15/06/2019
The Yamaha RD350 YPVS, a legendary two-stroke machine, holds a special place in the hearts of many motorcycle enthusiasts across the UK. Its exhilarating performance and distinctive sound are intrinsically linked to the health of its engine, particularly the crankshaft. As a high-revving, pressed-together assembly, the crankshaft is the very heart of your YPVS, responsible for converting the pistons' linear motion into the rotational power that drives your bike. Over time, even the most robust components succumb to wear and tear, making a professional crankshaft rebuild not just a recommendation, but a crucial step in preserving your cherished machine's performance and longevity.
- Understanding the RD350 YPVS Crankshaft's Unique Design
- Why a Professional Crankshaft Rebuild is Indispensable
- The PJ Motorcycle Engineers Approach to RD350 YPVS Crank Rebuilding
- Investment in Performance: Pricing and Upgrade Options
- Seamless Service: Turnaround and Payment
- Why Professional Expertise Matters for Your YPVS
- Frequently Asked Questions About RD350 YPVS Crank Rebuilds
- What are the tell-tale signs my RD350 YPVS crankshaft needs attention?
- How does the 31K 1UA crank differ from other two-stroke cranks regarding rebuilds?
- Are the replacement parts genuine Yamaha or aftermarket?
- What is the advantage of upgrading to TZ style big end bearings?
- How long will a rebuilt crank last?
Understanding the RD350 YPVS Crankshaft's Unique Design
Unlike many four-stroke engines, the RD350 YPVS, typical of two-stroke powerplants, features a crankshaft that is pressed together rather than being a single, solid forging. This design allows for the installation of roller bearings directly onto the crank pins and main journals, crucial for the high rotational speeds and firing impulses of a two-stroke engine. However, what truly sets certain RD350 YPVS cranks apart, particularly the 31K 1UA models, is a specific design aspect concerning the crank pin.
On these specific models, the crank pin – the component upon which the crucial big end bearing rotates – is not a separate, universally replaceable item. Instead, it is an integral part of the inner flywheel web. This design choice, while robust in its original form, introduces a unique challenge when it comes to rebuilding. If there is any significant wear or damage to these crank pins, it necessitates the replacement of the entire inner web, rather than just the pin itself. This distinction is vital for understanding the rebuild process and potential costs.
Why a Professional Crankshaft Rebuild is Indispensable
Your YPVS's crankshaft endures immense forces and stresses with every revolution. Over thousands of miles, the bearings, con rods, and crank pins will inevitably wear. Ignoring the signs of a failing crankshaft can lead to catastrophic engine failure, turning a repairable issue into a much more costly, or even irreparable, problem. Common indicators that your crank needs attention include:
- Excessive vibration, particularly at higher RPMs.
- Unusual knocking or rattling noises emanating from the crankcases.
- A noticeable loss in engine performance or responsiveness.
- Increased difficulty in starting the engine.
- Play in the connecting rods when checked through the exhaust port.
A professional rebuild addresses these issues proactively, restoring the engine's balance, reducing harmful vibrations, and ensuring the smooth, reliable operation that the RD350 YPVS is renowned for. It's an investment in your bike's future, safeguarding its iconic performance for years to come.
The PJ Motorcycle Engineers Approach to RD350 YPVS Crank Rebuilding
At PJ Motorcycle Engineers, we specialise in the intricate process of RD350 YPVS crankshaft rebuilds, understanding the nuances of these exceptional engines. Our approach combines meticulous attention to detail with the use of high-quality components and expert craftsmanship.
Initial Assessment: Unveiling the Unknown
Due to the aforementioned design of the 31K 1UA crank, providing an exact rebuild quote without first stripping the crankshaft down is simply impossible. The condition of the inner flywheel webs, particularly the integral crank pins, cannot be fully assessed until a thorough inspection. If a big end bearing has suffered a failure, it is almost certain that the corresponding web will require replacement. However, for cranks with low hours and minimal damage, a standard rebuild might suffice without needing new webs. This initial, crucial step of disassembly allows us to accurately determine the necessary parts and provide a precise cost.
The Standard Rebuild Process: Precision and Quality Assured
Our standard crankshaft rebuild service is comprehensive, designed to restore your crank to optimal condition. It involves a series of critical steps:
- Complete Disassembly: Every component of the crankshaft assembly is carefully stripped down.
- Meticulous Cleaning and Inspection: All parts are thoroughly cleaned, and then rigorously inspected for any signs of cracks, fatigue, or excessive wear. This is a critical stage to ensure the integrity of reusable components.
- Premium Component Replacement: We replace all wear-prone parts with brand NEW, high-quality components. This includes:
- Con rods (connecting rods)
- Big end bearings (main lower rod bearings)
- Thrust washers (to control lateral play)
- Small end bearings (upper rod bearings)
- All four main bearings (supporting the crankshaft within the crankcases)
- The centre labyrinth seal (crucial for crankcase sealing and pressure separation)
We pride ourselves on using only premium-grade parts, sourced from reputable Japanese manufacturers such as Koyo / Hic Bearings and Long Brand Con Rods, ensuring durability and performance that meets or exceeds original specifications.
