878408A1 Power Trim & Tilt O-Ring Repair Kit for Mercury V6 135-300HP | JLM Marine

Power Trim & Tilt O-Ring Repair Kit for Mercury V6 135-300HP

This premium Power Trim & Tilt O-Ring Repair Kit is engineered for Mercury and Mariner V6 outboard motors ranging from 135HP to 300HP (1998 and newer). It ensures reliable hydraulic sealing and prevents fluid leaks in your power trim cylinder, restoring smooth tilt and trim operation.

This kit directly replaces OEM part numbers 878408A1, 878408A 1, 25-878408A1, and 8M0142341. Upgraded with high-grade Viton and Urethane seals, it provides a superior, long-lasting solution compared to standard factory seals that often degrade over time.

• Comprehensive O-Ring kit for power trim and tilt cylinder rebuilds
• Fits Mercury V6 135-300HP, Verado 4-Cyl, and Gen 3 engines (1998 & UP)
• Manufactured with premium Viton and High-Grade Urethane for maximum durability

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket sources.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here's a guide to help you identify your engine's serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

This repair kit includes all necessary O-rings and seals to rebuild your power trim cylinder (Note: Contains seals for the cylinders only, not the entire assembly):

• 26x Various O-Rings (Viton / Urethane)
• 1x Trilobe Pin (OEM 821539)
• 2x Poppet Assembly
• 1x Valve Assembly
• 1x Tilt Wiper Seal & 2x Wiper Seals
• Manifold Screws & Filter Caps

Installation Guide

1. Ensure the outboard motor is securely supported and the trim system is depressurized before beginning work.
2. Remove the power trim and tilt assembly from the engine bracket following your Mercury service manual.
3. Carefully disassemble the trim cylinders. Take note of the orientation of all internal components.
4. Remove old seals, O-rings, and wipers. Clean all cylinder walls and grooves thoroughly with a lint-free cloth and appropriate solvent.
5. Inspect the cylinder walls and rods for scoring, pitting, or corrosion. Replace hard parts if necessary.
6. Install the new Viton and Urethane seals from the kit. Lightly lubricate all new O-rings with premium power trim fluid before installation to prevent tearing.
7. Reassemble the cylinders and reinstall the trim unit onto the outboard.
8. Fill the reservoir with the recommended Mercury Power Trim fluid, bleed the system of air by cycling it up and down several times, and check for leaks.

Troubleshooting & FAQ

Q: How do I confirm this kit fits my Mercury engine?
A: Verify your engine is a V6 (135-250HP) from 1998 or newer, a 2.5L/3.0L DFI/Optimax, or a 4-Cylinder Verado (135-200HP). You can also cross-reference OEM part numbers 878408A1 or 25-878408A1.

Q: Why are my original trim seals leaking?
A: Factory OEM seals from certain eras are known to soften and degrade over 5-10 years of use in harsh marine environments. This kit uses upgraded Viton and Urethane materials designed to resist degradation and outlast the originals.

Q: Does this kit rebuild the entire trim and tilt unit?
A: No, this specific kit (878408A1) contains the O-rings and seals for the cylinders only. It does not contain all the O-rings for the entire valve body/manifold assembly.

Q: Is this an OEM or aftermarket part?
A: This listing is a premium aftermarket replacement part. We build to exceed OEM specifications using superior-grade Viton and Urethane materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.