FAW Locking Ring: The 7 Essential MSUs for a Perfect, Silent, and Secure Cab

Welcome to this critical component analysis of the FAW Locking Ring, Positioning Pin, and Weatherstrip assembly (Assembly 691). This is the complete, 7-type, “cab-side” counterpart system for the ‘FAW Front Door’ (Assembly 683) on the FAW Jiefang CA4251P66K24T1A3E5 6×4 tractor. This assembly is the “logic” of the cab’s B-pillar, providing the three functions for a perfect door seal:

1. Latching Logic: The FAW Locking Ring (MSU 4) provides the hardened steel “striker” for the door’s ‘Lock Body’ (689) to grab.

2. Alignment Logic: The ‘Positioning Pin Seat’ (MSU 2) provides the “guide” to ensure the door aligns perfectly, preventing sag and rattles.

3. Sealing Logic: The ‘Weatherstrip’ MSUs (1 & 7) provide the “gasket” that the door compresses against to block wind and water.

This in-depth guide is essential for collision repair specialists and parts managers. We will deconstruct the entire FAW Locking Ring assembly into its 7 distinct Minimum Serviceable Unit (MSU) types. We will analyze the “compression latch” logic of the main ‘Locking Ring’ (the primary MSU), the “anti-sag” logic of the ‘Positioning Pin Seat’, the “dual-bulb” logic of the ‘Weatherstrips’, and the critical, specialized fasteners that provide a safe, vibration-proof installation.

Core 1: The “Latching & Compression” Logic (MSUs 4, 5, 6) (The “Longer” Module)

This group of MSUs is the “security” core of the assembly. It is the “passive” side of the ‘Door Lock Mechanism’ (Assembly 689).

1. MSU 4: ‘Locking ring assy’ (6105125-A01)

This is the primary MSU and the namesake of the FAW Locking Ring assembly. It is the heavy-duty “striker” or “latch pin” that is mounted on the cab’s B-pillar. Its “logic” is to be the immovable “anchor” that the door’s ‘Lock Body’ (Assembly 689) rotary latch “captures.”

Construction & Wear Logic: This is not a simple loop of steel. It is forged or cast from high-tensile, hardened steel to resist wear from millions of open/close cycles. It is also coated (e.g., zinc-plated) to be 100% corrosion-proof. The “logic” of its design is critical: it is the “camming” surface.

Compression Logic: When the ‘Lock Body’ (689) engages this FAW Locking Ring, it “pulls” the door *past* its neutral point. This “pulling” action is the “logic” that creates “compression.” It actively squeezes the ‘Front Door Outer Weatherstrip’ (MSU 1) tight, creating the “bank vault” seal that blocks wind noise (NVH) and water. A worn or misaligned FAW Locking Ring is the #1 cause of a “rattly” or “leaky” door.

2. MSUs 5 & 6: The “Flush-Mount” Fastener Logic

This is the specialized hardware for the FAW Locking Ring. The system uses four (4) ‘Cross recessed countersunk head screws’ (Q2540825) and four (4) ‘Taper pin lock washers’ (Q41408).

Countersunk “Logic” (MSU 5): The “logic” of using a “countersunk” (flush-mount) screw is critical. The ‘Lock Body’ (689) on the door *must* pass over this area to engage the FAW Locking Ring. A protruding hex-bolt head would “foul” or “jam” the mechanism. These screws sit perfectly flush, creating a smooth “skid plate” for the latch.

Taper Lock “Logic” (MSU 6): A countersunk screw cannot use a standard “spring washer.” The “logic” here is the ‘Taper pin lock washer’. This is a specialized “star washer” that is *also* cone-shaped. Its “teeth” are designed to “bite” into the countersunk bevel of the screw (MSU 5) *and* the metal of the cab’s B-pillar. This “biting” logic is the “anti-vibration” feature, providing the essential locking tension to prevent this critical safety MSU from *ever* vibrating loose.

Core 2: The “Alignment & NVH” Logic (MSUs 2 & 3)

This group of MSUs provides the “alignment” logic for the door, which is essential for the FAW Locking Ring to function.

MSU 2: ‘…Positioning Pin Seat’ (6101547-A01 / 6101548-A01): This is the “female” receiver. The ‘Front Door’ (683) has a “male” guide pin. This “Pin Seat” (MSU 2) is the polymer-lined “hole” that the pin slides into *before* the latch engages.

Alignment Logic: Its “logic” is to “guide” the heavy, sagging door into *perfect* vertical alignment. This ensures the door’s ‘Lock Body’ (689) hits the FAW Locking Ring (MSU 4) *perfectly* every time, preventing “missed latches.”

NVH Logic: The polymer lining of this MSU also acts as a “buffer.” It provides a tight, “anti-rattle” fit for the door pin, which prevents the door from vibrating, shaking, and “clunking” against the B-pillar on rough roads.

MSU 3: ‘Hexagon flange bolt’ (Q1840612F6): These four (4) bolts are the “structural logic” for the Pin Seat. They are high-tensile, flanged bolts (with a built-in washer) that securely anchor this critical alignment MSU to the cab’s frame.

Core 3: The “Weather & Acoustic” Logic (MSUs 1 & 7)

This final group of MSUs is the “sealing logic” of the assembly. They provide the “gasket” that the FAW Locking Ring system compresses.

MSU 1: ‘…Outer Weatherstrip Assy’ (6107015-A01 / 6107020-A01): This is the *primary* cab seal. It is the large, EPDM rubber “U-channel” that is mounted on the “pinch weld” of the *cab body* (the B-pillar).

Its “logic” is to be a “dual-bulb” (hollow-core) seal. This design is a “logic” choice for superior NVH. The hollow “bulb” compresses easily, providing a “soft” door close, while also creating a “double-wall” barrier that is exceptionally effective at blocking wind noise and water.

MSU 7: ‘Front door upper weatherstrip’ (6107031-A01-C00): This is the *secondary* seal. The “logic” of this separate piece is that the “top” of the door frame has a different shape and “logic.” This MSU is not just a “bulb” seal; it is often a “drip rail” seal, designed to actively *channel* water away from the ‘Side Window’ (634).

Both of these MSUs are critical wear items. When they crack or “compression set” (flatten) with age, the FAW Locking Ring (MSU 4) can no longer create a tight seal, leading to wind noise and water leaks.

FAW Locking Ring & Seal Assembly Parts List

The following table provides the complete, detailed breakdown of all 7 component types identified in the FAW Locking Ring, Pin Seat, and Seal assembly for the FAW CA4251P66K24T1A3E5 tractor.

Specifications

The specifications for the FAW Locking Ring assembly are defined by its function as the cab-side “counterpart” system for latching, alignment, and sealing.