A Vital Guide: FAW Timing Gear Assembly for the CA4251P66K24T1A3E5 Tractor

Welcome to this vital technical guide on the FAW Timing Gear Assembly, the mechanical “clockwork” that synchronizes the entire engine of the FAW Jiefang CA4251P66K24T1A3E5 6×4 diesel semi-trailer tractor. This system is the non-negotiable heart of engine timing.

Unlike a timing belt or chain, the FAW Timing Gear Assembly is a robust, gear-driven system designed for the extreme torque and high-mileage demands of heavy-duty diesel operation. This assembly connects the crankshaft to the camshaft, fuel injection pump, and air compressor, ensuring every component operates in perfect, permanent synchronization. A failure in the FAW Timing Gear Assembly is catastrophic.

This in-depth guide is an essential resource for professional engine technicians, machine shops, and fleet parts managers. We will deconstruct the entire FAW Timing Gear Assembly into its smallest serviceable units, including every master gear, idler gear, shaft, and thrust plate, to ensure precision diagnostics and assembly.

The Master and Driven Gears of the Assembly

The entire FAW Timing Gear Assembly operates on a master-and-slave principle. The ‘Crankshaft timing gear’ (1005037-81D) is the “master” gear. It is keyed directly to the snout of the crankshaft and is the single source of power for the entire system. Its rotation is the baseline “time” for the engine.

This master gear directly or indirectly drives all other components in the FAW Timing Gear Assembly. The most critical “slave” gear is the ‘Camshaft timing gear’ (1006021-81D). This gear is bolted to the front of the camshaft using the ‘Fastening bolt – camshaft timing gear’ (1006017-53D). It is precisely timed to the crank gear (via idler gears) to ensure the engine’s valves open and close at the correct piston position.

Equally important are the “accessory” drive gears. The ‘Fuel injection pump drive gear’ (1111216-81D) is timed just as precisely, as it drives the high-pressure fuel pump, dictating the exact moment of fuel injection. The ‘Air compressor driven gear’ (1006047-81D) is also driven by this FAW Timing Gear Assembly, providing constant power to the vehicle’s air brake system.

The Idler Gear Train: Transferring Motion

The crank gear and cam gear do not mesh directly; they are too far apart. The space between them is bridged by a series of idler gears. This is the “logic” in the FAW Timing Gear Assembly. These idlers are not just spacers; they are precision-engineered components that ensure the correct rotational direction and gear reduction.

This engine uses a “gear train” of multiple idlers. The parts list calls out several ‘Timing idler gear assembly’ units (1006060-81D and 1006070-81D) and a ‘Timing idler gear (II)’ (1006053-81D). This indicates a multi-gear system to transfer power. One of the most complex is the ‘Timing idler stack-gear assembly’ (1006040-81D). A “stack-gear” is two gears of different diameters machined onto a single hub. This is a common way to provide two different gear reductions or to offset the rotational path from a single shaft.

Each of these gears must spin freely and in a precise location. They are mounted on dedicated ‘Timing idler gear shafts’. The list specifies a ‘Timing idler stack-gear shaft (I)’ (1006051-81D) and a ‘Timing idler gear shaft (III)’ (1006057-81D). These hardened steel shafts are bolted to the engine block, and the idler gears spin on them, typically on a bronze bushing or needle-roller bearing. The proper lubrication and alignment of this idler train are essential for a quiet and reliable FAW Timing Gear Assembly. Any wear in these bushings will cause a “rattling” noise and can lead to gear failure. This entire network of idlers is a core strength of the FAW Timing Gear Assembly.

The axial (front-to-back) position of these helical-cut gears is just as important as their rotation. Helical gears naturally create a “thrust” force. The ‘Timing idler gear (III) thrust plate’ (1006056-81D) is a critical wear item. This hardened steel plate bolts to the front of the idler shaft and provides a low-friction surface for the gear hub to ride against. It prevents the gear from “walking” off its shaft. A worn thrust plate will allow excessive “end-play” in the idler gear, leading to a loud whining noise and potential damage to the entire FAW Timing Gear Assembly.

Critical Fasteners and Locators

A gear-driven system like the FAW Timing Gear Assembly is held together by high-strength, specialized fasteners. The ‘Fastening bolt – camshaft timing gear’ (1006017-53D) is a single, large, high-tensile bolt. It is almost certainly a Torque-to-Yield (TTY) bolt that must be replaced after one use. It provides the immense clamping force needed to lock the cam gear to the camshaft, preventing any slippage that would destroy the engine’s timing. This is one of the most critical bolts in the entire FAW Timing Gear Assembly.

The idler gear shafts are secured by various ‘Inner hex socket head cap screws’ (CQ2181040TF2 and CQ2181070TF2) and ‘Hex flange bolts’ (Q1840840). The use of inner-hex (Allen key) bolts is common where clearance is tight. These TF2-suffixed bolts are likely high-strength (Class 10.9 or 12.9) and may have a factory-applied thread-locking compound. The proper torque on these fasteners prevents the idler shafts from vibrating loose, which would be catastrophic for the FAW Timing Gear Assembly.

Finally, the ‘Dowel pin’ (Q5210616) provides precision. This hardened steel pin is pressed into the engine block and is used to locate one of the idler gear shafts in its one, exact position. This ensures the gear-to-gear “backlash” (the small gap between the teeth) is perfect. Too much backlash causes a rattling noise, while too little (a “tight” mesh) causes a high-pitched whine and rapid wear. This pin ensures the factory-set precision of the FAW Timing Gear Assembly every time it is serviced.

FAW Timing Gear Assembly Parts List

The following table provides the complete, detailed breakdown of all components identified in the ‘Timing Gear Logic Assembly’ diagram for the FAW CA4251P66K24T1A3E5 tractor. A complete overhaul of the FAW Timing Gear Assembly requires meticulous inspection of each of these parts.

Technical Specifications and Assembly Context

The specifications for the FAW Timing Gear Assembly are defined by its function as the master timing system for the engine. The entire FAW Timing Gear Assembly is a high-precision, heavy-duty system.