The Comprehensive Guide: FAW Cylinder Head Assembly for the CA4251P66K24T1A3E5 Tractor

This comprehensive technical guide provides an exhaustive analysis of the FAW Cylinder Head Assembly (Part No. 1003011-81D), a core component of the engine for the FAW Jiefang CA4251P66K24T1A3E5 6×4 diesel semi-trailer tractor.

The FAW Cylinder Head Assembly is arguably the most complex and critical static component in the powertrain. It serves as the “lungs” of the engine, managing all airflow, fuel injection, and combustion, while also routing high-pressure oil for lubrication and coolant for thermal management.

This exploded-view analysis is designed for professional engine rebuilders, machine shops, and service technicians. We deconstruct the entire FAW Cylinder Head Assembly into its smallest serviceable units, from the main casting and valvetrain components to the individual seals, plugs, and dowel pins that are essential for a successful engine overhaul.

Core Component: The Cylinder Head Casting (1003011-81D)

The foundation of the entire FAW Cylinder Head Assembly is the main casting (Part No. 1003011-81D). This single component is a masterpiece of foundry work, typically made from a high-strength, high-temperature cast iron or a specialized aluminum alloy. It is responsible for sealing the top of the engine’s cylinders, forming the upper half of the combustion chamber.

Its complex internal structure is a marvel. It contains intricate, cast-in-place “water jackets” that allow engine coolant to circulate mere millimeters away from the combustion chambers and exhaust ports, absorbing and carrying away the immense heat of combustion. Failure to control this heat would lead to component warping, detonation, and catastrophic engine failure.

Simultaneously, it features a separate network of drilled passages that carry high-pressure oil from the engine block up to the valvetrain, lubricating the camshafts, rocker arms, and valve stems. The precision of this casting is paramount. The “deck” surface—the bottom face that meets the engine block—must be perfectly flat to ensure a complete seal with the head gasket, containing the millions of PSI generated during the power stroke.

Valvetrain Infrastructure: Seats and Guides

This FAW Cylinder Head Assembly is a four-valve-per-cylinder design, which is a hallmark of modern, efficient diesel engines. This is evidenced by the parts list quantities: for a six-cylinder engine, we see 12 ‘Intake Valve Seats’ (1003012-81D) and 12 ‘Exhaust Valve Seats’ (1003013-81D). This 2:2 split per cylinder (2 intake, 2 exhaust) allows for superior airflow, or “breathing,” resulting in more complete combustion and higher power output.

The valve seats are not part of the casting itself. They are separate rings made of an extremely hard, specialized steel alloy. The “softer” head casting is machined, and these hardened seats are chilled (often with liquid nitrogen) and pressed into place, where they expand to form an interference fit. They serve two functions: to provide a durable, heat-resistant surface for the valve to seal against, and to transfer the valve’s heat into the water-cooled head. Exhaust valve seats, in particular, are made from exotic alloys to withstand the superheated exhaust gases.

To support the 24 valves (12 intake, 12 exhaust), the parts list specifies 24 ‘Valve Guides’ (1003014-81D). These are bronze or iron sleeves that are also pressed into the head. The valve stem passes through this guide, which holds the valve in perfect alignment as it opens and closes thousands of times per minute. The guide also serves as a critical heat-transfer path, drawing heat from the valve stem and conducting it into the head casting.

These components—seats and guides—are the primary “serviceable units” for an engine machine shop. Over time, the seats wear from the constant pounding of the valves, and the guides wear, leading to oil consumption and poor valve sealing. A “valve job” on a FAW Cylinder Head Assembly involves machining or replacing these specific parts to restore the head to a like-new condition.

Fuel Injector Integration Components

In a modern direct-injection diesel, the fuel injector tip sits directly in the combustion chamber. In the FAW Cylinder Head Assembly, this is accomplished by passing the injector through the water jacket. To make this possible, six ‘Injector Copper Sleeves’ (1003016-81D) are used, one for each cylinder.

This copper sleeve is a thin-walled tube that is pressed and sealed into the head, creating a dry “tunnel” through the coolant. It serves three critical functions: it seals the coolant *out*, it seals the high-pressure combustion gases *in* (at the bottom), and its copper construction provides excellent heat transfer, using the engine coolant to cool the high-performance injector.

The parts list also shows six ‘O-rings’ (1003018-53D). These are most likely the seals used at the top of the injector sleeve or on the injector itself, preventing oil from the valvetrain (above) or coolant (from a potential sleeve leak) from seeping down into the fuel system.

Camshaft Bearing Caps and Alignment

This FAW Cylinder Head Assembly is an overhead cam (OHC) design, meaning the camshaft(s) are housed within the head. The head casting forms the lower half of the camshaft bearing. The ‘Camshaft Upper Bearing Cap Assembly’ bolts on top to complete the bearing circle.

The parts list is very specific: six units of ‘Camshaft Upper Bearing Cap Assembly – 1 to 6’ (1003070-81D) and one unit of ‘Camshaft Upper Bearing Cap Assembly – 7th’ (1003075-81D). For a six-cylinder engine, this indicates seven bearing journals. The six “standard” caps are for the main journals, while the one “7th” cap is different. This is typically the thrust bearing, which has special flanges to control the camshaft’s axial (front-to-back) movement.

These caps are “line-bored” at the factory, meaning they are machined while bolted to the head. As a result, they are a matched set and are *not* interchangeable. To ensure perfect re-assembly, 14 ‘Dowel Pins’ (1003079-81D) are used to lock the caps in their exact position before the bolts are tightened.

Core Plugs and Gallery Seals

The final items on the list are the seals for the manufacturing passages. The casting process for the complex water jackets leaves several large holes in the side of the FAW Cylinder Head Assembly. These are sealed by the ‘Cup Plugs’ (CQ72222, CQ72226, CQ72248). The parts list calls for 13, 20, and 8 units, respectively, a total of 41 plugs of various sizes, sealing the entire coolant system.

Conversely, the oil galleries, which feed the valvetrain, are drilled with long, straight bits. The ends of these drilled holes must be sealed. This is the job of the two ‘Inner Hex Tapered Screw Plugs’ (Q61903). These are threaded plugs that seal the high-pressure oil system.

FAW Cylinder Head Assembly Parts List

The following table provides the complete, detailed breakdown of all components identified in the ‘Cylinder Head Assembly’ diagram for the FAW CA4251P66K24T1A3E5 tractor.

Technical Specifications and Assembly Context

The specifications for the FAW Cylinder Head Assembly are defined by its complex, multi-functional design for a 6-cylinder, 24-valve engine.