Sierra 18-21752-1 Engine Coupler, White, Replaces 3858437, Fits 4.3L 5.0L 5.7L (1986-1998)

The Sierra 18-21752-1 is a white marine engine coupler that connects the engine flywheel to the drive unit, transmitting engine power to the outdrive on inboard/outdrive setups. It is built to meet or exceed the specification of the original equipment part it replaces, and Sierra manufactures it to the same fit, form, and function standard used by OEM engine manufacturers and boat builders. This coupler is a direct cross-reference replacement for four OEM part numbers, so it can be ordered under any of those numbers and installed as a like-for-like swap without modification.

The coupler is engineered for GM-based marine engines commonly found in stern drive applications, with confirmed fitment across 4.3L, 5.0L, and 5.7L engine platforms spanning the 1986 through 1998 model years, with specific coverage varying by engine size. Its metal, alloy steel construction is designed to withstand the vibration, torque, and harsh marine operating environment these drivetrain components see in regular service. Because it is a direct OEM cross-reference part rather than a universal fit, boat owners and marine technicians can use it to restore original power transmission between the engine and drive unit during a coupler replacement or drivetrain rebuild.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-21752-1
• Product Type: Engine Coupler
• Color: White
• Material: Metal (alloy steel)
• Weight: 6.45 pounds
• Package Dimensions: 16.764 x 15.748 x 16.256 centimeters (L x H x W)
• UPC: 808282226855
• Warranty: Limited warranty
• OEM Cross-Reference Numbers: 3858437, 984290, 986120, 3853917

Fitment

• 4.3L engines (1986-1998)
• 5.0L engines (1986-1988, 1998)
• 5.7L engines (1986-1992, 1994, 1996-1998)

Replaces (OEM)

• 3858437
• 984290
• 986120
• 3853917

Frequently Asked Questions

What does the Sierra 18-21752-1 engine coupler fit? The Sierra 18-21752-1 fits 4.3L engines (1986-1998), 5.0L engines (1986-1988 and 1998), and 5.7L engines (1986-1992, 1994, and 1996-1998).

Which OEM part numbers does the 18-21752-1 replace? It is a direct cross-reference for OEM numbers 3858437, 984290, 986120, and 3853917, so any of those part numbers can be used to identify the correct replacement.

How much does this engine coupler weigh? The Sierra 18-21752-1 engine coupler weighs 6.45 pounds.

What color is the Sierra 18-21752-1 coupler? This coupler is white.

What material is the coupler made from? It is made of metal, specifically alloy steel construction, built to hold up under marine drivetrain loads and vibration.

Is the 18-21752-1 a genuine Sierra part or aftermarket? The 18-21752-1 is a genuine Sierra marine part manufactured to meet or exceed the specification of the original equipment coupler it replaces.

Will this coupler fit both 5.0L and 5.7L engines the same way? Yes, one 18-21752-1 coupler covers 4.3L (1986-1998), 5.0L (1986-1988, 1998), and 5.7L (1986-1992, 1994, 1996-1998) engines, since fitment is by engine platform rather than a separate part per engine size.

What is included when I order part number 18-21752-1? Ordering Sierra 18-21752-1 includes one marine engine coupler.

Does the Sierra 18-21752-1 differ from the Sierra 18-21753 coupler? Yes, 18-21753 is a separate Sierra coupler part number with its own OEM cross-reference and its own fitment, so buyers should confirm which part number matches their engine before ordering.

What is the package size of the Sierra 18-21752-1? The Sierra 18-21752-1 ships in packaging measuring 16.764 x 15.748 x 16.256 centimeters (L x H x W).

Is there a warranty on the Sierra 18-21752-1 engine coupler? The 18-21752-1 is covered by a limited warranty.

Can I cross-reference the 18-21752-1 using an old OMC or Volvo part number? Yes, if your old coupler is stamped 3858437, 984290, 986120, or 3853917, the Sierra 18-21752-1 is the correct direct replacement.