GRT F3A Oriental eater
There must be easier ways to make your race bike go faster than designing and building your own engine. But the Greytown Racing Team in New Zealand were up for the challenge – they made the frame and most everything else, too. Long-time racer Doug Fairbrother and fellow Greytown resident Peter Thompson made plans to create a competitive Formula 3 race bike using a large capacity 500cc single cylinder motor.
The project began in November 1985 and after two years designing and developing a brand new engine in their own chassis, the GRT F3A/500 was good to go in December 1987, coined the ‘Oriental Eater’. But it was a long story to get there with more twists and unexpected design turns than your favourite back road. Fairbrother takes up the story, “We decided what we wanted and we just went ahead and hand-made it; we wanted to make a modern day Manx Norton. Originally my mate
Peter wanted to make a crankshaft and he said, ‘Why don't we make the whole motorbike?’ And that's what happened, as a single cylinder engine is easier, cheaper and simpler to build.” They had much to learn!
Originally from Zimbabwe, the legendary Colin Lyster has been identified as the father of aerofoils fitted to race bikes while he was living in the UK during the late 1960s. He emigrated to New Zealand in 1975. Lyster helped numerous competitors worldwide with their car, speedway and motorcycle projects through the years, including the 999cc
Denco V-twin motor which John Britten used in his Aero-d-One composite monocoque framed racer. A mechanical design engineer, Peter Thompson worked with Lyster at the Cawthron Institute in Nelson, New Zealand's largest independent science organisation.
The Powerplant
Without the aid of modern computer design, the engineering challenges faced making a motor today are almost unthinkable. Thompson explains, “I made the (double overhead) cams, the conrod, the crankshaft (on a 1920s era lathe), the piston, but we bought in the valves. We made these parts as they were expensive in those days, a conrod was $500 so we couldn’t afford that, so I had to make them.” The powerplant has a plain bearing crankshaft, with a plain bearing on the big-end side and a roller bearing on the primary drive side. “We had to cut our own primary drive gear for the crankshaft to match whatever clutch gear we were using to get the centre space out. There is no balancer, so with a big single – you’d know it was running!” The engine cases were cast from patterns designed by
Thompson. The motor was handmade with the exception of the gearbox, and clutch, which came from an XS650 Yamaha.
“Initially we were sharing the same crankcase, gearbox castings and barrel castings as the first Britten V Twin”, Thompson recalls, “This bike originally had an XS650 gearbox in it that Rob Selby had selected, he worked for John Britten. We recognised that Rob’s original setup was limited, which is easy with hindsight. You have to remember that it was in the mid '80s and there wasn’t the plethora of equipment available that there was later on. Subsequently I took all of that off and designed a new gearbox using a TZ750 cluster and clutch, so I made new patterns for that.” Fairbrother adds, “The current six speed gearbox came from a sidecar which is a Dyson from Scotland that was used in a TZ750. The dry clutch is handmade, with covers off a TZ750. It now has a Cosworth piston with Cosworth profiles. Peter Thompson manufactured the conrods and flywheel. It has a single plug head with four valves, and the shims are under the buckets.” The dry sump single features toothed belt drive to both camshafts, direct off the crankshaft, with an idler roller to take up the slack. A home-made alloy cover plate was cast with large GRT 500 lettering, although this was later replaced by very small 'covers' which left the cam drive system mostly open to the elements. Dominating the right hand side of the motor are external oil lines. Oil is pumped from a separate oil tank, through a filter and into the engine by a hand-made pump running off the end of the exhaust camshaft, then out of the sump and back into the tank by a modified Hillman Hunter oil pump running off the end of the crankshaft. The pump on the inlet camshaft is a fuel pump that was being used to see if fuel injection was feasible.
Fuelling
The GRT 500 initially started life as a 90mm bore x 78mm stroke 500cc engine with electronic ignition and a mechanical fuel injection system, which caused numerous teething problems for the Greytown Racing Team. The original methanolburner had an extremely high 14:1 compression ratio. The engine was then fitted with a downdraft 38mm Amal MkII carburettor from a Jawa 4-valve speedway bike, onto which Thompson fitted a
remote float to reduce the vibration since the engine wasn’t balanced. The motor was canted forward a high 45 degrees from vertical to also help the fuel inlet flow. Typically, Thompson also cast the throttle body casings.
