1-12551139-0 1125511390 OEM Intake Valve 46 mm Head Diameter 128 mm Overall Length for ISUZU 4BD1 6BD1 Engine Inlet Valve

The Intake Valve with OEM numbers 1-12551139-0 and 1125511390 is a verified direct-fit replacement for ISUZU FSR / FTR / NRR / NPR medium-duty trucks equipped with 4BD1 / 6BD1 / 4BG1 / 6BG1 / 4BC2 / 4BA1 / 4BB1 / 6BB1 diesel engines. This intake valve is a critical component of the cylinder head assembly, responsible for controlling the admission of air into the combustion chamber during the intake stroke.

The intake valve opens at a precise moment during the engine cycle to allow fresh air to enter the combustion chamber, then closes at the exact time to seal the chamber for compression and combustion. This precise timing is crucial for maintaining proper engine breathing, enhancing power production, and ensuring efficient combustion.

ISUZU genuine intake valves are manufactured from high-grade heat-resistant alloy steel to withstand combustion temperatures and continuous high-speed opening and closing cycles. The valve features a hardened stem tip and a precision-ground head manufactured to exacting dimensional tolerances.

The 4BD1 is a 3.9L inline-four direct-injection diesel engine and the 6BD1 is a 5.8L inline-six variant, both widely used in ISUZU FSR/FTR/NRR trucks from 1985 to 1999. The 4BG1 and 6BG1 are 4.3L and 6.5L engines respectively, used in ISUZU NPR/FSR trucks and Hitachi excavators.

Replace the intake valve when any of these symptoms appear:

• Engine misfiring or rough running — a burned or warped valve cannot seal properly, causing compression loss and misfiring.
• Loss of power and reduced fuel economy — a leaking intake valve reduces engine efficiency and power output.
• Excessive exhaust smoke or unusual engine noise — a damaged valve allows combustion gases to escape improperly.
• Valve clearance out of specification — valve clearance changes indicate valve face or seat wear.
• Visible burning, cracking, or warping on the valve head — indicates the valve has exceeded its service life and must be replaced.
• Hard starting or rough idle — poor sealing from a worn valve causes low compression and difficult starting.

Primary ISUZU Applications:

Non-ISUZU Applications (Same Engine Platform):

Mitsubishi Fuso Reference (Same Engine Platform):

Installation Guidelines — Reference ISUZU 4BD1/6BD1 Workshop Manual

1. Preparation: Remove the cylinder head from the engine. Clean the cylinder head thoroughly. Remove all old valves, springs, and seals.
2. Inspection: Inspect the valve guides for wear. Measure the valve guide bore and compare to specification. Inspect the valve seats for pitting or erosion. Replace or recondition as necessary.
3. Valve Installation: Lubricate the new valve stem with clean engine oil. Insert the valve into the guide. Install the valve spring, retainer, and keepers.
4. Valve Clearance Adjustment: Set the cold valve clearance to specification. Adjust the rocker arm screw until the feeler gauge slides with slight drag.
5. Cylinder Head Installation: Install the cylinder head with a new gasket. Torque the head bolts in the specified sequence and stages.
6. Final Check: Rotate the engine by hand to verify smooth valve operation. Check for any binding or interference.
7. Engine Start: Start the engine and check for abnormal noise or exhaust smoke. Verify proper valve operation.

Recommended Torque Values:

Maintenance Schedule:

• Every 1,200 operating hours: Adjust valve clearance. Inspect valve train for abnormal noise.
• Every 40,000–50,000 km: Inspect valve guides and seats. Check valve stem wear.
• When engine performance degrades: Test compression and inspect valves immediately.
• At engine overhaul: Always replace valves, guides, and springs as a complete set.

• Standard Packaging: Anti-rust oil + VCI film + neutral carton.
• Custom Packaging: Neutral box, color box, or customer-branded packaging.
• Suitable For: Engine repair shops, ISUZU parts distributors, fleet maintenance centers, construction equipment repair shops.
• Supply Capacity: Stable batch supply with batch-level quality reports available.
• MOQ: No minimum quantity requirement.