Peter’s Thruxton

The majority of the motorcycles that we feature, no matter how customised they may look, are mechanically standard. This is because many of the donor motorcycles, although cosmetically shabby, have sound engines and gearboxes. Overhauling a sound and reliable engine adds a great deal to the already high cost of building a custom motorcycle, no matter what the style of the build. A policy of “why scratch if it doesn’t itch” is adopted. When a donor motorcycle has an unserviceable engine which must be overhauled, the engine is usually rebuilt back to the original manufacturer specifications due to the cost and lack of availability of performance parts. Not many of the amateur or professional builders have the necessary expertise to build and tune performance engines. In any case, most of these motorcycles perform more than adequately in standard form to satisfy their builder’s requirements. There are however some builders who believe a lot of go is part of the show…

It is hard to believe, based on his reputation, that building performance Triumph parallel twin engines is actually only a passionate hobby for Peter Moody, a full time electrical engineer by profession. Peter built the racing spec motor for Rob’s Triton and also rebuilt the motors of several of the Triumph bobbers that we have featured. His own racing Triton has been clocked at 190km/h at the East London circuit. We hope to feature this motorcycle soon. It goes without saying that Peter’s own beautiful Triumph Bonneville Thruxton Replica, our featured motorcycle, will be a good performer.

The head of Triumph going into the 1960s was the brilliant engineer, Edward Turner. It was Turner’s belief that road racing, such as GP racing, was a very good way of winding up bankrupt. Triumph’s official involvement in racing was thus minimal. There was however one racing event in which Triumph saw marketing value and that was a five hundred mile endurance race for basically standard production motorcycles. This race was held annually at the Thruxton racetrack in the south of England. Although the name Thruxton had unofficially first been coined to describe 1959 Bonnevilles destined for racing, officially the true Thruxtons were the 52 racing Bonnevilles produced in 1964 and 1965 for homologation purposes. Dealers were however encouraged to build their own Thruxtons and so many more examples were actually produced. It is a replica of these Thruxtons that Peter has built using a 1970 Bonneville 650.

Cosmetically, Peter has installed a Thruxton replica seat and top half fairing imported from British Triumph specialists, George Hopwood Classic Restorations. He also has the full fairing but prefers to show off the beauty of the Bonneville engine. The blue petrol tank and white mudguards and fairing were the standard Thruxton colour combination. Peter has gone to great lengths to replicate the original Thruxton elements, such as the shallow drop clubman handlebars.

The engine is definitely the heart of the Thruxton. The engine capacity is still 650cc but racing quality Arrow Precision conrods have been installed with lightened, cut away “slipper” pistons which make the engine easier to balance, allowing for extra revs to be produced. The primary chain has been replaced with a belt drive. BSA Spitfire profiled Triumph cams were supplied by George Hopwood, as were the cut away sidecover and oil tank to allow for the long carb bell mouths.  The Amal carbs are standard but have been reworked by Peter. Not much on a Triumph engine is not “reworked” by Peter!  Although not fitted as standard on the original Thruxtons, Peter has installed a pair of British made Feked Motorcycle Parts swept back header pipes. He originally fitted the long silencers which were fitted on Thruxtons but found that tuning the bike was impossible and opted for the short silencers instead.

As was originally the case, many of the Thruxton’s components were standard on all Bonnevilles. The gorgeous twin leading shoe drum brakes are an example. Although not visible on the photos, Peter has drilled large holes in the hubs on the opposite side to these brakes, which was standard on the lightened Thruxton. As can be evidenced by the close up photos, everything on the bike is spot on, even though it gets ridden often and over long distances.

At a time when cafe racers are being built out of the most unlikely motorcycles, it is good to be able to occasionally feature a classic benchmark machine from that bygone era, just to remind us where it all began and what it was all about. Peter’s lovely Thruxton is one of those classics.