How to Overhaul a Mercury Outdrive
When you overhaul a Mercury outdrive, a mechanic isn't always necessary since, in an overhaul, you are little more than a "parts changer," swapping good parts for bad, based on your inspection. Replacement kits for bearings, the water pump, seal kits, the various shafts, bearing assemblies and bearing sets are available from a variety of sources and at a variety of prices. While the water pump and impeller require inspection once a season, the rest is left to the times when you notice a hesitation or when something is plainly inoperable.
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Things You'll Need
- Acetone
- Water pump replacement kit
- Compressor
- Hose
- Air nozzle
- Lower unit lubricant
- Ball bearings
- Tapered roller bearing sets
- Shaft roller bearing support
- Pinion gear
- Drive gear
- Propeller shaft sliding clutch
- Reverse gear side clutch dogs
- Shift spool assembly
- Propeller shaft roller bearing sets
- Seal replacement set
Instructions
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1
Clean all water pump parts with solvent such as acetone, then dry them with compressed air. Inspect the water pump cover and base for cracks and distortion, possibly caused from overheating. Inspect the face plate and water pump insert for grooves and/or rough surfaces. Replace parts as necessary from a water pump replacement kit.
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2
Inspect the impeller side seal surfaces and the ends of the impeller blades for cracks, tears and wear. Check for a glazed or melted appearance, caused by operating without sufficient water. If any question exists install a new impeller if at all possible.
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3
Clean all bearings with solvent, dry them with compressed air from a compressor equipped with a hose and an air nozzle and inspect them carefully. Be sure there is no water in the air line. Direct the air stream through the bearing. Never spin a bearing with compressed air -- this is highly dangerous and can cause the bearing to score from lack of lubrication. After the bearings are clean and dry, lubricate them with lower unit lubricant. Do not lubricate tapered bearing cups until after they have been inspected.
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4
Inspect all ball bearings for roughness, catches and bearing race side wear. Hold the outer race and work the inner bearing race in-and-out, to check for side wear. Determine the condition of the tapered bearing rollers and the inner bearing race by inspecting the bearing cup for pitting, scoring, grooves, uneven wear, embedded particles and discoloration caused from overheating. Replace tapered roller bearings as a set.
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5
Inspect the bearing surface of the shaft roller bearing support. Check the shaft surface for pitting, scoring, grooving, embedded particles, uneven wear and discoloration caused from overheating. The shaft and bearing must be replaced as a set if either is unfit for continued service. Check shaft surfaces at oil seal contact areas, as grooves or wear in that area will allow leakage. Install replacements as needed.
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6
Clean the bearing carrier, pinion gear, drive gear clutch and the propeller shaft with solvent, such as acetone. Dry the cleaned parts with compressed air. Check the pinion gear and the drive gear for abnormal wear. Apply a coating of lightweight oil, like household oil, to the roller bearing. Rotate the bearing and check for cracks or catches.
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7
Inspect the sliding clutch of the propeller shaft. Check the reverse gear side clutch dogs; note that rounded dogs result from poor operating practices such as changing gears "on the fly." Inspect the shift spool assembly for wear. Inspect the propeller shaft roller bearing surfaces for pitting, rust marks, uneven wear, embedded metal particles or signs of overheating caused by lack of adequate lubrication. Replace as necessary.
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8
Inspect the propeller shaft oil seal surface to be sure it is not pitted, grooved or scratched; replace as necessary from the seal set. Inspect the roller bearing contact surface on the propeller shaft for pitting, grooves, scoring, uneven wear, embedded metal particles and discoloration caused from overheating. If evidence of overheating exists and your initial inspection of the water pump revealed no external damage, look for evidence of broken impeller vanes in the water tube.
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Tips & Warnings
Always install new O-rings and oil seals regardless of their appearance.
If anything looks out of place, wrong or broken, compare it to the new part. If it still looks out of place, wrong or broken, replace it.
Disconnect the negative cable of your battery before performing any maintenance work on your outboard motor, to prevent electrical shock or accidental starting. Remove the nut from the negative post with a 5/16-inch box-end wrench. Lift the cable from your battery, move it outside of the battery box and close the lid of the battery box.
If you work on your outdrive when your boat is on its trailer, or your motor is on a storage stand, remove the propeller nut with a wrench and slide the thrust hub, propeller and washers from the propeller shaft. Failure to remove a propeller before operating an outboard out of the water during maintenance or long-term storage is an invitation to a propeller-strike injury, which can maim or kill.
