Yamaha Piston Kit +0.50mm – Fits Yamaha 40HP 2-Stroke Outboard (Replaces 66T-11636-00, 66T-11636-01)
Yamaha Piston Kit +0.50mm – Fits Yamaha 40HP 2-Stroke Outboard (Replaces 66T-11636-00, 66T-11636-01) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Product Details
This aftermarket Yamaha Piston Kit +0.50mm is designed for Yamaha 40HP 2-Stroke outboard engines, including models E40X, 40XMH, E40XMH, E40XW, and E40XWT from approximately 1998–2001. It is specifically for cylinders that have been machined to an 80.50mm oversize bore.
This kit serves as a direct replacement for Yamaha OEM part numbers 66T-11636-00 and 66T-11636-01.
- Fits cylinders honed to a +0.50mm oversize (80.50mm).
- Constructed from durable aluminum alloy for reliable performance.
- The complete kit includes the oversize piston and a matching ring set.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yamaha | 66T-11636-00 |
| Yamaha | 66T-11636-01 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This part is documented to fit the following Yamaha outboard models. Ensure your cylinder has been prepared for a +0.50mm oversize piston.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | E40X | 40 | 2-Stroke | 2000–2001 | 66T-11636-00 | +0.50mm Oversize |
| Yamaha | 40XMH | 40 | 2-Stroke | 2001–2006 | 66T-11636-00 | +0.50mm Oversize |
| Yamaha | E40XMH | 40 | 2-Stroke | 2001–2006 | 66T-11636-00 | +0.50mm Oversize |
| Yamaha | E40XW | 40 | 2-Stroke | 2001–2006 | 66T-11636-00 | +0.50mm Oversize |
| Yamaha | E40XWT | 40 | 2-Stroke | 2001–2006 | 66T-11636-00 | +0.50mm Oversize |
Technical Specs
- Product Type
- Piston Kit (+0.50mm Oversize)
- Installation
- Engine Cylinder
- Fuel Type
- Gasoline (2-Stroke Oil Mix)
- Housing Material
- Aluminum Alloy
- Piston Diameter
- 80.50mm (3.17 in)
- Product Dimensions
- 8.5 × 8.5 × 8.5 in
- Weight
- 0.50 LBS (0.23 kg)
- Bore Specification
- Oversize +0.50mm from standard 80mm bore
What’s in the Box
- 1 x Piston Assembly (+0.50mm Oversize) (66T-11636-00)
- 1 x Piston Ring Set (66T-11603-00)
Installation Notes
- Disconnect the battery and fuel supply for safety.
- Drain the engine coolant and oil completely.
- Remove the cylinder head and any obstructing components to access the pistons.
- Carefully push the old piston out from the connecting rod.
- Have a professional machine shop inspect and hone the cylinder to the required 80.50mm dimension.
- Install the new piston rings onto the new piston, ensuring gaps are correctly oriented.
- Lubricate the new piston, rings, and cylinder wall with fresh 2-stroke engine oil.
- Install the new piston assembly, confirming its orientation according to service manual diagrams.
- Reassemble the engine components in reverse order, torquing all bolts to the manufacturer's specifications.
- Refill with fresh coolant and oil.
- Follow a proper engine break-in procedure, typically running at varied, low-to-mid RPMs for the first 10 hours.
Troubleshooting & FAQ
How do I know if I need an oversize piston?
An oversize piston is required when the engine cylinder is worn or damaged beyond standard service limits. The cylinder must be bored or honed by a machine shop to the next size up. This +0.50mm piston is for cylinders machined to a final diameter of 80.50mm.
Will this fit my standard 80mm cylinder bore?
No. This is an oversize part and is 0.50mm larger than the standard piston. It will not fit in a standard cylinder bore and requires the cylinder to be professionally machined to 80.50mm.
What are the signs of a failing piston?
Common symptoms include a loss of compression, excessive oil consumption, blue or white smoke from the exhaust, reduced power, and an audible knocking or rattling sound from within the engine.
Does this kit include the wrist pin and clips?
Yes, the "Piston Assembly" listed in the package contents includes the piston, wrist pin, and circlips required for installation, along with the separate piston ring set.
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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