15/04/2017
Embarking on an engine rebuild for your Sea-Doo 717/720cc personal watercraft can seem daunting, but with the right knowledge and components, it's a rewarding project. Understanding cylinder compatibility, piston types, and the nuances of engine parts suppliers like SBT is crucial for a successful and lasting repair. This comprehensive guide aims to demystify these aspects, ensuring you have the clarity needed to make informed decisions for your PWC's heart.
One of the most common initial queries revolves around component compatibility, specifically concerning aftermarket parts. Let's dive straight into whether a WSM cylinder will integrate seamlessly with your Sea-Doo 717/720cc engine.
WSM Cylinder Compatibility for Sea-Doo 717/720cc Engines
For those looking to replace or upgrade their Sea-Doo 717/720cc cylinders, the good news is that WSM offers a compatible solution. The WSM cylinder kit is specifically designed to fit all Sea-Doo 717/720cc Silver & white engines. This broad compatibility simplifies the selection process, providing a reliable aftermarket option for many owners. However, compatibility is just one piece of the puzzle; understanding the characteristics of the parts themselves is equally vital.
Understanding Piston Types: WSM vs. Wiseco
When it comes to pistons, you'll often encounter two primary types: cast and forged. WSM and Wiseco are prominent brands, each offering distinct advantages based on their manufacturing processes.
WSM Pistons: The Cast Advantage
WSM pistons are typically full cast, meaning they are formed by pouring molten aluminium into a mould. This manufacturing method makes them generally more cost-effective. WSM pistons commonly come equipped with high-performance Rik Japanese rings. Cast pistons are an excellent choice for standard engine rebuilds and recreational use, offering good durability under normal operating conditions. They are designed to expand and contract at a rate similar to the cylinder bore, which can be beneficial for consistent performance.
Wiseco Pistons: The Forged Strength
In contrast, Wiseco pistons are forged. The forging process involves shaping solid aluminium under extreme pressure, resulting in a much denser and stronger material structure. This increased strength makes forged pistons ideal for high-performance applications, where engines operate under higher temperatures and pressures. Wiseco pistons exclusively use Wiseco high-performance rings, which are engineered to complement the robust nature of their forged pistons. While generally more expensive, forged pistons offer superior resistance to fatigue and deformation, making them a preferred choice for enthusiasts seeking maximum durability and performance.
Cast vs. Forged Piston Comparison
| Feature | WSM (Cast Piston) | Wiseco (Forged Piston) |
|---|---|---|
| Manufacturing Method | Molten aluminium poured into a mould | Solid aluminium shaped under extreme pressure |
| Material Density | Good | Higher, denser material |
| Strength & Durability | Suitable for standard/recreational use | Superior; ideal for high-performance/heavy use |
| Cost | Generally more cost-effective | Typically higher |
| Rings Included | Rik Japanese high-performance rings | Wiseco high-performance rings only |
| Thermal Expansion | Designed to match cylinder bore expansion | Can require slightly looser initial clearances due to different expansion rates |
Cylinder Preparation and Piston Sizing
Before installing new pistons, proper cylinder preparation is paramount. This involves careful inspection and, if necessary, machining of the cylinder bore.
Inspecting Your Cylinder Sleeves
Thoroughly inspect your existing cylinder sleeves for any signs of damage. Look for heavy scoring, chipping, and cracks. Even minor damage can compromise engine performance and longevity. If severe damage is present, a simple hone might not suffice, necessitating more extensive work or even replacement.
Standard vs. Oversize Pistons
The decision between standard size and oversize pistons hinges on the condition of your cylinder bore:
- Standard Size Pistons: Order these if you are only honing your cylinders. Honing is a process that cleans up the cylinder walls, removing minor imperfections and creating a cross-hatch pattern that helps retain oil for lubrication. This is suitable if the bore is still within specification and only requires a light clean-up.
- Oversize Piston Kits: If your cylinder bore exhibits more significant damage and will not clean up effectively at standard size, you'll need to order the correct oversize piston kit. This means the cylinder will need to be bored out to a larger diameter to accommodate the new, larger piston.
Understanding Bore Damage and Machining Limits
It's critical to understand the limits of cylinder machining. Remember that 1.00mm is equivalent to .040 inches. When reboring your cylinder, you can typically only cut up to .020 inches into your cylinder wall for it to clean up for finish honing. This means there's a finite amount of material that can be removed before the cylinder becomes too thin or out of specification.
