Mounting Plate to Drive Shaft Housing Gasket – Fits Mercury/Mariner 20 & 200 HP Outboards (Replaces 27-39402)

$14.00

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 aftermarket Mounting Plate to Drive Shaft Housing Gasket is engineered to create a reliable seal for vintage Mercury and Mariner 20 & 200 HP outboard motors. It prevents leaks between the mounting plate and the driveshaft housing, ensuring the integrity of your engine's internal components.

This part is a direct replacement for Sierra 18-0334, Mercury 27-39402, and Quicksilver 27-39402, offering a precise fit and OEM-level performance.

Installation involves replacing the seal between the mounting plate and drive shaft housing.
Constructed from durable paper/fiber composite to match original specifications.
Designed for use with vintage Mercury/Mariner outboard engines.

Part Number Matrix

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

Brand	Part Number
Mercury Marine	27-39402
Quicksilver	27-39402
Sierra	18-0334

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This gasket is designed for specific serial number ranges of Mercury and Mariner outboards. Please verify your engine's serial number against this list to ensure correct fitment.

Brand	Model	Rated HP	OEM Part No.	Notes
Mercury	200	200	27-39402	Serial numbers: 1866496-2296266
Mercury	200	200	27-39402	Serial numbers: 2296267-2827676
Mercury	200	200	27-39402	Serial numbers: 2827677-3226957
Mercury	200	200	27-39402	Serial numbers: 3226958-3537530
Mercury	200	200	27-39402	Serial numbers: 3537531-4709592
Mercury	200, 20	200, 20	27-39402	Serial numbers: 4709593 & Up
Mercury	200	200	27-39402	Serial numbers: 7012358-7098522
Mercury	200, 20	200, 20	27-39402	Serial numbers: 7098523 & Up
Mercury	200	200	27-39402	Serial numbers: 8006265-8045198
Mercury	200, 20	200, 20	27-39402	Serial numbers: 8045199 & Up
Mercury	200	200	27-39402	Serial numbers: 9016254-9157229
Mercury	200, 20	200, 20	27-39402	Serial numbers: 9157230 & Up

Technical Specs

Product Type: Mounting Plate to Drive Shaft Housing Gasket
Installation: Replaces seal between mounting plate and drive shaft housing
Material: Paper/Fiber Composite
Dimensions: 10.88 × 8.0 × 1.13 inches
Weight: 0.06 lb (0.027 kg)
OEM Part Number: 27-39402 (Mercury)
Aftermarket Part Number: 18-0334 (Sierra)
Color: Brown/Tan
Application: Vintage Mercury/Mariner outboard engines

What’s in the Box

1 x Gasket (27-39402)

Installation Notes

Disconnect the battery and all power to the engine.
If necessary, drain gearcase lube or other relevant fluids.
Carefully disassemble engine components to access the connection between the mounting plate and driveshaft housing.
Remove all bolts and separate the two components.
Take off the old gasket and thoroughly clean any residue from both mating surfaces.
Position the new gasket, ensuring it aligns with all bolt holes and channels.
Reassemble the housing and plate, tightening bolts to the manufacturer's torque specifications.
Refill any fluids drained earlier and check thoroughly for leaks before operation.

Troubleshooting & FAQ

How do I confirm this gasket fits my specific engine?

The most reliable method is to match your engine's serial number to the ranges listed in the Engine & Model Compatibility table. Since these are vintage models, year data is not always available, making the serial number the key identifier.

What are the signs of a failed drive shaft housing gasket?

Common symptoms include water intrusion into the gearcase lube (milky or cloudy oil), visible oil or water leaks around the housing seam, or overheating if water passages are compromised.

Can I reuse my old gasket or use a liquid sealant instead?

No. Gaskets are designed for a single use; they compress to create a seal and will not work correctly if reused. We do not recommend using liquid sealant as a substitute unless specified by the original engine manufacturer, as it can block oil or water passages.

Is this part different from the original OEM gasket?

This aftermarket gasket is manufactured to meet or exceed original equipment specifications for fit, material, and function. It is a direct replacement designed for durability and a perfect seal, just like the original.

How often should this gasket be replaced?

This gasket does not have a set replacement interval. It should be replaced anytime the components it seals are separated for service or if a leak is detected.

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.