Cylinder Boring; Cylinder Honing; Piston Selection - Mercury MerCruiser Service Manual

Engine Inspection and Assembly
NOTE: If engine block inspection indicates that the block is suitable for continued service, out of round, or tapered cylinders can
be reconditioned by honing or boring and honing.
1. If cylinders have less than 0.127 mm (0.005 in.) wear, they can be reconditioned with a hone and fitted with high limit
standard size pistons. If there is more than 0.127 mm (0.005 in.) wear, bore and hone to fit the smallest oversized piston
that will permit the complete resurfacing of all cylinders.
2. Clean cylinder bores with hot soapy water. Rinse thoroughly. After cleaning, lightly lubricate the cylinder walls with engine
oil and a clean cloth. Wipe off excess oil with a clean dry cloth.

Cylinder Boring

IMPORTANT: Before using any type of boring bar, file the top of the engine block to remove dirt or burrs. This prevents boring
bar tilt (the bored cylinder wall is not at right angles to the crankshaft).
1. File the top of the engine block to smooth any irregular surface and remove any deposits or burrs.
2. Clean the cylinders with warm water and detergent. Rinse thoroughly.
3. Measure the piston to be fitted with a micrometer. Take measurements at the center of the piston skirt and at right angles
to the piston pin.
NOTE: Hone cylinders as outlined under Cylinder Honing and Piston Selection .
4. Bore the cylinder to the same diameter as the piston and hone to provide the specified clearance.
5. Carefully observe equipment manufacturer's instructions.

Cylinder Honing

1. Follow the instructions provided with the cylinder hone kit.
Description
Kent‑Moore cylinder hone tool kit
2. Frequently clean the cylinder bore and check the piston for a correct fit in the cylinder.
3. When finish‑honing a cylinder bore to fit a piston, move hone up and down at a sufficient speed to obtain very fine uniform
surface finish marks in a 30 degree cross hatch pattern. Finish marks should be clean but not sharp, free from embedded
particles, and torn or folded metal.
4. As each piston is fitted to a cylinder, permanently mark each with its corresponding cylinder number.
IMPORTANT: Handle pistons with care and do not attempt to force them into a cylinder until it is honed to the correct size.
5. Thoroughly clean cylinder bores with hot soapy water. Scrub each cylinder with a stiff, synthetic bristle brush, and rinse
thoroughly with hot water. Lightly lubricate the cylinders with light engine oil on a clean cloth, then wipe clean with a clean
dry cloth. Repeat this process several times until the oiled cloth remains clean and free of machining debris. The cylinder
should not be cleaned with kerosene or gasoline. Clean the engine block to remove dirt and debris left by the
reconditioning process.

Piston Selection

1. Check used piston to cylinder bore clearance:
a. Measure the cylinder bore diameter with a telescope gauge 64 mm (2.5 in.) from the top of the cylinder bore.
Page 3B-8
Measuring cylinder bore diameter
© 2016 Mercury Marine
Part Number
30450
90-8M0099748 eng DECEMBER 2015
J5902‑01