Mercruiser 87399A3 Trim Cylinder Overhaul Kit – Fits Alpha One Gen II (s/n 2A480243 & Below)

$274.99

Shipping calculated at checkout.

Worry-free returns

You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).

You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).

If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.

Delivery and Shipping

Free standard shipping on all orders under 1 KG

If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

This is a complete Mercruiser 87399A3 Trim Cylinder Overhaul Kit designed for Mercruiser Alpha One Gen II stern drives with serial numbers 2A480243 and below. It contains all the necessary seals, balls, and pistons to rebuild a single trim cylinder and restore its proper function.

This kit provides a direct interchange for Sierra 18-2429 and GLM 700-26580, offering a reliable alternative to restore your trim system's performance.

Engineered as a direct replacement for a precise fit.
Specifically designed for trim cylinders on Alpha One Gen II stern drives.
Includes all essential components for a standard overhaul.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Brand	Part Number
Mercruiser	87399A3
Sierra	18-2429
GLM	700-26580

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For Mercury Marine engines, ensure your model and serial number range match the specifications listed to guarantee compatibility.

Brand	Model	Application	Years	OEM Part No.	Notes
Mercruiser	Alpha One Gen II	Stern Drive	Up to s/n 2A480243	87399A3	Special order item

Technical Specs

Product Type: Trim Cylinder Overhaul Kit
Installation: Direct OEM replacement
Product Dimensions: 6.0" L x 6.0" W x 5.0" H
Other Technical Attributes: For trim cylinders on Alpha One Gen II stern drives

What’s in the Box

3 x Detent Ball (160084)
1 x Screw (N/A)
1 x Spacer (N/A)
3 x Spring (N/A)
1 x Ball - Chrome (N/A)
1 x Eyelet (N/A)
1 x Spring (N/A)
1 x Spring Pin (N/A)
1 x Floating Piston (N/A)
1 x Spring Seat (N/A)
3 x Valve Seat (N/A)
1 x Shock Piston (N/A)

Installation Notes

Disconnect the battery and ensure the stern drive is properly supported before beginning work.
Remove the target trim cylinder from the stern drive assembly. Note the routing of hydraulic lines.
Carefully disassemble the cylinder on a clean workbench, laying out all parts in order.
Inspect the cylinder bore, piston, and rod for scoring, pitting, or other damage.
Replace all seals, O-rings, and other components using the new parts from the overhaul kit.
Lubricate new seals and components with a suitable marine hydraulic fluid or grease during assembly.
Reassemble the cylinder, making sure to torque all fasteners to the manufacturer's specifications.
Reinstall the overhauled cylinder onto the stern drive.
Reconnect hydraulic lines and bleed the trim system according to the official service manual.
Cycle the trim system multiple times to ensure smooth operation and check for any leaks before use.

Troubleshooting & FAQ

How do I know if this kit fits my Alpha One Gen II?

This kit is specifically for Mercruiser Alpha One Gen II stern drives with a serial number of 2A480243 or below. It is critical to check your drive's serial number plate before ordering to ensure compatibility.

What are the signs my trim cylinder needs an overhaul?

Common symptoms include hydraulic fluid leaking from the cylinder end caps, a slow or weak trim response, or the stern drive "drifting" down from its trimmed position over time.

Does this kit rebuild one or two cylinders?

This kit contains all the necessary components to overhaul one single trim cylinder. If you need to service both the port and starboard cylinders, you must purchase two kits.

Are special tools required for this installation?

While many steps can be completed with standard mechanic's tools, a special pin spanner wrench is often required to safely remove the cylinder's end cap. Consulting a service manual for your specific drive model is highly recommended.

OEM vs. Aftermarket?

This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.

Shipping speed & cost

We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.

Warranty & returns

Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.

Safety & Important Info

Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
This is an aftermarket replacement, not an OEM component.
Professional installation is recommended for safety and performance.

About Sea Sierra

Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.

Payment & Security

Payment methods

Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.