The Honda 12251-Z5T-003 Cylinder Head Gasket (Nippon Leakless) is a genuine OEM replacement designed for GX340 and GX390 horizontal shaft engines, as well as a wide range of Honda generators, two-stage snow blowers, and water pumps. As a factory-sourced component, this gasket is manufactured to Honda's original specifications, ensuring it matches the exact geometry and clamping requirements of the cylinder head it seals. This part covers an extensive fitment range, including EB, EG, EM, EU, and EU-series generators, HS and HSS two-stage snow blowers, and the WT40 water pump — verify your model and serial number against the fitment table before ordering.
Key Features
- Genuine OEM Sealing Integrity — sourced directly from Honda, this Nippon Leakless gasket delivers the correct head-sealing performance for the GX340 and GX390 engine family, with no guesswork on material grade or clamping retention.
- Broad Compatibility — fits GX340 and GX390 horizontal shaft engines powering Honda generators including EB3800, EB4000, EB5000, EB6500, EB7000, EG5000, EG6500, EM3800, EM4000, EM5000, EM6500, EM7000, EU6500, and EU7000 units, HS928, HS1332, HS1336, HSM1336, HSS928, and HSS1332 two-stage snow blowers, and the WT40 water pump.
- Serial Number Verification Recommended — Honda supersedes gasket part numbers at engine serial breaks; confirm your unit's serial number against the fitment table to ensure part number 12251-Z5T-003 is correct for your specific build.
- Direct Head Replacement — this gasket installs in place of the original with no rework to mating surfaces beyond standard preparation, making a head-off service straightforward for experienced technicians.
- Combustion Containment — a failed or compressed-out cylinder head gasket allows combustion gases to escape the chamber, leading to power loss, overheating, and coolant or oil contamination; replacing it with the correct OEM gasket restores full compression and protects the engine from further damage.
The cylinder head gasket forms the critical seal between the cylinder head and the engine block, containing combustion pressure and preventing the mixing of combustion gases, oil, and any coolant passages present in the engine. On air-cooled engines like the GX340 and GX390, maintaining that seal is essential to holding compression and keeping the engine running at full power. When a head gasket fails — through age, overheating, or improper torque — the engine typically loses compression, runs roughly, consumes oil, or develops visible exhaust leaks at the head joint, all of which demand immediate replacement to avoid escalating engine damage.
Part Details
| Part Number | 12251-Z5T-003 |
|---|---|
| Brand | Honda |
| Part Type | Genuine OEM |
| Description | Cylinder Head Gasket (Nippon Leakless) |
Compatibility & Fitment
| Name | Models | Serial Range |
|---|---|---|
| Generator | EB3800, EB4000, EB5000, EB6500, EG5000, EG6500, EM3800, EM4000, EM5000, EM6500 | All |
| Horizontal Shaft Engine | GX340, GX390 | All |
| Inverter Generator | EB7000, EM7000, EU6500, EU7000 | All |
| Two-Stage Snow Blower | HS928, HS1332, HS1336, HSM1336, HSS928, HSS1332 | All |
| Water Pump | WT40 | All |
Verify Before You Order
Fitment is machine-number and revision-specific; always confirm your model and serial number against the fitment list.
Why Buy From DHS Equipment
Every part is verified against the manufacturer's part number before it ships, so what you order is what arrives. We carry parts from leading OEM brands and our own DHS Quality Parts line of professional aftermarket components. Need help finding the right part? Our team is available to confirm compatibility whenever you need it. Orders are processed fast to keep your jobs on track. We don't just sell parts. We keep you jobsite ready.
Questions? Contact our team at [email protected] or 866-611-9369 — DHS Equipment is here to help you maintain peak performance.