If the damage to your cylinder bore is deeper than this .020-inch limit, or if there are significant cracks or chips, simply boring will not resolve the issue. In such cases, you will need the cylinder sleeve replaced entirely. After replacing the sleeve, it must then be bored to the finish size required for your new piston. This is a precise process that should ideally be performed by a professional machine shop to ensure accuracy and proper clearances.
SBT and Sea-Doo Motor Sales: What You Need to Know
SBT (Short Block Technologies) is a well-known supplier of remanufactured personal watercraft engines and components. Yes, SBT does indeed sell Sea-Doo motors, offering a convenient solution for those needing a full engine replacement rather than a rebuild of individual components.
The Core Exchange System Explained
SBT operates primarily on a core exchange basis. Understanding this system is crucial for a smooth transaction and to avoid additional charges.
What is a Core?
The 'core' refers to your old engine, crankshaft, cylinders, or any other primary component that was included in your purchase. It's essentially the used part you're replacing. The core must be returned to SBT to complete the exchange part of your purchase agreement.
Core Requirements and Timelines
To avoid late fees, your core must include all of the like parts that were included in your purchased item (even down to the nuts and bolts) and must be returned to SBT within 14 days of receipt of your purchased item. This strict timeline ensures a consistent flow in their remanufacturing process.
Crucially, SBT does not accept aftermarket parts or ported cylinders/cases as cores. The core must be an original, un-modified component suitable for remanufacturing. This policy ensures the quality and consistency of their remanufactured products.
Shipping and Core Deposit Policies
- Continental US Orders: For customers within the continental United States, exchange items are typically based on a round-trip shipping charge, meaning the cost of shipping the new item to you and the core back to SBT is factored in. SBT generally does not charge a core deposit upfront for US sales. However, it's vital to remember that all pricing is on an exchange basis, assuming the timely return of your core. Failure to return the core within the specified timeframe will result in additional charges, as you would then effectively be purchasing the new item outright without the exchange discount.
- International Orders: For all customers outside the Continental US, the core exchange process is different. International customers are required to send their core exchange prior to the shipment of the exchange goods. This 'core-first' policy mitigates risks associated with international shipping and ensures SBT receives the core before dispatching the new product. For more detailed information, international customers are advised to refer to SBT's International Sales page or contact their international sales team directly.
The core exchange system is designed to make engine replacement more affordable by recycling old parts, but it places a responsibility on the customer to return the core promptly and in an acceptable condition.
Key Considerations for a Successful Rebuild
Beyond cylinders and pistons, a successful engine rebuild involves several other critical factors:
- Professional Machining: For any boring or significant cylinder work, relying on a reputable machine shop is highly recommended. Their expertise ensures precise measurements and finishes, which are vital for engine longevity.
- Proper Gaskets and Seals: Always use new, high-quality gaskets and seals during assembly. Reusing old ones can lead to leaks and engine damage.
- Assembly Lubrication: Use appropriate assembly lube on all moving parts during installation to protect them during the initial startup before the engine's oiling system fully pressurises.
- Break-in Procedure: Follow the manufacturer's recommended break-in procedure for your newly rebuilt engine. This typically involves specific operating guidelines for the first few hours to allow components to seat properly and prevent premature wear.
Frequently Asked Questions
What's the main difference between cast and forged pistons?
The main difference lies in their manufacturing process and resulting strength. Cast pistons (like WSM) are poured into a mould and are suitable for standard use, while forged pistons (like Wiseco) are formed under extreme pressure, making them significantly stronger and ideal for high-performance applications. Forged pistons offer superior durability under stress.
When should I order an oversize piston kit?
You should order an oversize piston kit if your cylinder bore has significant damage (e.g., deep scoring, excessive wear) that cannot be cleaned up by simple honing. This requires the cylinder to be bored out to a larger diameter to accommodate the larger piston.
What happens if my cylinder damage is too deep for reboring?
If the damage exceeds the machining limit (typically .020 inches for cleanup), or if there are severe cracks, the cylinder sleeve will need to be replaced. This is a more involved process where the old sleeve is removed, a new one is installed, and then bored to the correct finish size.
How long do I have to return my core to SBT?
You have 14 days from the receipt of your purchased item to return your core to SBT to avoid late fees. Ensure all original parts are included.
Can I send an aftermarket cylinder or a ported engine as a core to SBT?
No, SBT explicitly states that they do not accept aftermarket parts or ported cylinders/cases as cores. The core must be an original, un-modified component.
Understanding these critical aspects of engine repair and component sourcing will empower you to tackle your Sea-Doo 717/720cc engine rebuild with confidence. By choosing the right parts, preparing your cylinders correctly, and navigating supplier policies effectively, you'll ensure your personal watercraft is back on the water, performing optimally for many seasons to come.
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