But with no balancer shaft the continuing heavy vibration from the large single piston spinning up to its 8,500 redline caused major fuelling issues. “Or we thought that was the problem, due to the angle of the carburettor and having to have a remote float on it,” Fairbrother says. “The bike initially had a carburettor off a speedway bike that ran on alcohol, which we changed to run on petrol, as we initially intended to take the bike to the Isle of Man to race in the Singles class. The engine is rubber mounted but it still shakes things about. We electronically fuel injected it when we changed the capacity from 500 to 600cc and changed it from a five to a six speed gearbox, with a dry clutch. “Getting the carburettor to run properly was problematic and the vibration killed it, as the fuel was frothing.” The team however faced larger issues with frame cracking, which occurred while they were busy sorting out balance factors and engine mounting configurations. The net result was a heavily braced frame and rubber mounting everything.
Chassis Challenges
Doug made the frame while Peter built the engine. The pair designed the frame with wheelbase and steering angle dimensions close to a Yamaha TZ chassis. Laying the engine well forward also allowed the motor to be underslung on the frame. Thompson continues, “We were initially going to use the RZ350 frame, however we decided that we could do a better job building a frame ourselves. The frame was our own design and people used to ask us if it was a Ducati frame, but we'd figured out what attributes we wanted the frame to have ourselves. “The frame was similar to a Ducati, there was nothing revolutionary about it, we just tried to join up the steering head to the swingarm and straight line the tube. Originally we had a shock absorber underneath the motor.”
The 42mm Marzocchi M1R forks feature air adjustability, with rebound adjustment on the right and compression on the left fork. Marzocchi triple clamps keep the front end together while a pair of four-way spring preload adjustable Koni shocks adorn the rear, with rebound damping adjusters at the top. Girling shocks featured on the original machine. To slow the GRT 500/600 is a single four-piston AP front calliper acting on a machined-down Ford V8 flywheel for the front brake disc, and a two-pot Lockheed caliper at the rear. Very Bert Munro!
Both calipers are hung on Greytown Racing Team-made brackets, as are the footrests and levers, and the triangulated swingarm. Working on a short 1340mm wheelbase, the Dymag rims are 18 inch diameter x 2.5" on the front and 18" x 3.5" on the back. Weight is thought to be less than 110kg.
Early Electronics
Peter Thompson explains the vast array of issues which still had to be conquered before the new engine could run properly; especially in the very early days of electronic ignition and before home computers emerged to help creative people develop their own systems. “We had a similar electronic ignition system to what Britten had on his bike which was a simple chainsaw magneto initially. We then went to the electronic Lucas system that’s on now, although we had a Boyer Bransden ignition system on it at one stage.” With no dyno available the low
budget project relied solely on old seat-of-the-pants tuning adjustments. Mark Robotham developed the electronics and built the circuit board. Thompson required two adjuster knobs for fuel mixture settings, one for enrichment and one for lean.
This allowed the team to continue road testing where they set the engine to a fixed throttle position and then made the necessary fuelling adjustments. “There was no ignition advance at that stage – we had provision for six more sensors, barometric pressure, air temperature and then any others you wanted, however we just used throttle position and engine speed. We didn’t use the other sensors at that point. We could burn eproms and flash the information onto that and get the information down to a few hundred revs, and the engine would respond to that.”
First Start-up
The GRT 500 fired up straight away and sounded pretty loud due to the large megaphone. After so much effort, it was a moment in time to hear the new engine running, yet there were many teething issues still to resolve within the engine.
Thompson continues, “When it first fired up I was just floating off the ground about six inches – it's something that very few people have experienced, we had worked on it for so long. It ran and it held the engine oil! I had done a bit of engine building with Colin Lyster so I knew what we were getting
into.” With massive hurdles ahead, most of their testing was performed on country roads around the back of Greytown – where they broke numerous parts. And, the Police were on board too. Peter again, “We used to do all our testing out at Woodside Road near the train station because the local constabulary suggested we test there as there were only two houses out there then, now there is a whole settlement.”
Their unique engine starting methods may have been questionable as they bolted the front forks onto the back of a Leyland van and towed the bike along the road until it started up – with the fuel tank and oil tank sitting in a tin. Thompson describes how to make a travelling bomb. “The tank is four or five litres, just enough for a short race. The first frame we designed – we had an old van and we designed a mount for the forks (a carrier) in the back of the van. This allowed me to sit in the back of the van with the fuel tank also in the back of the van while we tried to fire the bike up, and have a guy observing, and then using the forks bolted the bike to the van. The idea was to have a dry sump with an underslung tank. We had the first one welded up and Doug took it out to Woodside Road with strops holding the tank in place, and the strops went through the exhaust pipe and burnt, so it was like launching a bomb! It did stay together but that was one of those hilarious things. We heard it crunching along the ground.” It probably took another year from that point to get it on the track. There were oiling systems to sort out as the oil drains from the head – are we getting sufficient oil feed to the head? And we had to start thinking about camshaft profiles. “We went from dry sump to wet sump, mechanical fuel injected to carburettor to our own electronic fuel injection which is on there now, we were developing that in 1988. That was ahead of its time.” Without a dyno for an accurate measurement, a healthy 60hp at 9000rpm for the 500cc version was the figure bandied about at the time.
