Glen's Flat Tracker

Like lots of XS owners, I have been fascinated with flat track racing and the bikes that make it such a wild sport. Websites like 650central are full of inspiration and after looking at lots of other people’s bikes I decided to do my own. 
My requirements were pretty broad:     

  • Stacks of low end torque
  • Ground clearance, brakes and suspension that would allow the bike to be thrown around the Great Ocean Road (very close to my house)
  • Fun to road ride for reasonable length of time
  • Enough noise to set off car alarms at wide open throttle 

The goal is to do as much as I can myself, and pay someone to do the critical welding, frame painting and wheel building. I started with a 447 engine I was originally built for drag racing. The current spec is shown below:

  • Uprated clutch with Halco springs
  • 840cc conversion (Modified Suzuki SP370 pistons in new liners with barrels and crank case openings modified to accept them). 1.5mm valve to piston clearance.
  • Bore increased from 75 to 85mm. 10:1 compression ratio.
  • Inlet and exhaust porting – designed by me and performed by professionals in the UK.
  • 2mm oversize stainless inlet and exhaust valves in new seats with titanium collets and retainers
  • Frank Trost street cam.
  • 36mm DellOrto pumper carbs (Ducati) with POD filters
  • Boyer ignition 

I bought a ratty 1980 SE for $2000 as my donor bike and fitted the new engine to it for a shakedown before stripping the bike. The motor pulls brilliantly but will need a better exhaust system and some dyno work to optimise the jetting. This is my first motorbike port design so no outlandish claims – I will see how it performs when tuned. 


Next step was to completely strip the donor bike and throw pretty much everything into boxes to be re-used or sold at a later date. Time to get medieval on its ass and grind off all the excess brackets I would not be requiring – very therapeutic but also a bit daunting.  The rear seat support was removed to make way for a tracker style seat. I paid lots of money for a new tracker style seat from the UK, only to decide it was not the right shape for me. Grab a fibreglass single seat from ebay and cut it to bits to give the shape I needed. 


I decided to ditch the perfectly serviceable SE tank in favour of an ebay 1974 tank – just to be different. Of course it is never straight forward, and this tank required dozens of hours of stripping, filling and sanding to be serviceable. The original tank mounts on the frame were ground off and new brackets welded to the frame to accept the new tank. This also required new steering stops, new rear mount boss etc. 


The cast wheels were not the look I wanted, so I dug up a standard XS front hub and drum rear hub and had these laced into new rims. I have gone for 18″x2.5″ rear rim and 19″x2.15″ front rim with wheel building by Graham Dawes in Geelong. Some new rubber from Road & River (Macadam 130/19 rear, and 100/19 front) and I had the makings of a tracker. 


The standard front forks are pretty awful and were junked. Lots of XS’rs have vastly improved the handling by uprating the standard forks, but I knew I wanted modern brakes, so a Yamaha Thundercat (early R6) front end was grafted on with taper roller bearings. Rear shocks are Hagon but their performance is yet to be evaluated and may not make the final cut. Top yoke (triple tree clamp) is the most expensive part on the bike! Billet CNC from Germany to suit the forks. 


Modern Brembo master cylinder and 4-pot callipers should pull this baby up pretty quickly! New fabricated brake mounts hold them to the forks, gripping standard drilled XS disks. This is still work in progress as the back of the callipers just clip the spokes. I may space them out a few mm or try some SV650 callipers. I would also like some after-market floating disks but I have already blown the budget and don’t have much space to mount the callipers. 


New KTM switchgear (the neatest, most durable stuff I have found), Boyer ignition, small 12V commercial spotlights as headlights and new fusebox form the basis of the new electrical system. Everything is being re-wired from scratch using good quality automotive connectors, and the bucket load of un-necessary 1970’s electrics are being ditched. 

The Next Steps

I sold some of the unused bits to fund the rest of the program!

  •  Exhaust system needed to be designed and fabricated. Twin high pipes are definitely the go. I will probably get some pre-bent pipe and tack-weld something together which can then be reproduced by a shop. Tuned for mid-range rpm.
  • Front brake issue needs to be resolved, and stainless lines made to length.
  • The front headlight is just a mock-up and needs to be fabricated from stainless.
  • External oil cooler being considered.
  • Battery mounting required. Small gell cell battery under the seat.
  • Paint/powdercoat the frame a gun-metal grey
  • Tank is painted in a basecoat of Absynth yellow. Yamaha black and white chequer will be run down the flat edges of the tank and rear of the seat. 

Still loads of work to do, including an obscene amount of sanding, painting and polishing. Inspiration from, Yam650 list and Terry Gliddon. The pictures below track the progress of Glen’s build.

All the hard work and patience has finally paid off with a great looking piece of machinery that goes well and has handling to match.  Congratulations Glen.