Sierra 18-1143 Tapered Roller Bearing, Replaces 31-42647A1, for Mercury Outboard Gearcase

The Sierra 18-1143 Tapered Roller Bearing is a precision alloy steel bearing built for the gearcase of Mercury outboard motors. It is machined to original-equipment tolerances so it seats correctly on the pinion and drive shaft assemblies it is designed to support, carrying both radial and axial loads inside the lower unit. Alloy steel construction gives the bearing the hardness and load capacity needed to handle the constant thrust and rotational stress generated inside a marine gearcase, where heat, vibration, and water-adjacent operating conditions place extra demand on components.

This bearing is a direct cross-reference for the OEM number listed below, so it installs as a like-for-like replacement without modification. It ships as a single bearing, ready to be pressed into place using standard bearing installation tools and packed with the gearcase lubricant already used in the unit. Because tapered roller bearings wear gradually with use, replacing a worn 18-1143 during a gearcase rebuild or seal service helps restore proper shaft alignment and reduce play in the lower unit.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-1143
• Category: Mercury Outboard Gearcase Bearing
• Material: Alloy Steel
• Bearing Type: Tapered Roller Bearing
• Compatible Lubricant: Grease
• Item Dimensions: 0.39 x 0.39 x 0.39 inches
• Weight: 0.55 pounds
• UPC: 030999752277
• Country of Origin: United States

Fitment

• Mercury outboard gearcase assemblies using the 18-1143 tapered roller bearing position

Replaces (OEM)

• 31-42647A1

Frequently Asked Questions

What does the Sierra 18-1143 tapered roller bearing fit? The 18-1143 is designed for the gearcase of Mercury outboard motors, where it supports the pinion and drive shaft assembly against radial and axial loads.

Is the 18-1143 a direct OEM replacement? Yes, Sierra 18-1143 is a direct cross-reference for OEM number 31-42647A1 and installs in place of that original bearing without modification.

What size is the Sierra 18-1143 bearing? The 18-1143 tapered roller bearing measures 0.39 x 0.39 x 0.39 inches and weighs 0.55 pounds.

What material is the 18-1143 bearing made from? It is made from alloy steel, giving the 18-1143 the hardness needed to handle the thrust and rotational loads inside a marine gearcase.

What lubricant should be used with the 18-1143 bearing? The Sierra 18-1143 is compatible with standard gearcase grease lubricant used during installation and ongoing service.

Is this a genuine Sierra part or an aftermarket copy? The 18-1143 is a genuine Sierra International part, manufactured to meet or exceed the specifications of the original equipment bearing it replaces.

What comes in the box with the 18-1143? Each order includes one Sierra 18-1143 tapered roller bearing; no additional hardware or seals are included.

How is the 18-1143 bearing installed? The 18-1143 is pressed into the gearcase housing using standard bearing installation tools, typically during a gearcase rebuild or seal replacement.

Why does a tapered roller bearing like the 18-1143 need replacing? Tapered roller bearings wear gradually with use, and a worn 18-1143 can allow shaft play or misalignment inside the lower unit, making replacement necessary during a rebuild.

Does the Sierra 18-1143 come with a warranty? The Sierra 18-1143 tapered roller bearing carries Sierra's limited warranty covering manufacturing defects.