Mercruiser Shim Kit – Fits Mercruiser Sterndrive (Replaces 15-38657A1)
Mercruiser Shim Kit – Fits Mercruiser Sterndrive (Replaces 15-38657A1) 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).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Mercruiser Shim Kit – Fits Mercruiser Sterndrive (Replaces 15-38657A1)
Product Details
This Mercruiser Shim Kit is engineered for shimming applications in Mercruiser sterndrives, including Alpha One (1984–1990) and Alpha One Gen II (1991 and up) models. It provides the necessary components for setting correct gear clearances during assembly or repair.
It serves as a direct replacement for Mercury/Mercruiser part number 15-38657A1.
- Application: Used for setting gear backlash and bearing preload in the sterndrive upper gearcase.
- Installation: Requires specialized tools and strict adherence to the official service manual for precision adjustment.
- Material: Manufactured from high-strength metal to ensure accurate tolerances and lasting durability.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket suppliers.
| Brand | Part Number |
|---|---|
| Mercury/Mercruiser | 15-38657A1 |
Engine & Model Compatibility
Confirm your engine model and year in the table below to ensure fitment.
For Mercruiser applications, check your sterndrive model and year range to ensure this part is a correct fit.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. |
|---|---|---|---|---|---|
| Mercruiser | Alpha One | Various | 4-Stroke | 1984–1990 | 15-38657A1 |
| Mercruiser | Alpha One Gen II | Various | 4-Stroke | 1991 and up | 15-38657A1 |
Technical Specs
- Product Type
- Shim Kit
- Application
- Engine/Sterndrive Component
- Material
- Metal (Steel/Aluminum)
- Dimensions
- Height: 0.6 cm, Width: 11.0 cm, Length: 8.0 cm
- Weight
- 0.01 kg (0.022 lb)
What’s in the Box
- 1 x Shim Kit (Replaces 15-38657A1)
Installation Notes
- Always consult the official Mercruiser service manual for your specific sterndrive model before beginning work. These instructions are generic and not a substitute for the manufacturer's guide.
- Secure the vessel, disconnect the battery, and drain the gearcase lubricant completely.
- Disassemble the upper unit of the sterndrive to access the gear assembly, carefully following the procedures in your service manual.
- Using specialized tools (e.g., a dial indicator and alignment fixtures), measure the existing gear backlash and bearing preload to determine the required adjustment.
- Based on your measurements, select the appropriate combination of shims from this kit to achieve the manufacturer's specified tolerances.
- Install the new shims and re-measure to confirm the adjustment is correct. This step is critical and may require patience to get right.
- Reassemble all components in the reverse order of disassembly. Ensure all seals and gaskets are replaced and all fasteners are torqued to the correct specification.
- Refill the gearcase with new, recommended marine lubricant to the proper level. Reconnect the battery and test the drive's operation before returning to service.
Troubleshooting & FAQ
What is this shim kit used for?
This kit provides the necessary shims to set the correct gear backlash and bearing preload in the upper gear housing of Mercruiser Alpha One and Gen II sterndrives. Proper shimming is a critical adjustment for quiet operation and preventing premature gear and bearing wear.
How do I determine the correct shim thickness to use?
The correct shim thickness is determined by taking precise measurements with specialized tools like a dial indicator, as outlined in the official Mercruiser service manual for your drive model. It is a precision task and should not be guessed or done by trial-and-error.
Will this kit fit my Mercruiser Bravo sterndrive?
While part number 15-38657A1 is used on some Bravo applications, we have not confirmed the full list of compatible models or years. To ensure a correct fit, please verify this part number against the requirements for your specific Bravo drive's serial number using an official parts diagram or service manual.
What are the symptoms of incorrect shimming?
Symptoms of improper shimming include a persistent whining or howling noise from the sterndrive (especially when turning or changing speed), excessive heat from the upper gearcase, and in severe cases, catastrophic gear failure. These shims correct for manufacturing tolerances and are chosen at assembly; they typically do not "wear out" but must be replaced if the drive is rebuilt with new gears or bearings.
Is this an OEM part?
This listing is for an aftermarket replacement part, not an original equipment manufacturer (OEM) component. It is built to meet or exceed OEM-level specifications using comparable materials and manufacturing processes. All our parts are produced in an ISO 9002 certified facility and are batch-inspected for quality and consistency.
How fast is shipping?
We ship worldwide from our closest fulfillment center to ensure fast delivery, with typical transit times of 5–15 days for most regions. Standard shipping is free for all orders. Expedited shipping options and exact costs are displayed at checkout where available.
What is the warranty and return policy?
This product is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter any issues, please contact our support team with your order details for assistance. Returns are accepted within our standard window for items that are unused and in their original condition. See our full policy page or reach out for return instructions.
Safety & Important Info
- Always verify the product images and specifications against your original part before purchasing. If anything appears different—even if your model is listed as compatible—do not order.
- This is an aftermarket replacement part, not an OEM component. Brand names and part numbers are used for reference purposes only.
- Professional installation is strongly recommended for all marine parts to ensure safety, proper function, and optimal performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world reliability.
- Fast Global Fulfillment — With partners worldwide, we offer free standard delivery to most regions, typically arriving in 5–15 days.
- Manufacturer-Direct Value — Our model delivers fair pricing without ever compromising on materials or quality control.
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