The new Top Fuel Bike power unit will be a fuel injected, supercharged, in line 3 cylinder design with a capacity close to the construction regulations limit. This will be coupled to a “slider” clutch and 2 speed gearbox, driving a 14” wide rear slick.
So why a 3 cylinder engine? I could elucidate about the better power potential, lower frictional losses and more compact nature of this arrangement compared to conventional 4 cylinder engines…but really the selection of the 3 cylinder configuration boils down to two things:
I wanted to do something different, rather than just build another 4 cylinder TFB clone.
I have always liked 3 cylinder machines – I had several Triumph T150 Tridents as a “boy” (I still have my old T150 café racer, which has been in boxes for around 25 years), my first drag bike was based on a Laverda Mirage engine; even my tractor had a 3 cylinder engine (MF35).
All the above is still true, but if I had been aware of some of the challenges involved at the inception, maybe the engine configuration selection would have been different (but then again, maybe not).
I have to admit that I was blissfully unaware on the inherent vibration issues associated with in line 3 cylinder engines. My old T150s always seemed pretty smooth (coming from a background of British twin cylinder motorcycles), although the café racer with the stroked engine and steel rods was a bit lumpy. Modern 3 cylinder engines all incorporate balance shafts to cancel out the inherent vibration. The new motor won’t have any sort of balance shaft and will have BIG pistons; on the other hand, it won’t be doing any long distance events – just need to hang on for under 6 seconds! (hopefully).
The other major issue is the ignition solution. There just isn’t a high power 3 cylinder magneto ignition available.
I am fully aware that I might spend the rest of my life (or at least until I run out of cash) trying to get the motor reliable….luckily this falls into the category I consider to be fun!
The motor is basically a de-stroked Triumph Rocket lll with a capacity of 1690cc. Four valves and two plugs per cylinder with dual overhead camshafts with end belt drive.
The bottom end comprises billet
aluminium crankcases with a nitrided
EN40B crankshaft and forged
aluminium con rods (Bill Miller 500 series).
The main bearings are the 60mm BMW type
with 2.1” journal small block Chevy big ends. The design
incorporates the facilty to run outboard roller bearings at
both ends of the crank, should this be required.
The con rods connect to forged,
coated fuel pistons (BME) using
0.990” gudgeon (wrist) pins.
Billet aluminium cylinder block with ductile liners
and piston skirt oilers.
Billet aluminium cylinder head. 4 valves per cylinder -
valve gear supplied by APE. Twin plug. End driven camshafts.
The lubrication system is dry sump using a 4 stage
AVIAID oil pump (1 pressure, 2 crankcase scavenge,
1 cylinder head scavenge). The pressure stage
delivers around 3gpm per 1000rpm. The fuel pump
is driven off the end of the oil pump.
2.1 HPS dragbike blower.
The fuel system will initially utilise an Enderle 1100 fuel pump,
with a PBR (i.e. home made) barrel valve and DJE BDK valve.
Fuel nozzles will be a PBR design.
Twin SM+ (10A) magneto generators
energising monster black nitro coils which
deliver the sparks to a remote distributor
driven off the end of each camshaft.
Each magneto generator is driven via a
pneumatically operated mechanical advance/retard unit.
90mm wide Gates GT carbon belt.
PBR “slider” clutch.
The friction & steel plates, facings and arms were supplied by Boninfante.
The “multistage” capability is provided by a PBR direct acting “air” cylinder design.
B&J 2 speed; triple sprag.
Hawaya Racing 14” wide Top Fuel Bike wheel (sidedrive/beadlock).
Tubular chassis (4130 CrMo), fabricated by Al Smith. 98-100" wheelbase. 45 degree rake. Crankshaft 56" from rear wheel axle.