Gasket, Air Heater – Fits Yanmar Diesel Engines (Replaces 121850-77021)
Gasket, Air Heater – Fits Yanmar Diesel Engines (Replaces 121850-77021) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Free standard shipping on all orders under 1 KG
Gasket, Air Heater – Fits Yanmar Diesel Engines (Replaces 121850-77...
Product Details
This Gasket, Air Heater is a direct replacement part designed for a wide range of Yanmar industrial and marine engines, including the 3TNE, 4TNE, 3TNV, 4TNV, LH, and LY series diesel engines. It ensures a proper seal for the air heater component, which is essential for reliable cold-weather starts.
It serves as a direct replacement for Yanmar part number 121850-77021 and aftermarket equivalents like Maxiforce Y121850-77021 and 104284.
- Engineered for a direct replacement fit.
- Made from environmentally friendly, asbestos-free interface material.
- Precision-manufactured to guarantee exact dimensions and proper sealing.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yanmar | 121850-77021 |
| Maxiforce | Y121850-77021 |
| Maxiforce | 104284 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
Yanmar Marine Engines
| Brand | Model | Stroke | OEM Part No. |
|---|---|---|---|
| Yanmar | 1GM | 4-Stroke | 121850-77021 |
| Yanmar | 1GM10 | 4-Stroke | 121850-77021 |
| Yanmar | 2GM | 4-Stroke | 121850-77021 |
| Yanmar | 2GM20, 2GM20F, 2GM20-YEU, 2GM20F-YEU | 4-Stroke | 121850-77021 |
| Yanmar | 2GMF | 4-Stroke | 121850-77021 |
| Yanmar | 2QM, 2QM15, 2QM20 | 4-Stroke | 121850-77021 |
| Yanmar | 2YM15 | 4-Stroke | 121850-77021 |
| Yanmar | 3GM, 3GM30, 3GM30-YEU, 3GM30F, 3GM30F-YEU | 4-Stroke | 121850-77021 |
| Yanmar | 3GMD, 3GMF | 4-Stroke | 121850-77021 |
| Yanmar | 3HM, 3HM35, 3HM35F, 3HMF | 4-Stroke | 121850-77021 |
| Yanmar | 3JH2, 3JH2-TE, 3JH2BE, 3JH2TBE | 4-Stroke | 121850-77021 |
| Yanmar | 3JH3, 3JH3E | 4-Stroke | 121850-77021 |
| Yanmar | 3JH4E, 3JH5E | 4-Stroke | 121850-77021 |
| Yanmar | 3QM, 3QM30, 3QM30F | 4-Stroke | 121850-77021 |
| Yanmar | 3YM20, 3YM30 | 4-Stroke | 121850-77021 |
| Yanmar | 4BY | 4-Stroke | 121850-77021 |
| Yanmar | 4JH-HTBE, 4JH-TE | 4-Stroke | 121850-77021 |
| Yanmar | 4JH110, 4JH2 | 4-Stroke | 121850-77021 |
| Yanmar | 4JH3-DTE, 4JH3-HTE, 4JH3-TE, 4JH3E | 4-Stroke | 121850-77021 |
| Yanmar | 4JH4-DTE, 4JH45, 4JH4AE, 4JH4E | 4-Stroke | 121850-77021 |
| Yanmar | 4JH57, 4JH5E, 4JH80 | 4-Stroke | 121850-77021 |
| Yanmar | 4LH-DTE, 4LH-STE, 4LH-STZ, 4LH-WST, 4LH-WSTZY | 4-Stroke | 121850-77021 |
| Yanmar | 4LHA-DTP, 4LHA-HTP, 4LHA-STP | 4-Stroke | 121850-77021 |
| Yanmar | 4LV150, 4LV195, 4LV230, 4LV250 | 4-Stroke | 121850-77021 |
| Yanmar | 4YB180 | 4-Stroke | 121850-77021 |
| Yanmar | 6AYAM-ET | 4-Stroke | 121850-77021 |
| Yanmar | 6BY2, 6BY3 | 4-Stroke | 121850-77021 |
| Yanmar | 6LP, 6LPA-STP2 | 4-Stroke | 121850-77021 |
| Yanmar | 6LY2-STE, 6LY2A-STP | 4-Stroke | 121850-77021 |
| Yanmar | 6LY3-ETP, 6LY3-STP, 6LY3-UTP | 4-Stroke | 121850-77021 |
| Yanmar | 6LY400, 6LY440, 6LYA-STP, 6LYA-UTE-STE | 4-Stroke | 121850-77021 |
| Yanmar | 6LY-ST, 6LY-STZY, 6LY-UT, 6LY-UTZY, 6LY-WUT, 6LY-WUTZY, 6LY-WST, 6LY-STM | 4-Stroke | 121850-77021 |
| Yanmar | 8LV-320, 8LV-350, 8LV-370 | 4-Stroke | 121850-77021 |
| Yanmar | SB8, SVE12 | 4-Stroke | 121850-77021 |
| Yanmar | YSB8, YSB12 | 4-Stroke | 121850-77021 |
| Yanmar | YSE8, YSE12 | 4-Stroke | 121850-77021 |
| Yanmar | YSM8, YSM12 | 4-Stroke | 121850-77021 |
Yanmar Industrial Engines
| Brand | Model | Stroke | OEM Part No. |
|---|---|---|---|
| Yanmar | 4TNE94-ACG, 4TNE94-DBK, 4TNE94-DBW, 4TNE94-DBWK | 4-Stroke | 121850-77021 |
| Yanmar | 4TNE94-EIK, 4TNE94-G1A, 4TNE94-HLB, 4TNE94-HYB | 4-Stroke | 121850-77021 |
| Yanmar | 4TNE94-SA, 4TNE94-SF, 4TNE94-SFW, 4TNE94-WI | 4-Stroke | 121850-77021 |
| Yanmar | 4TNE98-AG | 4-Stroke | 121850-77021 |
| Yanmar | 3TNE82A | 4-Stroke | 121850-77021 |
| Yanmar | 3TNE84, 3TNE84T | 4-Stroke | 121850-77021 |
| Yanmar | 3TNE88 Non-Turbo | 4-Stroke | 121850-77021 |
| Yanmar | 3TNV70 Non-Turbo | 4-Stroke | 121850-77021 |
| Yanmar | 3TNV76 Non-Turbo | 4-Stroke | 121850-77021 |
| Yanmar | 3TNV82A | 4-Stroke | 121850-77021 |
