A better KTT
Those Kiwis are an enterprising lot. A modern take on the legendary KTT Velocette is the latest to emerge from Phil Price’s fabulous stable.
At first sight Phil Price’s latest Velocette looks like another well prepared 350cc KTT from his collection, however on closer inspection, if you know about racing Velocettes, you realise that this is a very unusual machine. It is a copy of a 1936 Double Overhead Cam (DOHC) works engine housed in a replica of a 1952 works semi-duplex frame. This extraordinary Velocette is a product of Phil’s longterm friendship with Nick Thomson, Velocette aficionado and engineering guru. The inspiration for this 350 Velocette came whilst Phil and Nick were watching Bill Swallow, aboard the 250cc DOHC Eldee Velocette, compete in the 2014 Isle of Man Classic TT. It was becoming clear that the 250s were being sidelined and to be competitive in the 350 class (with ‘later’ model twins and multis now involved) a very special 350 Velocette was needed. They wanted to achieve a faster lap than any previous Velocette and possibly a 100mph lap; the “Holy Grail” for a Velocette. Phil and Nick quickly came to some simple conclusions to attain these goals; they needed more power, better handling, better suspension and a significant weight reduction. To achieve this they decided to carry on where the Velocette factory left off and being Kiwis they decided to undertake as much as possible themselves. Modern practice dictated a higher revving short stroke engine was the way to increase power output. The 350 KTT bore and stroke (73 x 81mm) never changed throughout its 25 year run (although there may have been an experimental short stroke engine towards the end). After considering the success of Velocette’s short stroke 250s, the success of other British 350s downsized to short stroke 250s and the highly successful Moto Guzzi 350s, they finally decided on a bore and stroke of 80 x 69mm. To build the ultimate 350 racing Velocette a number of choices had to be made, particularly which engine to use. The MK8 is an excellent vintage racer and their own highly tuned machine, with Chris Swallow on board, is very competitive.
“To build the ultimate 350 racing Velocette a number of choices had to be made, particularly which engine to use.”
However at 145kg it’s far too heavy to be competitive on the IoM. An obvious option, given the team’s experience, was an enlarged version of the Eldee Velocette. A further option was to replicate one of the Velocette works Double Overhead Cam models. Phil and Nick decided to copy a 1936 works DOHC engine, not the later engine as most pundits would expect. The main reasons for this surprising decision was the combustion chamber was much flatter, as was the valve included angle (more like current practice) and it matched well with the short stroke they intended to use. The bolt-on 1936 cambox design was also much simpler than the later integral design. The decision was made to stay as close to the original design and appearance as possible. The only major deviations from the original drawings were, a larger and steeper 34mm inlet tract, increased cylinder bore, a flatter valve included angle and coil valve springs (so much easier to keep oil tight). They also wanted to rectify a couple of well-known KTT issues, like the timing side main bearing. The KTT oil pump is an interference fit in the timing side crankcase and can distort the main-bearing. So they fitted a smaller outside diameter needle roller bearing and shrunk a steel plug into the pump cavity whilst boring the main bearing housing. The Crankshaft is dimensionally a reduced stroke Mk8 but with one-piece flywheels and mainshafts machined from single billets, the big-end runs on a pressed up parallel pin with expanding plugs and the balance factor is 76%. The one piece I-beam conrod, with a case hardened big end eye, was made from a billet by Nick. Ross Pistons supplied part-machined pistons blanks, which were then machined by Nick to create the valve cut outs, a squish band round the sides of the dome and a 12:1 compression ratio. Studying current valve-gear practice it was clear that more lift and overlap were required to exploit the higher revving short stroke engine. Cams were made that gave similar valve timings to a late 350 Manx Norton but with 460 thou lift on the inlet and 420 thou lift on the exhaust. The titanium 43mm inlet and 35mm exhaust valves were supplied by Ferrea. The drive to the camshafts is through a vertical splined shaft with bevel gears top and bottom, then to 5 gears driving the cams. The gears run on roller bearings and have Vernier adjustment for accurate valve timing. Nick made all the gear blanks and Bethany’s of Paraparaumu did the final gear cutting. A Morris magneto was used initially but after problems changed to a Pazon electronics unit in the IoM. Colin Quartly, one of New Zealand’s most experienced patternmakers, produced the engine and gearbox patterns following Velocette practice. Steve Howell, of CH tooling in Melbourne cast all the magnesium parts. The cambox is in itself a wonderful piece of form and function, machined from a solid billet of magnesium alloy to ensure dimensional accuracy and strength. The cylinder head is also a work of art, the enlarged inlet tract has been steepened, the included angle between the valves has been reduced, the combustion chamber is flatter and there is a ¾ inch skull cap around the combustion chamber. These modifications were blended into the original design such that the vintage exterior has been maintained. The team decided to copy the last works semi
“The cambox is in itself a wonderful piece of form and function, machined from a solid billet of magnesium alloy to ensure dimensional accuracy and strength.”
