Rebuilding a Vincent Twin Engine: A Deep Dive

The question of whether to rebuild a Vincent twin engine is one that resonates deeply within the classic motorcycle community. For many enthusiasts, the Vincent represents the pinnacle of British engineering from the mid-20th century, a machine of legendary performance and distinctive design. However, the path to a fully restored Vincent is often a long and arduous one, fraught with challenges related to parts availability, complexity of design, and the sheer dedication required. This article aims to shed light on the process, using the personal experience of a long-term restoration project as a guide.

The Vincent Restoration Journey: A Personal Perspective

After a hiatus of nearly a decade, work recommenced on a Vincent Black Lightning Replica in November 2011. This wasn't a simple continuation, but rather a common enthusiast's trait of flitting between projects. The Norton International restoration had taken a backseat, with the Vincent lump beckoning from its stand. The goal was clear: to get the Vincent to a state where it could be displayed, even if not fully finished. This update focuses on the progress made, specifically on the primary drive assembly, a critical and complex part of the Vincent twin engine.

Revisiting the Gearbox: A Prerequisite for Progress

Before delving into the primary drive, a nagging concern from the previous build phase needed addressing: the gearbox's gear change. The author recalls spending considerable time on the gearbox, noting that the entire cluster, including substantial bearings and shafts, could be removed via the circular gearbox end cover. A genuine Black Shadow/Lightning selector plate, lighter than its Rapide counterpart, had been fitted. Despite initial worries about the gear change feel, a temporary re-test with the outer gearbox cover fitted confirmed that all four gears, and neutral, were engaging. While not perfect by hand, it was deemed sufficient to proceed, with real-world testing to follow once the bike is running.

The Vincent Primary Drive and Clutch: A Complex Heart

The Vincent twin's primary drive and clutch assembly is a testament to Vincent's philosophy: rugged, slightly quirky, and perhaps more complicated than strictly necessary. The clutch, often dubbed a 'servo clutch,' has a notorious reputation for being difficult to set up correctly, avoiding snatching or slipping. Historically, alternatives like the Suzuki GS750 multi-plate clutch were considered, involving machining a new inner body. However, the author's preference is to stick with the original Vincent clutch, aiming for the authentic Vinnie experience, especially now that the bike is intended for race parading rather than competitive racing.

Sourcing Quality Parts: The Maughan Legacy

A significant portion of the restoration involved sourcing parts, often from the Maughan family, renowned suppliers of high-quality Vincent components. The author recounts procuring consumables over many years, often funding these purchases by selling other bikes. These visits to Maughan's were described as being like a "kid in a candy shop," admiring the quality of their work, particularly the stainless steel cosmetic parts. The attention to detail, such as burnished hex faces on nuts, exemplified the high standards.

The approach taken was to replace anything that looked worn or dubious, "damn the expense," recognising that skimping on a Vincent engine could lead to very costly consequences. This foresight means that many new parts purchased 15 years ago are now ready for installation.

Sprocket Choices: Standard vs. Picador

A key decision involved choosing the engine sprocket. The author possessed a lightened, one-tooth-less sprocket from a Vincent Picador engine, originally intended for pilotless drone planes. This sprocket, drilled for lightness, appealed greatly. However, fitting it revealed a problem: the primary chain became too slack, with the tensioner unable to compensate. This led to the reluctant decision to revert to the standard engine sprocket for the time being, though the Picador sprocket remains a possibility for future consideration.

The Vincent Shock Absorber: A Unique Design

The primary drive incorporates a shock absorber mechanism, a departure from the rubber inserts found in later Norton clutches. This system uses springs to buffer the initial shock of throttle application. The author replaced the original, worn shock absorber springs, noting that spring breakage is a common fault. The PD5 plate, part of this system, is often fitted with its indents facing outwards, a modification believed to prevent premature spring breakage.

Fitting the Primary Chain and Tensioner

With the standard sprocket chosen, the assembly of the primary chain and tensioner proceeded. The primary chain is a critical component; a broken chain can cause catastrophic damage to the crankcases. A new, triple-row chain was fitted. The chain tensioner, a simple yet effective design, is adjusted via a bolt protruding from the lower crankcase, allowing for easy rider adjustment. The importance of lubrication, even during assembly, is stressed, with a comment on the lack of grease in some modern restoration shows.

The Primary Drive Cover: A Masterpiece of Casting

The final stage of this particular update involved fitting the substantial primary drive cover. The author expresses admiration for the quality of Vincent castings, highlighting the crisp lines and excellent finish of this component, which was painted and prepared 15 years prior. The cover features a tight-fitting lip and an oil seal to prevent oil from migrating into the clutch cavity. The process of fitting the cover required careful alignment of the rear sprocket with the oil seal, a task made easier by the clutch shoe carrier, which helps centralise the sprocket.

The PD8 ring, responsible for securing the shock absorber springs, is typically fitted with its indents facing inwards as designed. However, a common modification is to face them outwards to prevent spring breakage. The author followed this prevalent advice. The HRD inspection cap, an iconic feature of Vincent motorcycles, was also fitted.

Conclusion: A Glimpse of the Finished Product

The completion of the primary drive assembly and the fitting of the cover marked a significant milestone. The engine, with its gleaming black finish, was beginning to resemble the intended Black Lightning replica. The attention to detail, from the choice of sprockets to the careful fitting of seals and the iconic inspection cap, underscores the dedication required for such a restoration. The question of whether to rebuild a Vincent twin engine ultimately boils down to passion, patience, and a deep appreciation for these remarkable machines.

Frequently Asked Questions

Are Vincent spare parts good quality?

The quality of Vincent spare parts can vary. Historically, parts sourced from reputable suppliers like the Maughan family are considered to be of very high quality. However, as with any classic motorcycle, it's crucial to research and source parts from trusted vendors who understand the specific requirements and tolerances of Vincent engines.

Does a Vincent have a sump?

No, Vincent motorcycles operate a dry sump lubrication system. This means they have a separate oil tank instead of an engine sump to hold the oil. There is no room for oil to accumulate at the bottom of the engine.