Posts Tagged ‘Mono’
During the summer of 2000 Perry Leask and I began speculating on the feasibility of building a lightweight supermono racer utilising a motocross engine. We argued that a machine producing 70bhp and weighing 100kg (0.7bhp per kilo) would compete favourably with the traditional Yamaha and BMW racers that produced 80bhp but weighed in at 130kg (0.61bhp per kilo).
Even Ducati’s Supermono, which at around £16,000 is the famous Italian marque’s state of the art single cylinder racer which produces 75bhp, weighs in at 135kg (0.55bhp per kilo). Aside from the obvious power to weight ratio there would be far greater advantages in handling, corner speed, braking, acceleration, aerodynamics and general efficiency. A smaller more efficient engine, breathing through a single carburettor would produce less unwanted heat, would require a smaller fuel load and suffer less paracitical losses from smaller water and oil pumps. It would require a smaller radiator and therefore less coolant. This would give further improvements to power to weight ratio and handling benefits when considering real race masses. It would also be slimmer to aid aerodynamics and lighter to require less substantial mountings.
Being more compact it could be positioned in the chassis to give more freedom to consider weight distribution, centre of gravity, chain alignment, ground clearance, the positioning of ancillaries and the passing of air ‘through the bike’. A lighter machine would run smaller wheels and tyres, require only a single front disc and be far more conservative with tyre wear. Less rotating mass both in the engine and wheel assemblies would result in a quicker steering bike with less inertia.The Late Nights Begin…
A Husqvarna engine was the obvious choice as we already had supermotard engines producing 67bhp in the confines of a dirt bike chassis and with exhaust designs compliant with stringent noise regulations. We had also built a deep knowledge of potential reliability problems from our off road experience, having recorded British Championship wins with Husqvarna in both Motocross and Enduro. We saw an opportunity to speed and control our movement into road racing, at the same time strengthen our position as Britain’s number one Husky tuning company. In September, we purchased a used Spondon TZ250 style chassis and the late nights began! We finalised engine position and delivered the chassis to Nu Trak components in Bolton to manufacture and heat treat an engine cradle and carry out minor frame modifications. We scrutinised the rear suspension geometry and made modifications to improve the linkage ratio progression curve.
Perry re worked a GSXR600 Ohlins rear shock, which we fitted along with an Ohlins steering damper. The upside down WP forks also received Perry’s attention being extensively re valved and re sprung, the stanchions titanium nitride coated and the Spondon adjustable triple clamps anodised. Turning to the engine, data acquisition from previous supermotard testing showed that the very basic lubrication system resulted in alarmingly high oil temperatures when run in a road race environment. We decided to drop the oil out of the engine into a heat exchanger to allow it to cool and deairate before being filtered and fed back to the oil pump. Given that pressure from the downstroke of the piston is used to exhaust oil from the crank area back to the gearbox (i.e. scavenge), great consideration of the position of oil ways and breathers was necessary. We chose a longer con rod, which gave a safer rod/stroke ratio and angulation that would assist reliability at sustained high revs and achieve an increased dwell around TDC*.*A short con rod which often benefits a dirt bike can accelerate the piston away from TDC too fast at high rpm, chasing away from the combustion charge too quickly. The relativity large cylinder bore that requires more time to complete combustion worsens this situation. Con rod length and rod/stroke ratio can define how an engine “feels” on the track more than performs on the dyno and selection is less than straightforward in the Husky’s case with the unusual offset bore. Previous motors built with longer con rods had proved less than successful, their deficiency attributed to a lesser acceleration given to the inlet charge, a problem countered by camshaft selection, valve timing and altered inlet length.Enter Steve Ruth
For big end longevity, we utilised a 41mm assembly in preference to the standard 30mm item. We re balanced the crankshaft to compensate for these modifications along with the larger 100mm piston, which took cylinder capacity to 600cc. We consider this engine size to be optimum having previously experimented with 577cc, 625cc and 633cc. A six speed TE enduro gearbox was chosen with first gear removed leaving neutral at the top, aiding neutral and start line gear selection. Our supermotard racers had suffered with clutch slip necessitating increased spring tension, which in turn led to pressure plate deformation. To alleviate this problem we manufactured a solid aluminium pressure plate and modified the crankcases to accept a hydraulic slave cylinder.
