Piston Ring Set (0.25MM Oversize) – Fits Yamaha/Mariner 6/8 HP 2-Stroke (Replaces 647-11610-10, 39-80423M)
Piston Ring Set (0.25MM Oversize) – Fits Yamaha/Mariner 6/8 HP 2-Stroke (Replaces 647-11610-10, 39-80423M) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
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Piston Ring Set (0.25MM Oversize) – Fits Yamaha/Mariner 6/8 HP 2-St...
Product Details
This Piston Ring Set (0.25MM Oversize) is designed for Yamaha and Mariner 6HP and 8HP 2-stroke outboard engines, commonly found in E8D, 677, and B model series from the 1980s and 1990s. It is a first-oversize set intended for use after a cylinder has been rebored.
This set serves as a direct replacement for Yamaha P/N 647-11610-10 and Mariner/Mercury P/N 39-80423M, ensuring a precise match for engine rebuilds.
- For engine rebuild and repair requiring a +0.25MM oversize.
- Designed for gasoline/petrol 2-stroke mix fuel types.
- Package includes two complete ring sets, enough for a two-cylinder engine.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yamaha | 647-11610-10 |
| Mariner | 39-80423M |
| Mercury | 39-80423M |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This set is intended for specific 2-stroke engines from Yamaha and Mariner. Verify your engine's model and part number before ordering.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | E8D | 8 | 2-Stroke | 1998+ | 647-11610-10 | For 677 engine code |
| Yamaha | 6B/8B | 6/8 | 2-Stroke | 647-11610-10 | B series engines | |
| Mariner | 6/8 HP | 6/8 | 2-Stroke | 39-80423M | Equivalent to Yamaha part |
Technical Specs
- Product Type
- Piston Ring Set (0.25MM Oversize)
- Installation
- Engine rebuild/repair
- Fuel Type
- Gasoline/petrol (2-stroke mix)
- Dimensions
- 0.25MM oversize from standard specification
- Product Dimensions
- 7.6cm x 1.0cm x 7.6cm
- Fitting Type
- Internal engine component
- Other Technical Attributes
- First oversize (+0.25MM) piston ring set for cylinder rebore
What’s in the Box
- 2 x PISTON RING SET (0.25MM O/S) (647-11610-10)
Installation Notes
- Disconnect the battery and all fuel lines to ensure a safe working environment.
- Drain engine oil and coolant. Proceed to remove the cylinder head and cylinder block from the powerhead.
- Carefully extract the old pistons from the cylinders and use a ring expander tool to remove the worn piston rings.
- Thoroughly clean the piston ring grooves and cylinders, inspecting for any scoring or damage. This is critical for proper ring seating.
- Install the new 0.25MM oversize piston rings onto the pistons, ensuring the correct orientation as per your engine's service manual.
- Generously lubricate the new rings, pistons, and cylinder walls with fresh 2-stroke engine oil before reassembly.
- Use a piston ring compressor tool to carefully guide the pistons back into the cylinders, preventing ring damage.
- Reassemble all engine components in the reverse order of disassembly, ensuring all bolts are torqued to manufacturer specifications.
Troubleshooting & FAQ
How do I know if I need oversize piston rings?
Oversize rings are required after a cylinder has been bored (machined to a larger diameter) to correct for wear, tapering, or scoring. You must have a machine shop measure the cylinder bore to confirm if a +0.25MM oversize is the correct size for your specific engine rebuild.
Are these rings for one piston or the whole engine?
This package contains two complete piston ring sets, which is enough to service a standard two-cylinder Yamaha or Mariner 6/8 HP engine. Each set outfits one piston.
What are the signs of failing piston rings?
Common symptoms include excessive blue or white exhaust smoke, a noticeable loss of engine power and compression, increased oil consumption between changes, and persistent oil fouling on the spark plugs.
Can I install these without reboring the cylinder?
No. These 0.25MM oversize rings are specifically designed for cylinders that have been machined to a larger diameter. Installing them in a standard, non-bored cylinder will cause immediate binding, engine seizure, and catastrophic failure.
What tools are recommended for installation?
Using a dedicated piston ring expander for installation and a piston ring compressor for inserting the piston into the cylinder is highly recommended. These tools help prevent bending, breaking, or incorrectly seating the new rings.
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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