Sierra Upper Unit Seal Kit 18-2648, Replaces Mercury Marine 26-32511A1, MerCruiser Alpha One

The Sierra 18-2648 Upper Unit Seal Kit supplies the seals needed to rebuild the upper gear housing on MerCruiser stern drive units. It is designed for the 888, 228, 250, and 260 stern drives as well as the MR Alpha One, Alpha One SS, and Alpha One Gen II drive families, covering multiple serial number ranges across those unit generations. The kit is used during a gear housing rebuild or seal replacement service, restoring the upper unit's ability to hold gear lubricant and keep water out of the drive, which protects the gears and bearings from corrosion and premature wear. This kit is a direct equivalent for Mercury Marine part number 26-32511A1, so it installs in place of the original equipment seal set without modification. As a kit, it bundles the seal components needed for the upper unit service in a single part number, saving the buyer from having to source individual seals separately. Because MerCruiser drive designs changed across model years and serial number breakpoints, always confirm the drive model and serial number against the fitment list below before ordering to be sure the 18-2648 kit matches the unit being serviced.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-2648
• Product Type: Upper Unit Seal Kit
• Included Components: Upper Unit Seal Kit
• UPC: 030999755810
• Weight: 0.22 pounds
• OEM Cross Reference: 26-32511A1

Fitment

• 888 / 228 / 250 / 260, 1977-1982, serial number 4782330 to 6225576
• R, 1983, serial number 6225577 and up
• MR Alpha One, 1984-1990, serial number 6225577 to D469858
• MR Alpha One (CR), 1984-1990, serial number 6225577 to D469858
• Alpha One SS, 1986-1989, serial number A545004 and up
• Alpha One Gen II, 1991-1995, serial number D469859 to F679999
• Alpha One Gen II (CR), 1991-1995, serial number D469859 to F679999
• Alpha One Gen II, 1996-1997, serial number F680000 to K999999
• Alpha One Gen II (CR), 1996-2010, serial number F680000 and up

Replaces (OEM)

• Mercury Marine 26-32511A1

Frequently Asked Questions

What does the Sierra 18-2648 Upper Unit Seal Kit fit? The 18-2648 kit fits MerCruiser 888, 228, 250, and 260 stern drives from 1977-1982, plus the MR Alpha One, Alpha One SS, and Alpha One Gen II drive families across specific serial number ranges, from serial number 4782330 up through the F680000-and-up range depending on the model.

Is the 18-2648 kit the same as Mercury Marine 26-32511A1? Yes, Sierra part number 18-2648 is a direct equivalent to Mercury Marine part number 26-32511A1 and installs in its place.

How much does the 18-2648 Upper Unit Seal Kit weigh? The Sierra 18-2648 Upper Unit Seal Kit weighs 0.22 pounds.

What is included in the 18-2648 kit? The kit includes the seal set needed to service the upper gear housing on the applicable MerCruiser drive, packaged as a single Upper Unit Seal Kit under part number 18-2648.

Will 18-2648 fit an Alpha One SS drive? Yes, the 18-2648 kit fits the Alpha One SS drive for the 1986-1989 model years, serial number A545004 and up.

Does the serial number matter when ordering this seal kit? Yes, because MerCruiser drive designs changed across production, the 18-2648 kit applies to specific serial number ranges within each model, so the drive's serial number should be checked against the fitment list to confirm this is the correct kit.

Is 18-2648 for the upper or lower gear housing? The 18-2648 kit is specifically for the upper unit (upper gear housing), not the lower unit.

Does 18-2648 fit the Alpha One Gen II drive? Yes, the 18-2648 kit covers the Alpha One Gen II drive for 1991-1995 and 1996-1997, as well as the Alpha One Gen II (CR) variant for 1991-1995 and 1996-2010.

Is the Sierra 18-2648 a genuine OEM part or an aftermarket replacement? Sierra 18-2648 is an aftermarket seal kit manufactured as a direct replacement for the Mercury Marine OEM part 26-32511A1.

Can this kit be used on the 888, 228, 250, or 260 stern drive models? Yes, part number 18-2648 is listed for the 888, 228, 250, and 260 stern drives for the 1977-1982 model years, serial number range 4782330 to 6225576.