duplex frame and girder forks, and after some arm twisting, Ivan Rhodes lent them a late works frame to measure up. Nick extensively modified a standard road going RS frame to duplicate the works construction and bronze welded the final configuration. The effort required for all this, in particular the making of frame lugs, was significant. The MkV8 swinging arm was copied because it is stronger and better braced than the RS frame version.
Nick also fabricated a replica of the final racing girder forks that incorporated needle roller bearings. The steel lugs holding the needle rollers and fork tubes were cast using the lost wax process. The front end is extremely rigid, and true, with minimal friction compared to most telescopic forks. The final change was a combined spring and hydraulic damper unit engineered by Robert Taylor; it’s a mixture of Nitro and Olhins in the unit, a real improvement over the stiction-prone friction dampers. The development of the girder forks side links is a story in its own right. Girder forks follow a kind of S shaped curve, with a fairly straight line over the middle of their movement, but deviate significantly at the extremes, creating trail variations that can cause handling problems. The team also believed that more trail was needed but the MkV8’s front wheel is very close to the front down tube. The late works machines used smaller 19 inch front wheels, which allowed a bit more room to increase trail. Chris Swallow and the team experimented on a full scale MDF replica of the forks, steering head and side links and achieved near perfect movement and increased trail. The bottom pivot remained in the standard position on the centreline of the steering head and the top pivot was moved forward with a shorter link. Front wheel is standard 19 inch late MKVIII but with an internal double leading shoe linkage behind the brake plate, and the 18 inch rear wheel has an alloy hub, the same as an Mk8. The transmission was an easy choice – the same set up that has been used through years of short circuit racing in NZ – the Nova six speed gear cluster with a low first gear and an extended main-shaft, in a magnesium alloy gearbox casing. Primary drive is by a Synchroflex belt, which once set never needs adjusting. The aluminium clutch pulleys and basket uses off-the-shelf Suzuki friction plates. The Velocette final drive sprocket is outboard of the clutch which puts tremendous bending stress on the main-shaft and gearbox casing. The extended end of the main-shaft runs in an outboard needle roller bearing, significantly reducing the load on the main-shaft and gearbox. The crowning glory is the petrol tank which sits on the upper frame tubes, while the oil tank is unchanged from the road going item. The completed machine’s dry weight is a phenomenal 102kg and there are plans to shave off a few more kilos. Pukekohe in 2018 was its first outing after only being completed a few hours before the meeting started. Straight out of the box it ran well but with some inevitable teething issues, a great result for this ground up project. The second outing at the Burt Munro Challenge was even better, with a clean sweep at the Teretonga sprint races. Bill Swallow and Chris Swallow (both very experienced racers) took turns riding it and expressed their satisfaction with the way the machine performed. Although initial running was undertaken on methanol they quickly moved to petrol in preparation for the IoM. A very sleek fairing was also fitted. The trip to the 2018 Manx Grand Prix Classic TT was a series of highs and lows. The machine showed much promise in practice with nearly 123 mph in the speed trap and a 95 mph lap albeit with a couple of teething problems. In the first lap of the race Chris was the fastest single to Glen Helen, however he noticed the engine going off song at Ramsey,
scraped the pipe at the Verandah and cruised back to the pits. The back exhaust mount had fractured which caused the exhaust itself to fracture and fall down. This had been a problem in practice but the repaired mount also failed. Plans are already in place to return in 2019.