Let's go Racing
The Greytown Racing Team rolled out their all-new GRT 500 on December 19, 1987, the same day as the famous Britten Aero ‘d One was at Manfeild. While the bike was all-new, Doug hadn’t road raced for ten years. He still managed to perform some memorable wheelies off the line and his use of the grass verges was generous as he proved reluctant to back off for some corners. The GRT 500 also caused quite a stir amongst the crowd including some overseas mechanics who couldn’t believe that a race bike could be built by just two people on a shoestring budget.
Thompson expands, “We had a cam belt breakage which was quite common in those days, using the old trapezoidal profile cambelt. If you didn’t have the tension perfectly right it would grow long enough to over-tension the belt, and it would break the belt. It took us a while to figure that out. We got some practice laps in and I think Doug went out in the first race where it broke a belt, which became an ongoing issue.” The gearbox caused a few issues, and surprisingly the oil didn’t get hot enough to permit maximum revs – with the engine running
cooler on methanol. The front brakes were too aggressive necessitating a smaller master cylinder, and the fork springs proved too firm.
Next up was the toughest race track in New Zealand for a second shake-down of the Formula3 bike, Wanganui's bumpy Cemetery Circuit on Boxing Day 1987, a two-day event that year with the usual large crowds. Thompson again, “The second meeting we went to was Wanganui, and the first day it was wet so we changed the bike to wet tyres – and it broke a cam belt. We took the head off and Doug took the valves around to Nod Hartnel at Wanganui Aero Works and straightened the valves there, he then spent the night lapping them in. In the meantime I got in the car and drove all the way back to the workshop in Greytown (a 380km round trip) and made some new oil pump components as they had been damaged when the camshaft locked up. I worked through the night, got a couple of hours sleep and was on the road again at 3:00am in the morning to drive back to Wanganui. “When I arrived, Doug had the head back together, and I remember just finishing the final timing on the camshaft as the call went out to the riders to get the bikes to the dummy grid, which we made it for and completed the race. Doug confirms, “We had so many things happen along the way it's hard to remember. Then we went down to the South Island straight after that. We had to make some more valves and then we raced it at Levels, Teretonga, and at Ruapuna.”
Final Modifications
Over the ensuing years the GRT 500 became a 600, a six-speed transmission replaced the five-speed unit, alcohol fuel was changed to petrol, the fuelling system was changed no less than three times, and all manner of other mechanical and chassis components were swapped, altered, re-mastered, re-engineered or just plain biffed. In 1994 they were planning to take the GRT 600 to the Isle of Man, however Doug didn’t go because they couldn’t get the fuel injection to work properly. Peter again, “We converted it to petrol and I cast a new barrel with bigger fins, and I welded the fins onto the head. It ran like that up to the Paeroa event in 1995, by which stage we had fitted an alternator to it and we were running a dead-loss fuel system, as in those days most fuel injector systems were using car fuel pumps and they take a bit of power.”
“We came third in one of the BEARS classes one year,” Fairbrother says. “They used to have Pukekohe, Manfeild and Ruapuna, however I never won a race on it. The last time we raced it was at Paeroa, so it would have been 1995, because we had changed it to a 600 by then. It was pretty good and was going to be competitive, it was just the time and the money, and then slowly things caught up with it. It went alright at Paeroa, however we did a big end there that damaged the con rod, and the bike hasn’t run since then. When we pulled it down we found that the cams hadn’t been hardened enough, so we need stronger cams and we had also decided to change to a stronger style of timing belt. Between us we would have spent hundreds, maybe thousands of hours on this bike, probably more than a person doing an apprenticeship!”
Thompson reflects, “If we’d had a big Lotto win we'd start from scratch again taking lessons from our experience building this bike. The trouble with this project was that it evolved and we were stuck with original positions, and you don’t know whether to start again or to keep going. It was like Grandfather’s axe; we started changing things, and nothing now remains the same compared to the original engine. It’s actually a 595cc with a 96mm bore by 70mm stroke I think.”
While the GRT 600 didn't set the world on fire with results it was an incredible achievement. The effort and time involved is difficult to imagine, much of it in their spare time, and it certainly added to a growing NZ knowledge pool about self -designed and built racing machinery. No one can take that gutsy step away from Doug Fairbrother and Peter Thompson, ever.