Harley-Davidson X440T Head Cover Gasket HDH12391ACJ000S | Genuine Rocker Cover Gasket

Harley-Davidson X440T Head Cover Gasket – HDH12391ACJ000S

Replace a leaking, hardened, flattened or damaged cylinder-head / rocker-cover gasket with the correct genuine Harley-Davidson X440T gasket. Part number HDH12391ACJ000S is identified in the supplied X440T parts list as GASKET HEAD COVER. In buyer language, this is commonly searched as a head cover gasket, rocker cover gasket, valve cover gasket, or tappet cover gasket.

This listing is built around both the official catalogue wording and the terms owners, mechanics and workshops actually use when searching online: Harley X440T head cover gasket, X440T rocker cover gasket, X440T valve cover gasket, Harley X440T engine top cover gasket, and the exact OEM reference HDH12391ACJ000S.

The head-cover gasket seals the joint between the engine's cylinder head and the removable top cover. Its job is to help keep engine oil contained inside the valve / rocker area while preventing oil seepage around the cover joint. A worn or damaged gasket can lead to visible oil sweating or leakage around the top of the engine.

Product Identity

• Brand: Harley-Davidson
• Part Number: HDH12391ACJ000S
• Official Catalogue Description: GASKET HEAD COVER
• Common Search Names: Head Cover Gasket / Rocker Cover Gasket / Valve Cover Gasket
• Application Area: Cylinder-head top cover / valve-train cover sealing
• Quantity: 1 piece

Confirmed Compatibility

• Harley-Davidson X440T – January 2026 / R4AA

Fitment note: the supplied X440T catalogue confirms this SKU for the January 2026 X440T application. Do not assume compatibility with another X440 generation only because the gasket looks similar; use the exact part number whenever possible.

What This Gasket Does

• Seals the joint between the head cover and cylinder head
• Helps prevent engine-oil seepage from the valve / rocker area
• Maintains the intended sealed top-end environment
• Provides the correct shape and sealing profile for the specified application

When Should It Be Replaced?

Replacement is commonly considered when:

• Oil is visible around the head-cover joint
• The gasket has hardened, flattened, cracked or torn
• The head cover has been removed for inspection or top-end service and the old gasket is no longer serviceable
• There is oil staining or seepage from the upper engine area
• A previous repair used sealant or an incorrect gasket and the joint is leaking

Important – Gasket Only

HDH12391ACJ000S is the head-cover gasket only. It is not the complete cylinder-head cover and it is not a full engine gasket kit.

Do not confuse this part with:

• Breather plate gasket
• Breather plate
• Cylinder-head gasket
• Complete engine gasket kit
• Head-cover bolts or washers
• Oil seals or O-rings used elsewhere in the engine

Why Exact Part-Number Matching Matters

• Engine gaskets can look very similar but differ in profile and sealing points
• An incorrect gasket can cause oil leakage or poor cover seating
• Exact SKU matching reduces wrong-part returns
• Correct genuine fitment avoids trimming or modifying a universal gasket

What’s in the Box

• 1 x Genuine Harley-Davidson X440T Head Cover Gasket
• Part number: HDH12391ACJ000S

Installation Notes

• Clean the mating surfaces before installation
• Do not damage or pinch the new gasket while positioning the cover
• Inspect the head cover and mating surface for distortion or old gasket residue
• Tighten cover fasteners evenly and to the correct workshop specification
• Avoid excessive sealant unless the service procedure specifically requires it
• After installation, inspect for oil seepage once the engine has been run

Return Prevention Note

Please match HDH12391ACJ000S and confirm you require the GASKET HEAD COVER. If you need the head gasket, breather gasket, complete cover or another engine seal, those are separate parts.

FAQs

1. What is HDH12391ACJ000S?
It is the genuine head cover gasket listed for the Harley-Davidson X440T.

2. Is this also called a rocker cover gasket?
Yes. Buyers and mechanics may refer to this type of part as a rocker cover gasket or valve cover gasket, while the catalogue description is GASKET HEAD COVER.

3. Which motorcycle is confirmed?
The supplied parts list confirms Harley-Davidson X440T – January 2026 / R4AA.

4. Is this the cylinder-head gasket?
No. The cylinder-head gasket seals a different joint in the engine. This part seals the removable head / rocker cover.

5. Can this help fix oil seepage from the top of the engine?
If the seepage is coming from the head-cover joint and the existing gasket is worn or damaged, replacing the correct gasket is part of the repair. The mating surfaces and cover condition should also be inspected.

6. Should the gasket be reused after removing the head cover?
If the old gasket is hardened, damaged, compressed, torn or no longer sealing correctly, replacement is the safer choice.

Harley X440T head cover gasket, X440T rocker cover gasket, X440T valve cover gasket, Harley X440T tappet cover gasket, X440T engine top cover gasket, GASKET HEAD COVER, HDH12391ACJ000S.