Cloyes S851 Engine Timing Crankshaft Sprocket - Inner

Cloyes S851 Timing Crankshaft Sprocket

The Cloyes S851 is a specific-fit engine timing crankshaft sprocket for select GM vehicles with an inner timing application. It features a helical tooth form for quieter operation and a precision-machined bore for accurate fit during engine repair or rebuild work.

Built from metal and CAD designed for consistent dimensions, this timing sprocket is used in timing system service where reliable chain engagement and stable crankshaft timing are required. Fits 2000-2017 Buick, Chevrolet, GMC, Pontiac, Saturn, and Oldsmobile applications listed below.

• Specific-fit engine timing crankshaft sprocket for inner timing applications
• 42-tooth design with 0.12 in tooth width
• Precision-machined 1.11 in inside diameter for true fit
• Helical tooth form for quieter timing system operation
• Metal construction with gray finish
• Keyway notch included for proper indexing
• Cross-reference: 90537301

Detailed Product Overview

Cloyes S851 is an engine timing crankshaft sprocket used in the timing chain system on a wide range of GM compact and midsize vehicles, including Chevrolet Malibu, Chevrolet Cobalt, Buick Regal, and GMC Terrain. The sprocket works with the timing chain, tensioners, and guides to maintain correct camshaft and crankshaft synchronization. Cloyes manufactures this part with advanced materials and tests it for function and durability to support engine rebuilds and routine timing service. The part number S851 is also referenced as 90537301 for the same application.

Common Repair Uses

• Worn or damaged crankshaft sprocket teeth
• Timing chain noise caused by sprocket wear
• Incorrect chain tracking in the inner timing system
• Engine timing service on Chevrolet Malibu, Chevrolet Cobalt, and Buick Regal
• Timing system refresh during rebuilds on GM 2.0L/2.2L/2.4L-era applications

Installation Notes

Verify application by year, make, model, and inner position before installation. Inspect the timing chain, tensioner(s), and guide(s) during service, since worn components can affect sprocket life and chain tension. Confirm the keyway notch alignment and bore fit during assembly, and follow the vehicle service procedure for timing marks and torque specifications.

Quality Assurance

Cloyes designs this sprocket using CAD-based engineering and validates it through functional and durability testing. The S851 is manufactured for dependable timing system service in engine rebuilds and replacement repairs.