Crank Left Arm with Diamond Hole, 170mm Aluminium Alloy Bicycle Crank Arm Left Replacement for Mountain Bike Road Bike (Black)

Crank Left Arm with Diamond Hole, 170mm Aluminium Alloy Bicycle Crank Arm Left Replacement for Mountain Bike Road Bike (Black)170mm Aluminum Alloy Left Crank Arm (Diamond Hole) Key Features Precision Diamond Hole Interface: Features a square taper interface oriented at a 45 degree "Diamond" angle relative to the crank arm, ensuring compatibility with specific square taper bottom brackets. High Strength Aluminum Alloy: Forged from premium 6061 aluminum alloy to provide high fatigue resistance and durability while remaining lightweight for improved pedaling efficiency.

170mm Aluminum Alloy Left Crank Arm (Diamond Hole)

Key Features

• Precision Diamond Hole Interface: Features a square taper interface oriented at a 45-degree "Diamond" angle relative to the crank arm, ensuring compatibility with specific square-taper bottom brackets.
• High-Strength Aluminum Alloy: Forged from premium 6061 aluminum alloy to provide high fatigue resistance and durability while remaining lightweight for improved pedaling efficiency.
• Standard 170mm Length: The most common crank arm length, providing an optimal balance between leverage for climbing and ground clearance to prevent pedal strikes.
• Universal Pedal Threading: Features standard 9/16-inch threading, making it compatible with almost all mountain, road, and indoor exercise bike pedals.
• Corrosion-Resistant Finish: Treated with a deep black anodized coating that protects the metal from oxidation, road salt, and moisture.

Replaces / Cross-Reference Part Numbers

• 170mm Left Crank Arm (Diamond Pattern)
• Standard Square Taper Replacement Arm
• Diamond-Hole MTB/Road Crank Arm
• (Note: Not compatible with "Square" hole orientations where the flats are parallel to the arm).

Compatibility & Fitment

This crank arm is a specific replacement part. Before purchasing, you must verify the hole orientation of your original arm:

• Hole Orientation: This is a Diamond Hole. If your current crank arm hole looks like a square (sides parallel to the arm), this will not fit.
• Bottom Bracket: Designed for standard Square Taper (JIS) bottom bracket spindles.
• Bicycle Types: Mountain Bikes (MTB), Road Bikes, Fixed Gear (Fixies), and many Indoor Spin/Exercise bikes.
• Position: This is the Left Side (Non-Drive Side) arm only.

When to Replace

• Rounded-Out Hole: If the crank arm was ridden while loose, the square hole becomes "rounded," causing the arm to wobble or fall off the spindle.
• Stripped Pedal Threads: The internal threads where the pedal attaches are cross-threaded or flattened, making it impossible to secure the pedal.
• Visible Cracks: Stress fractures appearing near the spindle interface or the pedal eyelet, often caused by high-impact jumps or metal fatigue.
• Bent Arm: The arm is visibly warped from a crash or a heavy pedal strike, causing an uneven pedaling motion that can lead to knee pain.

Installation Tips

• Verify Orientation Twice: Hold your old crank arm and the new one side-by-side. Ensure the square holes are oriented in the same "Diamond" direction. If they are different, your pedals will be 45 degrees out of sync.
• Clean the Spindle: Before installing, use a rag to wipe away all old grease and metal shavings from the bottom bracket spindle.
• Grease the Threads: Apply a small amount of bicycle grease to the pedal threads, but keep the square taper spindle clean and dry (or apply a very thin film of oil) to ensure a solid friction fit.
• Tighten to Spec: Use an 8mm hex wrench or 14mm socket to tighten the crank bolt firmly (typically 35–45 Nm). A loose bolt is the #1 cause of rounded-out crank holes.
• Retighten After First Ride: Check the tightness of the crank bolt after your first 10–20 miles. The aluminum "sets" onto the steel spindle and often requires a final snugging.