Sierra 18-2771 Bellows Kit, OEM 3854270 Replacement for OMC Cobra Sterndrive Without Cone Clutch

The Sierra 18-2771 Bellows Kit is a complete replacement bellows and gasket package built for OMC Cobra sterndrives without a cone clutch. Bellows are one of the most critical wear items on a sterndrive: they seal the connection between the transom and the outdrive, keeping water out of the boat and out of the drive's u-joint and exhaust passages while allowing the drive to steer and tilt. Over time the rubber in these bellows hardens and cracks from heat, fuel, and UV exposure, which is the leading cause of water intrusion and corrosion damage in sterndrive boats.

This kit bundles the components needed to reseal the drive in one job rather than sourcing each bellows and gasket separately: an exhaust bellows, a u-joint bellows, and an outdrive gasket set. Sierra manufactures its bellows and gasket products to meet or exceed the original equipment they replace, so the fit and sealing performance match what the OMC Cobra drive was designed around. Installing all three components together at the same time is the standard practice for this job, since they wear out on a similar schedule and the outdrive typically has to come off the boat to access any one of them.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-2771
• Product Type: Bellows Kit
• Fitment: OMC Cobra without cone clutch
• Kit Contents: Exhaust Bellows, U-Joint Bellows, Outdrive Gasket Set
• OEM Cross Reference: 3854270
• Weight: 3.69 pounds
• Product Dimensions: 8.75 x 9.75 x 8 inches
• UPC: 808282100896

Fitment

• OMC Cobra sterndrive without cone clutch

Replaces (OEM)

• 3854270

Frequently Asked Questions

What does the Sierra 18-2771 Bellows Kit fit? This kit is built for the OMC Cobra sterndrive without a cone clutch. It is not a universal bellows kit, so confirm your drive is the non-cone-clutch Cobra configuration before ordering.

What OEM part number does this kit replace? The Sierra 18-2771 kit replaces OEM number 3854270 on the OMC Cobra sterndrive without cone clutch.

What is included in the 18-2771 bellows kit? The kit contains an exhaust bellows, a u-joint bellows, and an outdrive gasket set, giving you the parts needed to reseal the drive in one job.

How much does the 18-2771 Bellows Kit weigh? The complete kit weighs 3.69 pounds.

What are the dimensions of the packaged kit? The Sierra 18-2771 Bellows Kit measures 8.75 x 9.75 x 8 inches as packaged.

Why do sterndrive bellows need to be replaced? Bellows are rubber seals that harden and crack over time from heat and UV exposure. Once cracked, they let water into the boat and drive, so the exhaust and u-joint bellows in the 18-2771 kit are typically replaced on a regular maintenance interval.

Should the exhaust bellows, u-joint bellows, and gasket set be replaced together? Yes, and that is why they are bundled in the Sierra 18-2771 kit. Since the outdrive has to be removed to access these parts, replacing all three at once avoids doing the job twice.

Is the Sierra 18-2771 kit genuine OEM or aftermarket? It is a Sierra-manufactured aftermarket kit engineered to meet or exceed the OEM part it replaces, OEM number 3854270, rather than an original OMC-branded part.

Does this kit work on a Cobra sterndrive with a cone clutch? No, the 18-2771 kit is specified for the OMC Cobra without a cone clutch. A cone-clutch equipped Cobra uses a different bellows kit.

Is installation of this bellows kit a DIY job? Installing the 18-2771 kit requires removing the outdrive from the transom to access the bellows and gasket set, which is a more involved job best suited to someone comfortable with sterndrive service or a marine technician.