- Precision Assembly and Truing: The rebuilt crank is then assembled on a specialised jig. This ensures that the two halves of the crankshaft are perfectly phased at 180 degrees – a crucial factor for the smooth operation and balance of a two-stroke engine. Following assembly, the entire unit is meticulously trued by hand. This painstaking process guarantees that the crankshaft runs perfectly straight and balanced, ready to be dropped into your crankcases with confidence.
Addressing the 31K 1UA Crank Pin Dilemma
The unique integral crank pin design of the 31K 1UA RD350 YPVS inner flywheel webs is a significant consideration during the rebuild process. Here’s a breakdown of the implications:
| Crank Condition | Web Replacement Necessity | Cost Implication (per web) |
|---|---|---|
| Big End Bearing Failure (e.g., seizure, excessive play) | 100% Yes – Damage to the integral crank pin is almost guaranteed. | £37.50 + VAT |
| Low Hours / Minimal Wear / Standard Service | May or may not need replacing – inspection is key. | £0 - £37.50 + VAT (if required) |
Each new inner web required costs £37.50 + VAT, and since there are two inner webs, this can add a significant but necessary cost to the rebuild if damage is present. Our assessment ensures only truly necessary parts are replaced, providing transparency and value.
Investment in Performance: Pricing and Upgrade Options
The price for a standard, high-quality crankshaft rebuild at PJ Motorcycle Engineers is £280.00 + VAT. This comprehensive service includes all the new components and precision labour detailed above, providing exceptional value for the restoration of your engine's core.
For those seeking enhanced durability or planning for higher performance applications, we offer an upgrade option for the big end bearings. You can choose to upgrade to TZ style big end bearings for an additional £20.00 + VAT. These bearings are designed for increased robustness and are an excellent choice for riders who demand the utmost reliability from their YPVS, especially under sustained high-stress conditions.
Seamless Service: Turnaround and Payment
We understand that you'll be eager to get your YPVS back on the road. Our typical turnaround time for a crankshaft rebuild is approximately 10 days of workshop time. We operate on a policy of trust and convenience; payment is not required until your rebuilt crankshaft is fully prepared and ready to be dispatched back to you. We offer flexible payment options to suit your needs, including credit card, PayPal, or direct bank transfer, making the process as smooth as possible.
Why Professional Expertise Matters for Your YPVS
Rebuilding a two-stroke crankshaft is not a task for the inexperienced or ill-equipped. It requires specialised tools, deep understanding of engine dynamics, and meticulous precision. A poorly rebuilt crank can lead to severe engine damage, negating any initial cost savings. Entrusting your RD350 YPVS crankshaft to experienced professionals ensures:
- Correct Phasing and Truing: Essential for smooth running and preventing destructive vibrations.
- Quality Components: Assurance that only the best, most durable parts are used.
- Expert Inspection: Identification of hidden damage that might be missed by an untrained eye.
- Peace of Mind: Knowing your engine's heart has been restored to factory-level (or better) standards.
Frequently Asked Questions About RD350 YPVS Crank Rebuilds
We often receive questions regarding this vital service. Here are some of the most common:
What are the tell-tale signs my RD350 YPVS crankshaft needs attention?
Look out for increased engine vibration, especially through the handlebars and footpegs, a distinct knocking or rattling sound from the crankcases (which often worsens with RPM), or a noticeable loss of power and responsiveness. Any excessive lateral play in the connecting rods, visible by looking up the exhaust port, is also a clear indicator.
How does the 31K 1UA crank differ from other two-stroke cranks regarding rebuilds?
The primary difference for the 31K 1UA models is that the crank pin (the journal for the big end bearing) is integral to the inner flywheel web. This means if the crank pin is worn or damaged, the entire inner web must be replaced, rather than just a standalone pin. This can affect the overall cost if both webs require replacement.
Are the replacement parts genuine Yamaha or aftermarket?
We utilise high-quality aftermarket components from leading Japanese manufacturers. Brands like Koyo and Hic for bearings, and Long Brand for con rods, are renowned for their reliability and meet or often exceed the performance of original equipment parts. This ensures excellent longevity and performance for your rebuilt crank.
What is the advantage of upgrading to TZ style big end bearings?
TZ style big end bearings are designed for enhanced durability and robustness. They are particularly beneficial for engines that are regularly ridden hard, used in competition, or tuned for higher performance, offering an extra layer of reliability and peace of mind under demanding conditions.
How long will a rebuilt crank last?
The lifespan of a rebuilt crankshaft largely depends on riding style, regular maintenance, and proper engine break-in after the rebuild. With sensible riding and adherence to maintenance schedules, a professionally rebuilt crank using quality components can provide many thousands of miles of reliable service, often comparable to or exceeding the original factory lifespan.
Don't let a tired crankshaft diminish the thrill of riding your Yamaha RD350 YPVS. A professional rebuild is an investment that pays dividends in performance, reliability, and sheer riding enjoyment. If you're considering a rebuild, or simply have more questions about the process, don't hesitate to get in touch with our expert team at PJ Motorcycle Engineers. We’re here to ensure your YPVS continues to roar with the spirit it was built for.
Telephone: 01902 307457
Mobile Number For WhatsApp Messaging: 07884274838
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