Mercury Piston Kit Standard – Fits Mercury/Mariner 30-40 HP (Replaces 850026T3, 705-850026T3)

$175.99 $281.00

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Delivery and Shipping

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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 high-quality aftermarket Mercury Piston Kit Standard designed for Mercury and Mariner 30-40 HP 2-stroke outboard engines manufactured between 1998 and 2006. Engineered from a durable hypereutectic aluminum alloy, it ensures reliable performance and engine longevity.

It serves as a direct replacement for several OEM part numbers, including Mercury 850026T3, 705-850026T3, 705-850026A3, and 39-821695A4.

Engineered for specific Mercury/Mariner outboard models.
Constructed from T-6 heat-treated hypereutectic aluminum for superior strength.
This complete kit includes the piston, rings, wrist pin, and retainers.

Part Number Matrix

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

Brand	Part Number	Notes
Mercury	850026T3	Piston only
Mercury	705-850026T3
Mercury	705-850026A3
Mercury	39-821695A4	Kit with rings

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This piston kit is compatible with specific 2-cylinder engines from Mercury and Mariner.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury	30 (2 CYL.)	30	2-Stroke	1998–2006	850026T3	Crankshaft-Piston-Flywheel assembly
Mercury	40 (2 CYL.)	40	2-Stroke	1998–2006	850026T3	Crankshaft-Piston-Flywheel assembly
Mariner	30 (2 CYL.)	30	2-Stroke	1998–2006	850026T3	Crankshaft-Piston-Flywheel assembly
Mariner	40 (2 CYL.)	40	2-Stroke	1998–2006	850026T3	Crankshaft-Piston-Flywheel assembly

Technical Specs

Product Type: Piston Kit
Installation: Engine Specific
Fuel Type: Gasoline
Housing Material: Hypereutectic Aluminum Alloy
Dimensions: 2.993" (76.02 mm) Diameter
Weight: 1.13 lbs (0.51 kg)
Finish: T-6 Heat Treated, Hard Anodized Coating on Top
Max Temperature: 1560°F
Hardness: HV280-400

What’s in the Box

1 x Piston
1 x Ring Set
1 x Wrist Pin
2 x Retainers

Installation Notes

Ensure the engine is off and cool. Disconnect the battery and fuel supply for safety.
Drain the engine coolant and oil completely to prevent spills.
Carefully remove the cylinder head and any other components obstructing access to the piston.
Remove the old piston assembly from the connecting rod.
Thoroughly clean the cylinder bore and inspect for any scoring or wear. Confirm dimensions are within spec.
Carefully install the new rings onto the new piston according to the ring manufacturer's instructions.
Liberally lubricate the piston, rings, and cylinder wall with fresh engine oil.
Use a piston ring compressor to gently install the new piston assembly into the cylinder.
Reassemble all components in reverse order, torquing all fasteners to the manufacturer's specifications.
Refill the engine with fresh oil and coolant before starting.
Run the engine briefly and check for any leaks or unusual noises.

Troubleshooting & FAQ

How do I know if this piston kit fits my engine?

This kit is specifically designed for Mercury and Mariner 30-40 HP 2-stroke outboard engines from 1998–2006. To ensure a perfect fit, please verify your engine's model, year, and serial number range against our compatibility chart. Cross-referencing the OEM part number (850026T3 or equivalents) is the most reliable method.

What are the signs of a failing piston?

Common symptoms of piston failure include a noticeable loss of engine power, excessive blue or white smoke from the exhaust, audible knocking or rattling sounds from the engine, and the presence of metal shavings in the engine oil.

Does this aftermarket kit include piston rings?

Yes. This aftermarket piston kit is a complete set that includes the piston, piston rings, wrist pin, and retainers. This is a key difference from the OEM Mercury part 850026T3, which is sold as a piston only.

What is the main difference between this piston and the OEM version?

Our piston is manufactured from a modern hypereutectic aluminum alloy with a hard-anodized coating on the top. This provides superior strength, heat resistance, and wear characteristics that meet or exceed original OEM specifications.

When should a piston be replaced?

Pistons should be replaced during a scheduled major engine overhaul or immediately if you detect signs of failure like loss of compression or engine knock. The lifespan depends heavily on usage hours, maintenance quality, and operating conditions.

Is any special machining required for installation?

This is a standard-sized piston kit. It should be a direct fit for a cylinder that is within standard factory tolerances. If your cylinder is worn or scored, it may need to be machined (bored) to the next oversize, which would require a corresponding oversize piston kit.

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.

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