AC exhausts made a two into one exhaust system that was dimensionally a copy of a successful supermotard system made to fit our new application. To speed development we employed the use of our Pi Research data recorder. We fitted sensors to measure crankcase oil temperature, heat exchanger oil temperature, water temperature, exhaust gas temperature (EGT) engine speed, front wheel speed, gyro and g forces. Dave Carnell of D & M Racing had agreed to handle the team manager’s duties and suggested a rider, Steve Ruth. Steve is a very experienced mono campaigner, with four British Championship wins to his credit. We contacted Steve who drove down from his Suffolk home to view the project. Steve was impressed with the bike and agreed to a track test the before making a decision regarding the season. He was already sponsored for the European Championship on a Tigcraft BMW. The track debut took place at Brands Hatch on the 14 March 2001 in the hands of Andy Nichols. The outing was a complete success with the anticipated top speed of 125mph achieved.Off to Snetterton
The data logger showed the heat exchanger 25 degrees centigrade cooler than the oil in the engine and zero clutch slip. More surprising was the fact that Andy had lapped quicker on a totally new bike than he had ever done before in less than ten laps! Corner speeds looked equally impressive with 80mph around Paddock Hill bend an example. Our philosophy of “little, light and efficient” appeared to be working as the radiator donated from a tiny 400cc bike required substantial taping to achieve running temperature. Further endorsement was the fact the bike was returning a staggering 50mpg! A second test at Snetterton on March 27 was not as encouraging where a recorded top speed of only 125mph led us to believe we had an aerodynamic problem. Dyno testing pointed us to the fact that insufficient air was being delivered to the back of the carburettor. We had always been aware that a well-developed air box would increase engine performance significantly but we had decided that there was insufficient development time to explore that option.
We fitted two air ducts to direct air under the petrol tank. The next track test, again at Snetterton was four days later on the 31st this time with Steve Ruth aboard. We awaited his comments anxiously. Steve loved the bike, praising a strong engine and excellent handling. He stated that no other mono should out accelerate or out brake it. This time the bike recorded a more impressive top speed of 131mph, undoubtedly due in part to Steve’s riding ability, but the data logging showed better acceleration, presumably a result of the air intake modifications. What Perry had achieved with the handling of the bike was almost unbelievable. New racing projects are expected to take a season to develop, yet here we were with only 82 practice laps completed, talking to a four times British Champion who was struggling to criticise the handling. The motor was stripped and checked.Mallory Park
The small end bearing looked good this time, but the cylinder was very poor again. We used a cylinder replated by Aptec for the rebuild. With the first scheduled race being championship round one on May 6, we had set ourselves a near impossible task, to design, build and develop a prototype racer in eight months. However, we had completed the first part of the project and took our place at the first round of the UK Championship at Mallory Park. A disappointing eighth place in qualifying placed us on the third row of the grid. We analysed the recorded data and discussed Steve’s comment that he thought he felt the engine tighten on the back straight. The top speed was lower than that recorded on the test day the previous week despite the using the same gearing. The data logger suggested that no engine damage occurred by examining the EGT traces. We noted that a change in wind direction had turned a tail wind into a headwind on the back straight. We concluded that a gearing change was necessary. Gearing choice would prove to be critical throughout the year.
