The (Abridged) Story of My Scott Racer
In 1967 I bought my first Scott, a very nice TT Replica. I soon tried my hand at vintage racing and as, at that time there were many people still racing, there was enough for a "Vintage Standard" i.e. road going class up to 1930. Very soon I was finishing in the first three but this was to be a short-lived glory. As the entry was declining, the race was enlarged by including bikes up to 1951, which meant competing against Triumph 650 Thunderbirds with modern tuning parts.
I would not change the specification of the Replica, as it was very original, so it retained its 20" wheel rims and hand change. It was not possible to get race quality tyres 20" wheels, so a wet weekend race meeting at Cadwell Park saw me negotiating the right left adverse camber downhill bend combination called "The Gooseneck", chasing a 650 Triumph. I remember having one hand changing gear and the left hand holding a very light feeling handlebar as both wheels were sliding! I said out loud to myself "This is crazy, its not a case if you will crash it, only when and it deserves better". When I returned to the paddock, I put it on the trailer and resolved to build a racer from what spares I could obtain.
Goerge Silk found me a single down tube frame and I had a copy of the original long optional tank made by Ray Pettit.
The rest was fairly standard. The first problem was a crash due to the gearbox output bush seizing, even after I gave it a big clearance. The gearbox and outrigger final drive received careful attention and many detail modifications. The next problem was cranks, I must have broken about 6 sets and the case was patched up with body filler and expanded aluminium mesh. I decided that the engine would perform better if the inlet tract was bigger and so welded up where the flywheel runs under the inlet tract floor and lowered the floor. The flywheel was made a little smaller to clear. I had found that there was no steel available to me at that time to solve the crank breakage problem, so in 1977 I designed a compact four bearing crank conversion that is still used today. The cranks were complimented by a pair of titanium rods, the little ends of which were controlled within the pistons by spacing washers. I made some blind head aluminium barrels that had chrome plated bores, as I had in the 1970’s regularly reconditioned Racing Yamaha TZ barrels and had learned from this. The carb was an over bored Amal type 289 with twin floats and I made transfer port cover castings with higher flow capacity. At one meeting I started the bike but, unknown to me, there had been a leak of water into the crank chamber. The engine fires instantly on the LH pot and the RH transferred up the water into the cylinder head and tried to compress it. The result was that the crankcase was broken across the main bearing and was scrap. I had put a lot of work into modifying this case, so this was a disappointment. I consulted a friend, Tony Pacey, who is a master patternmaker. Tony made me patterns for a new case that was of original external appearance, but was strengthened in many details and incorporated the larger inlet tracts as standard. The cases were made from top quality high strength aluminium alloy and heat-treated. I studied the problem of brakes and made new brakes to original appearance with cooling muffs and with an unusual operating and adjustment system.
The handling of the bike had always been difficult and a ride on Clive Waye’s racer proved just how bad it was by comparison. The class I had been competing in was for bikes up to Dec 1930 and so the Scott had to be of the type, which used a non-detachable cylinder head. As the entries were declining, the VMCC racing section decided to extend the period eligibility up to 1934. At this date Scotts had a detachable head and they had sold a few four speed gearboxes, most of which were returned to be exchanged for three speed boxes as they had significant design faults. Tony Pacey again made patterns for a high compression version of the detachable cylinder head, a matching aluminium barrel to have chromed bores and the four speed gearbox casings. The gearbox design faults were eliminated as far as possible to achieve a workable gearbox and high compression heads were made.
I was excluded from a race meeting at Oulton Park because the exhaust was too loud, so I fitted a modest resonant exhaust system that made the bike quiet and gave approximately another five bhp when used with a 38mm TT type carb.
Ignition reliability and drive durability had been a problem, so a belt drive to the magneto was arranged to drive from a pulley on the clutch drum, instead of the "Sprint Special" type chain drive to the magneto from the clutch drum. A test rig was made to check magneto output and more importantly, the sustained accuracy of the spark timing. The results showed that where I had imagined that the power was limited by the engine breathing efficiency, it was, in fact, being limited by the magneto spark losing its timing in a similar way to a four stroke engine having "Valve bounce". I designed and made a conversion to a BTH magneto using PVL components which brought further improvements.
When Tony Harris started to make his new BTH magnetos, I was happy to try this with great success.
In 2003 I crashed heavily at a race meeting in Anglesey and because of injuries was unable to race. Tony Harris suggested that I contact New Zealander Paul Dobbs to see if he wanted to race the bike. Paul had never raced such an old rigid bike before and initially, he was very unhappy with the handling. He suggested that there was not enough weight on the front wheel and so the seat and bars were re arranged. Paul pronounced himself satisfied and remarked that he had never experienced such a high degree of feedback from a bike and that this gave him great confidence to use it hard gaining spectacular results.
