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Yamaha Trim Cylinder Rebuild Procedure
Department: Hydraulic Repair | Level: Advanced | Est Cost: $100
The hydraulic trim system is the most common failure point on saltwater outboards. When seals fail, water displaces the hydraulic fluid, leading to internal corrosion. If this condition is ignored, the aluminum housing will corrode beyond repair, necessitating a full unit replacement costing exceeding $2,500. This procedure details the rebuilding of the Trim Cylinders (the two smaller rams) using Marine Tech precision tooling.
CRITICAL WARNING: Do not use a punch and hammer to remove trim caps. The caps are made of anodized aluminum. Impact force will deform the pin holes and fuse the threads to the housing, rendering the unit non repairable. You must use a pin wrench.
Section 1: Required Tooling and Parts
Success in this procedure is determined by the ability to apply high torque to the end caps without slippage. The following equipment is mandatory.
Essential Service Tools
- Trim Cylinder Wrench (AMT0306): This 32mm wrench fits the trim caps on most Yamaha F115 through F350 units. It features hardened steel pins that will not shear under load.
- Tilt Cylinder Wrench (AMT0309): Required if you are also rebuilding the single large center Tilt cylinder.
- Breaker Bar: A 1/2 inch drive bar is recommended to break the initial corrosion bond.
- Manual Release Valve Tool: A large flat head driver to open the relief valve.
- Snap Ring Pliers: For disassembly of the internal cap components.
- Pick Set: For O Ring removal.
Consumables
- Seal Kit: OEM or aftermarket kit matching your specific Showa unit.
- ATF or Marine Hydraulic Fluid: Dexron III is the standard specification for Yamaha hydraulics.
- Marine Grease: For thread lubrication during reassembly.
Section 2: Preparation and Safety
Hydraulic systems operate under extreme pressure. Failure to relieve pressure prior to disassembly can result in injury.
1. Engage Service Locks
Tilt the engine to the full UP position. Deploy the mechanical service locks (safety legs) located on the engine bracket. Lower the engine until the weight rests firmly on the locks.
2. Relieve System Pressure
Locate the Manual Release Screw on the side of the bracket (access through the hole in the side of the transom plate). Turn the screw counterclockwise three full turns. This opens the internal valves, allowing fluid to flow freely between reservoirs.
Tip: If the manual release screw is seized, do not force it with a small screwdriver. The head will strip. Use a large impact driver bit that fills the entire slot.
Section 3: Disassembly Protocol
3. End Cap Removal
Insert the pins of the AMT0306 Wrench into the trim cap holes. Apply steady counterclockwise pressure using a breaker bar. Do not use sudden impact. Once the threads break free, spin the cap off by hand.
Pull the Piston Sub Assembly upward to remove it from the cylinder housing.
4. Component Inspection
Clean the piston rod with solvent. Inspect the chrome surface for pitting. Run your fingernail over the shaft.
- Smooth Chrome: Serviceable. Proceed with seal replacement.
- Pitting or Rust: The rod is scrap. New seals will be destroyed by the rough surface within hours. You must replace the piston rod.
5. Housing Evacuation
Use a fluid extractor to remove the old oil from the cylinder bore. Inspect the bottom of the bore for metal shavings. Aluminum flakes indicate the piston has been grinding against the cylinder wall, requiring a full unit replacement.
Section 4: Seal Replacement
Disassemble the End Cap to replace the three critical barriers: the Dust Wiper, the O Ring, and the Internal Rod Seal.
6. Cap Rebuild
Secure the cap in a soft jaw vise. Use snap ring pliers to remove the retaining ring. Remove the old seals using a pick, taking extreme care not to scratch the aluminum seal grooves.
Installation: Coat new seals in fresh hydraulic fluid. Press the new Dust Wiper into the top position. Install the Rod Seal in the center groove. Install the external O Ring on the cap threads.
Section 5: Reassembly and Bleeding
7. Charging the Cylinders
Before installing the pistons, pour fresh ATF into the cylinder bore. Fill until the fluid level reaches the bottom thread of the housing.
8. Piston Installation
Lubricate the piston seal and the cap O Ring with fluid. Insert the Piston Sub Assembly into the bore. Press down firmly until the cap threads engage.
Tighten the cap using the pin wrench. Torque to factory specification (typically 120 foot pounds, or until fully seated flush with the housing).
Watch the O Ring: As you tighten the cap, ensure the O Ring does not pinch or bulge out. If resistance increases suddenly, back off and check seal alignment.
9. Air Purge Procedure (Bleeding)
Air trapped in the system causes "spongy" operation and noise. To bleed the system:
- Tighten the Manual Release Screw.
- Press the trim switch UP. Run the motor until the rams extend fully and the sound changes (the pump enters bypass mode).
- Check the fluid reservoir level. Top off if necessary.
- Loosen the Manual Release Screw.
- Allow the engine to drift down slowly by gravity. Do not force it down.
- Repeat this cycle 3 times.
10. Reservoir Cap Warning
The plastic reservoir fill cap has very fine threads. Do not overtighten. Hand tight is sufficient. Overtightening will crack the reservoir, creating a water entry point.
Conclusion
By replacing the seals before saltwater intrusion occurs, you have extended the life of your trim unit by years. Regular inspection of the dust wipers (the top seal on the ram) is recommended every 100 hours.
For additional hydraulic tools and support, visit the Marine Tech Hydraulics Department.