| Yanmar | 3TNV84 Non-Turbo | 4-Stroke | 121850-77021 |
| Yanmar | 3TNV88 Non-Turbo, 3TNV88C | 4-Stroke | 121850-77021 |
Komatsu & Other Equipment
| Brand | Model | Engine / Notes | OEM Part No. |
|---|---|---|---|
| Komatsu | 4D94E-1A, 4D94E | Uses Yanmar engine | |
| Clark Equipment | C20D, C25D, C30D Forklift | Yanmar 4TNE94 | 121850-77021 |
| Daewoo | SOLAR 55V Excavator | Yanmar 4TNE94 | 121850-77021 |
| Hyundai | Robex 55-3, Robex 55W, Robex 55W-3 Excavator | Yanmar 4TNE94 | 121850-77021 |
| Komatsu | 500PD-14 Forklift | Yanmar 4TNE94 | 121850-77021 |
| Komatsu | D20P-7, D20A-7-M, D20P-7A-M, D20PL-7-M, D20PLL-7-M, D20Q-7-M Tractors | Yanmar 4TNE94 | 121850-77021 |
| Komatsu | D20S-7-M, D21A-7-M, D21P-7A-M, D21PL-7-M, D21Q-7-M, D21S-7-M Loader | Yanmar 4TNE94 | 121850-77021 |
| Komatsu | FD20, FD20T, FD20T-14, FD25, FD30, FD30T-14, P60-BXD Forklifts | Yanmar 4TNE94 | 121850-77021 |
| Komatsu | WA65-3, WA65PT-3, WA75-3 Loader, FG25T-12 Forklift | Yanmar 4TNE94 | 121850-77021 |
| Landini | TREKKER 60F Tractor, QAS28 Generator | Yanmar 4TNE94 | 121850-77021 |
Technical Specs
- Product Type
- Air Heater Gasket
- Installation
- Direct replacement
- Fuel Type
- Diesel
- Material
- Interface material (environmentally friendly, asbestos-free)
- Dimensions
- 9.0" L x 9.0" W x 0.1" H
- Weight
- 0.045 kg (0.1 lbs)
- Manufacturing
- Manufactured with high technology tools to guarantee exact dimensions and proper fit
- Warranty
- Manufacturer warranty available
What’s in the Box
- 1 x Gasket, Air Heater (Replaces 121850-77021)
Installation Notes
- Ensure the engine is completely cool and disconnect the battery before beginning installation.
- Locate the air heater assembly on the engine's intake manifold.
- Carefully remove any components obstructing access to the air heater.
- Remove the bolts securing the air heater, then remove the unit and the old gasket.
- Thoroughly clean both mating surfaces to remove any old gasket residue, carbon, or debris. A clean surface is crucial for a proper seal.
- Position the new gasket, ensuring all holes align perfectly with the engine block and air heater.
- Reinstall the air heater and tighten the bolts to the manufacturer-specified torque in a crisscross pattern to ensure even pressure.
- Reconnect the battery and start the engine to check for smooth operation and ensure there are no air leaks.
Troubleshooting & FAQ
How do I know if this gasket fits my engine?
This gasket fits a wide variety of Yanmar marine and industrial engines. To confirm fitment, please locate your engine model in the comprehensive "Engine & Model Compatibility" lists on this page. Cross-referencing the OEM part number (121850-77021) is the most reliable method.
What are the signs of a failing air heater gasket?
A faulty gasket can cause several issues, including difficulty starting the engine in cold conditions, rough idling when cold, or visible soot, cracking, or damage around the air heater housing.
What is the purpose of an air heater gasket?
The air heater gasket provides a critical seal for the air heater element in a diesel engine's intake system. This prevents air leaks, ensuring the heater can effectively warm the intake air for smooth, reliable starts in cold temperatures.
Can I reuse my old gasket?
No. Gaskets are single-use components designed to crush and create a seal. Reusing an old gasket will likely result in an improper seal, leading to air leaks and poor engine performance.
Is this gasket different from the original OEM part?
This part is manufactured to meet or exceed OEM specifications using a high-quality, asbestos-free interface material for reliable sealing and durability. It offers comparable performance to the original part at a better value.
What happens if I don't replace a bad gasket?
Ignoring a failed air heater gasket can lead to persistent hard starting in cold weather, increased emissions, and potential strain on your engine's starting system. It can also allow dirt and debris to bypass the air filtration system.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
Payment & Security
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