In the race, Steve made an excellent start to make second place by the first turn. A race long battle with Paul Thomas ensued and at the flag, Steve finished third beaten by a length of a wheel. The following day and round two was at Donington Park where we recorded another third, placing us second overall in the championship. Some minor jetting changes had made a significant improvement to performance; we had been unable to set the carburation accurately on the dyno without the ability to reproduce a 130mph headwind. This is a pitfall of not having a properly developed air box, resulting in carburation that varies albeit slightly with road speed. Before rebuilding the engine, we embarked on some exhaust testing on the dyno with spectacular results. We had originally chosen to run a single exhaust system (two into one) primarily because it fitted with our “little, light and efficient” philosophy. It was time to explore the gains from a two into two system and decide if they would justify the extra weight.Cadwell Park
Tony Cook from AC exhausts made a “dyno” system with provision to try a variety of dimensions for headers and silencer cans. Tony had been concerned that the two into one system would be very noisy when in fact it was so quiet we had even opened up the tailpipe after the test sessions. The two into two also seemed very quiet bearing in mind that the opposition had serious problems passing the noise test using a very similar system. Back to that keyword efficiency again. Using optimised header pipes and the silencer cans that would normally be used on a mono, we managed a significant gain in peak horsepower but with a big loss in the midrange. The peak numbers were good (75bhp) but not compensatory for the loss in midrange power. The “overrev” gains were too good, the engine still producing 70bhp at 10,000rpm. We felt that Steve would rev the motor too hard without the “natural rev limit” of the power tailing off at 9,500rpm.
We tried much smaller 2” exhaust cans and transformed the midrange deficit into an increase, with little loss at peak (74bhp) and with a defined tailing off at 9,500rpm. We settled on this configuration and the motor was rebuilt for rounds three and four at Cadwell Park. Another disappointing qualifying session placing us fifth on the grid resulted in another post session de briefing spent studying data logging traces and discussing gearing. Steve felt that he was in the wrong gear at just about every corner then showed his class by sketching a course map and indicating which gear he was using at each turn. The data logger verified the information and we set about exploring some “what if” scenarios with the help of a spreadsheet to calculate road speeds from engine speed and gearing combinations. A good decision resulted in Steve lapping over three and a half seconds quicker in the race! Steve had moved up to second when on lap five disaster struck. The crankcases split and our race was over.Time to go for the win
The budget had not stretched to a spare engine, so a frantic overnight rebuild took place and Steve took his place on the line the following day. Steve retired after one lap reporting a vibration. Cadwell Park is not a place to take any chances, so all members of the team respected his decision. With no points scored over the two days, we slipped to fifth in the championship. Subsequent stripping revealed nothing wrong with the motor, but what was done was done. Had Steve finished second in the race we would have moved into the championship lead. We were bitterly disappointed but greatly encouraged by the way Steve was reeling in the current British Champion Steve Marlow. Steve’s fastest lap of 1m 36.5 was only 0.8s off Marlow’s fastest lap of the weekend. At this point of the season, we were forced to review our championship philosophy.
Initially, we had targeted consistent podium finishes, as unreliability is so prevalent in supermono racing. Now that we had two non-finishes ourselves, the only thing we could do was to go all out to win races. Whilst on the subject of strategy, it is interesting to speculate if we had adhered to our original target of 70bhp/100kgs, would the crankcases have broken? It certainly taught us a lesson regarding the setting of goals and the need for proper discussion before they are modified or disregarded. We rebuilt the motor into new crankcases. Despite identifying the need to win races, we decided to lower the compression ratio slightly, run slightly less ignition advance and use a cable operated clutch to avoid welding and possibly weakening the new cases. Rounds five and six at Snetterton doubled up as the British rounds of the European Championship and we were relieved to hear that Steve had prioritised riding our bike in preference to his European mount. The season so far had been very disappointing for Team Hurst Racing.European Win
Qualifying saw Steve take third place on the grid, only 1.14s off pole. Torrential rain delayed the start of the race and Steve eventually took second place behind Steve Marlow in a wet race. Sunday saw dry conditions with Steve looking very sharp in morning warm up. The race was probably the best of the year with Marlow setting the pace, Steve sitting comfortably on his tail. We had observed that whenever Steve rode like this he was usually confident of passing, but reluctant to show his hand too soon. Mark Lawes added to the excitement when he joined the scrap with a few laps to go. As the leaders came into view for the last time around coram curve, Steve was in the lead, having dived past Marlow at the end of the back straight. He managed to hold on to the lead and took our first win in fine style, only 0.52s covering the first three places. Marlow did not take his place on the rostrum; we felt we had him on the ropes! The data logger showed a lap time for the final lap of 1m 15.26s, a new class lap record on a water-cooled supermono.
