How to Change a Mercruiser Front Seal

Mercruiser marine engines employ an impeller that circulates coolant when the engine is running. The impeller mounts on the end of the camshaft that passes through a seal in the timing cover. Front seals can wear and leak in time. When you notice coolant leaking at the front of the engine, it’s time to change the seal. In most cases, the engine must be pulled and mounted on a stand to correctly change the front seal. The job requires mechanical aptitude, engine tools and a seal kit you obtain from a marine service center based on the size of the Mercruiser engine.

Things You'll Need

  • Front seal kit
  • Oil drain pan
  • Standard-gauge engine tools
  • 5-gallon bucket
  • Chisel or steel putty knife
  • Wood blocks
  • Screwdriver
  • Light machine oil
  • Large socket
  • Hammer
  • Deep socket
  • RTV gasket sealant
  • Coolant
  • Engine oil
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Instructions

  1. Seal Removal

    • 1

      Position an oil drain pan under the engine. Remove the drain plug from the oil pan, and drain the oil.

    • 2

      Position a 5-gallon bucket under the timing cover at the front of the engine. Remove the brass drain plug at the underside of the cover, and drain the engine coolant into the bucket. Disconnect and remove the front coolant hose at the upper side of the engine.

    • 3

      Loosen and remove the screws where the front of the oil pan attaches to the bottom of the timing cover.

    • 4

      Loosen and remove the screws from the cover plate at the upper face of the timing cover to access the impeller pump. Grip the outer rim of the impeller with one hand as you remove the bolt that secures it to the end of the camshaft. Pull the impeller off the end of the camshaft by hand.

    • 5

      Remove the timing cover bolts. Pry the timing cover away from the face of the engine block with a chisel or steel putty knife to unseat the gasket from the block. Pull the cover straight away from the block to release two rubber dowels that attach to the inside face of the cover and fit into ports on the face of the block.

    • 6

      Place the timing cover face down on wood blocks or a wooden workbench. Position another wood block across the rim of the cover. Use the block as a fulcrum as you pry the rubber dowels out of circular seats on the inside face of the cover with pliers.

    • 7

      Place a small wood block against the edge of the circular seat that holds the front seal at the inside of the cover. Use the block as a fulcrum as you pry the front seal out with a screwdriver.

    • 8

      Remove the timing-cover gasket and any residue from the rim of the cover with the chisel or putty knife.

    Seal Installation

    • 9

      Apply light machine oil in the seats on the timing cover where the front seal and rubber dowels were removed.

    • 10

      Position the front seal from the kit atop the seat on the timing cover with the metallic ring facing up. Center the closed end of a large socket on the ring. Hold the socket with one hand as you tap the open end with a hammer to fit the seal into the seat.

    • 11

      Insert the metallic cup at the end of each rubber dowel from the kit into a seat where the old dowels were removed. Select a deep socket that slides tightly over the upper end of the dowels. Grip the socket with one hand as you tap it with the hammer to seat each dowel.

    • 12

      Apply a uniform bead of RTV gasket sealant on the rim of the cover. Align the holes in the new gasket from the kit with the bolt holes on the cover, and press the gasket onto the rim by hand.

    Reassembly

    • 13

      Coat the end of the camshaft at the front of the engine with light machine oil. Squirt machine oil into both dowel ports on the face of the engine block.

    • 14

      Position the timing cover at the face of the engine block so the seal aligns with the end of the camshaft and the ends of the rubber dowels align with the dowel ports. Push the cover straight onto the face of the block by hand until it stops. At this point, the rim of the cover is not against the face of the block, which is correct.

    • 15

      Seat the timing cover against the face of the engine block by tapping the rim at several places with a wood block and the hammer. Secure the cover in place with the original bolts.

    • 16

      Reattach the impeller onto the end of the camshaft with the original bolt. Reattach the cover plate with the original screws. Repeat the initial steps in reverse to complete the job. Fill the cooling system with coolant. Fill the engine with oil.