket area. Check for cracking or other signs of fatigue or damage. If any frame part shows signs of damage or fatigue, consult your dealer or replace the frame before riding the bicycle.

    WARNING: Riding a cracked or damaged frame may result in an accident and serious injury. Never ride a cracked or damaged frame.NOTE: To ensure proper access to the wedge bolt in tandem applications, the 4mm wedge bolt head should face the drive side of the bike frame. For solo frames, the wedge bolt head should face the non-drive side (fig. 5). In both cases, the reverse, left-hand bottom bracket threads should face the right, drive side of the frame.

2. Install the EBB into the frame.

    a. Insert the EBB into the frame’s bottom bracket shell and position it to be centered from side to side.

    b. Rotate to the EBB to position the wedge bolt at 3 o’clock when viewed from the drive side, 9 o’clock from the non-drive side (fig. 5).

   c. Use a 4mm hex wrench to cinch the EBB into place (fig. 6).


  Figure 5                                                                             Figure 6

3. Install the bottom bracket and assemble the drivetrain.

    a. Grease the EBB threads as well as the bottom bracket cups (fig. 7).

Figure 7

    b. Install the bottom bracket cups per the manufacturer’s instructions (fig. 8).

    c. Assemble the cranks, chain, and rear cassette/cogs (fig. 9).


  Figure 8                                                                             Figure 9

4. Adjust chain tension.

    a. Loosen the 4mm wedge bolt. NOTE: The bolt must be loosened until both wedges are free. Otherwise the EBB will not rotate.

   b. With the chain installed, rotate the EBB forward using a spanner wrench or bottom bracket tool (fig. 10).

   c. Position the EBB so that the chain is tight, then back it off just slightly.

   d. Tighten the 4mm wedge bolt to 8.5–10Nm (fig. 11).


  Figure 10                                                                             Figure 11

   e. If your chain is too loose or too tight, adjust the EBB fore and aft as necessary. NOTE: Side-to-side adjustment of the EBB to optimize chainline is permitted ONLY if the EBB does not extend outside the frame’s bottom bracket shell.


Check the EBB wedge bolt and chain tension before every ride. Adjust and tighten as necessary.

WARNING: Improper installation of bolts may lead to product failure, causing serious injury. Do not exceed specified torque values. Periodically inspect bolts and retighten if required.


If you and your shop think your Problem Solvers product is worthy of a warranty inspection, please return the product to the original place of purchase, accompanied by a sales receipt.