Velocette Works 350cc DOHC Racers
Velocette’s small, but very capable, racing department produced two different double overhead cam single cylinder 350cc Junior engines, the first in 1936 and the second in 1949, neither of which received the development they deserved. Percy Goodman built the prototype single overhead cam 350cc K engine Velocette in 1924, and after some refinements, the road-going KSS was launched in 1925. Percy along with Harold Willis also developed a works racing version with which Alec Bennett won the 1926 and 1928 Junior TTs. In 1929 Velocette offered a replica of the TT winning machine, the Mk1 KTT. In the early 1930s the works racers and customer KTT models went through a series of Mk models, improving performance, mechanical reliability and handling. By 1935 thoughts turned to better valve control at high revs for more power on the works machines. Stanley Woods, the consummate professional racer, joined the Velocette team in 1935 and was appalled by the handling of the works machines; he diagnosed poor weight distribution. After a series of tests with lumps of lead attached to the front downtube to improve weight distribution, the engines were moved far forward, by steepening the front downtube, on the works frames (copied on customer Mk.7 KTTs in 1937). Stanley was a convert of rear suspension after winning the 1935 Senior TT on a Moto Guzzi. He convinced Velocette to produce a swinging arm frame for the works machines (subsequently introduced on customer Mk.8 KTTs in 1938). In 1936 Velocette produced three works DOHC 350 singles with 4 speed positive stop gearboxes. The extensive use of magnesium alloy, (a fairly new and experimental metal) for the crankcases, gearbox shell, wheel hubs and brake
plates reduced weight to a minimum. The machines had a full loop frame with rear swinging arms and air/oil suspension units. Ted Mellors had a very successful year on the Continent with the new engine fitted in a rigid frame, however the factory reverted to single cam engines for 1937. Why they did not continue with the early DOHC engine is not clear but it did have a habit of breaking Oldham couplings in the vertical driveshaft and the race department was wasting most of its time on the fruitless Aspen rotary valve project. Australian Frank Musset acquired all of the engines, one of which eventually formed the basis of Sid Willis’ 250 twin cam which came fifth in the 1953 TT.
In the tightened financial situation after WW2 there was wasn’t much money for a works team, however Velocette won the junior world championship in 1949 with machines virtually identical to Stanley Woods’ 1939 TT junior winner. In 1949 Percy Goodman somehow found the money to build five special 250cc and 350cc twin cam engines based on the MK8 engine. Magnesium alloy was again used extensively to reduce weight. A special 5 speed gearbox was used for the first time to keep these engines in the power band. The new engines were eventually housed in a much modified frame that took some design queues from the Norton Featherbed. The new semi duplex frame had a lowered steering head, two near horizontal tubes connecting the bottom of the steering head to either side of the seat tube and another tube connecting the top of the steering head to the seat tube; this runs directly through the petrol tank. Initially fitted with telescopic forks the factory reverted to girder forks that had needle roller bearings and two-way hydraulic damping. Works riders said it was by far the best handling and most comfortable Velocette they ever rode. Velocette won the 1949 and 1950 350cc World championships with the new engine in a MK8 frame. The new frames were introduced for the 250s and 350s in 1951. Despite this success the cash-strapped factory ceased production of customer Mk8 KTTs in 1951, and stopped racing altogether after Percy Goodmand’s death in 1953.
Eldee Velocettes
The Eldee Special began life as a 1936 250cc MOV Velocette and was developed by Les Diener into a very successful Double Overhead Cam racer. Les added a Mondial style arrangement to drive the overhead cams, allowing it to rev to 9,000 rpm, and with a glass fibre fairing achieved 116 mph. Les racked up a number of wins until he had a major accident on a Manx Norton that finished his racing career. Keith Hamilton rebuilt the Eldee in 1981 after it was badly damaged in a fire. Keith reintroduced Les Diener to his Eldee and after Keith donated some Velocette parts Les decided to make a second DOHC Eldee. Fortunately, the original patterns were available and work began in 1987. Eldee 2 was a more modern machine incorporating a number of engineering improvements, Les took to the tracks again at the age of 68, on the Eldee2. The Eldee 2 was eventually acquired by Phil Price who has raced it successfully ever since. The Eldee 2 Velocette taught the team valuable lessons. The short stroke double overhead cam engine produced relatively more power than a normal KTT, a five or six speed gearbox was required to really use the power, and the power to weight ratio was critical. The original Eldee is now owned by Motorcycling Australia. The full story of the Eldee Velocettes appeared in OBA 13.