As an engineer who has spent his life designing and building special machinery, this bike has been a very stimulating project. The Scott would not be the first choice if success were the absolute goal. There is a bigger hill to climb than, for instance if you pick a camshaft Norton. If the reader is concerned at the amount of special engineering that has gone into this bike, then I assure you that almost all of the other successful historic race bikes are highly special inside and use alcohol fuel. The Scott uses unleaded pump fuel! The development has taught us which modifications bring the optimum results, first as regards durability and reliability and also as regards gaining power and smoothness without sacrificing the high torque characteristics of the Scott engine.
Here are a List of Modifications (that i can remember!) with the reasons for them :
Frame (1) Lower frame rails removed To give cornering clearance
Frame (2) Lightweight frame made To reduce weight and increase stiffness
Forks Modify friction dampers To enhance damping
Forks Cast silicone rubber in spring To enhance damping
Forks Phosphate treat To protect from corrosion but still see any cracks
Brakes front (1) Fit two Webb drums To improve braking
Brakes front (2) Make new better copies To improve braking
Brakes front (2) Redesign brake plate To improve braking
Brakes front Twin brake cable compensator To improve braking
Brakes rear Make new hub and brake To improve braking and accommodate sprocket changes
Petrol tank (1) Copy of long sprint tank To suit frame and personal preference
Petrol tank (2) Lightweight alloy tank To suit new frame and enclose oil tank etc
Petrol tank Twin big feeds To deliver 1000 ml / min at carb
Carb (1) Amal Type 289 overbored To achieve better results
Carb (2) 38mm TT type carb To achieve better results
Lubrication 3 port drippers To feed main bearings and primary chain
Lubrication Non return valves To feed main bearings
Lubrication Petroil to engine 5% Castrol R 40 in fuel
Cranks Four bearing crank Frequent breakages
Gearbox output bush Needle roller bearing Seizures and high friction
Clutch release Twin cam design To give lighter and smoother clutch action
Gearbox output Oilseal added To prevent oil contaminating clutch
Final drive outrigger Self aligning bearing To eliminate inaccuracies causing friction
Final drive outrigger Snail cam location To prevent outrigger being pulled to rear, (seizures)
Gearbox 3 speed Non standard ratios Ratios to suit engine output for racing
Gearbox 3 speed Internal lubrication mods To reduce friction and wear
Gearbox Large undertray clamp plate To get maximum clamping effect to reduce creep
Gearbox 4 speed Redesign and make gearbox To have eligible Scott type 4 speed gearbox
Gearbox undertray Reinforced To prevent cracking in stressed areas
Clutch Thicker stronger plain plates To reduce wear on dogs and warping for cleaner action
Clutch Reinforced pressure plate To reduce dishing and loss of efficiency
Clutch Better friction plates To transmit more power even if oil coated
Clutch Stronger clutch springs To cope with increased power output
Clutch Fit belt pulley to clutch drum To replace troublesome chain drive to magneto
Magneto (1) Have special magnetos wound To try to achieve better efficiency
Magneto (2) Electronic mag conversion To achieve reliable sparks at high revs
Magneto (3) Harris / BTH magneto To have optimum ignition
Magneto Belt pulley and belt For smooth reliable drive
Crankcase (1) Mods to inlet tract To improve breathing
Crankcase (2) New case To incorporate internally all improvements learned
Main bearings Ball bearings More durable and efficient
Crankcase seals Synthetic modern seals Preferred design
Crankcase Upgraded clamping to frame Engine case used as stressed frame member
Crankcase Aperture in front To aid cooling inside case and give access to chain
Crankcase 4 bearing crank Detail mods to use 4 bearing crank
Barrel (1) Blind head iron modified To enhance output
Barrel (2) Blind head alloy To enhance output
Barrel (3) Detachable head alloy To enhance output
Head High compression To enhance output
Con Rods Titanium beam section To reduce bearing loads
Big end Bearing cages To control rollers
Small End Located in piston with spacers To keep rod running squarely on big end rollers
Pistons Lightweight ported To give access to locate little end and upgrade transfer.
Transfer covers High flow covers To transfer more charge efficiently
Exhaust Resonant exhaust To enhance output without loss of low rev torque
Flywheel Graduated in degrees For quick and accurate setting of ignition timing
Flywheel 22 T primary drive sprocket To speed up gearbox to reduce box and clutch loadings
Primary drive Fit brush oiler To ensure long life for primary chain