Mark Lawes had actually gone faster on the air-cooled 800cc Suzuki with 1m 14.56s! We were elated. The development of the bike over the last fifteen weeks could be quantified by the three visits to Snetterton and the top speeds recorded. 125mph, 131mph and now 140mph. A new bike had been taken from concept to European Championship race winner in less than a year, some learning curve! We had always assumed that our bike would be less competitive at a track like Snetterton, fast with its two long ‘stop and go’ straights. If we could win here, we could win anywhere. A rebuild with no changes and off to Pembrey in Wales for rounds seven and eight. Steve qualified in sixth place and the second wet race of the year saw us finish in a disappointing third place. Expectations had become so high that anything other than a win seemed a disaster.Castle Combe
We did identify that the use of a different section rear tyre had possibly upset the balance of the bike. Sunday’s race was dry and Steve made a fantastic run to the first turn, exiting in the lead! After a lap or so the race was stopped, allowing Adrian Stringer who had broken down on the sighting lap, to re join the race amid some controversy. The re start saw Steve grab second place exiting turn one and then to the delight of the entire pit lane (with half a dozen exceptions!) powered past Marlow on the main straight. Steve maintained the lead to record our second win of the season. It is worth mentioning that the Pami BMW of team James is effectively a works machine. BMW commissioned Pami to develop the 660cc for use on the Paris to Dakar rally. The 760cc version used by Marlow is reputed to produce 85bhp and is festooned with lightweight carbon fibre parts and is a result of at least five years development.
We never expected to see our racer out perform such a machine in a straight drag race. We had envisaged gaining an advantage through handling, braking and a superior power to weight ratio. With one round remaining the championship’s winner had been decided, we could no longer catch Marlow. We were determined to secure second place by winning the last round and therefore three of the last four. Qualifying at Castle Combe saw a drying track from a previous downpour. We were concerned that at Pembrey during the wet race the engine had run too cold. Consequently, we taped off more of the radiator than previously considered necessary. After seven laps, Steve pitted complaining of an engine noise. Something was obviously wrong and we returned to the paddock. By this point of the season, we were prepared with a spare engine, but it was a day’s work to change it over and we had three hours before the race. Perry and I started working, fast, very fast. We finished and warmed the bike up with about ten minutes to spare.
Data logging again supplied an explanation for the failure, showing water temperature increasing rapidly on the first lap to 100 degrees centigrade and then falling while oil temperature increased steadily over the eight laps also to 100 degrees centigrade. We concluded that either we had boiled the engine dry on the first lap through too much tape applied to the radiator or the radiator had sprung a leak, losing water. Steve had not noticed the temperature increase on the first lap and after that, there was insufficient water to work the temperature gauge. Our hard work was rewarded with the most impressive win of the season. From a lowly eight on the grid, due to the premature end to the qualifying session, Steve moved into third place at the end of the start straight. By the end of the lap, he had a three-second lead, six and a half seconds at the end of the next lap.
Steve used this enormous lead to best advantage allowing Adrian Stringer to get close, but not too close. He won the race and our season was over. We had won three of the last four rounds, recorded a win and a second in the two European rounds contested, set a class track record and finished second in the UK championship. After much deliberation, Perry and I decided not to take the mono project any further. We had proved what we had set out to and felt there was little benefit of contesting next year’s championship, no matter how tempting. We had gone from the team given little chance at the start of the year, with our “chainsaw”*, to the most professional team in the paddock, almost expected to win next year.
The project had been a colossal drain on HM Racing, especially in terms of time taken preparing the bike and could not be justified for another season. We had enjoyed the challenge and we had learned an enormous amount along the way. Technically, we had achieved 110% of our goal, as we had never envisaged our machine passing the PAMI BMW under power, on a straight. As a racing project, we must concede to only 90% success, as we did not win the championship. However, it is a prerequisite of building a new prototype racer that it be allowed three years to deliver and we had come desperately close in one hard but very satisfying season. Steve Smith
*Team James’ Steve Marlow had named our racer “the chainsaw” at the first round at Mallory Park, presumably due to Husqvarna’s reputation for garden machinery.