Building Our GT650R Race Bike
June 10th, 2008Converting a Comet GT650R into a race bike requires considerable work resulting in a machine that only loosely resembles the original machine.
Here at the shop we all had a chance to ride the Comet on the street to put a few miles on it before we began the process of conversion. Without exception we enjoyed riding this bike. She was dubbed “The Little Redhead” by one of the staff members and the name stuck.
Here she is dressed in the team ‘Hurry-Up Racing’ team colors. I guess a name change is in order.
The Central Roadracing Association (CRA) is where we will campaign our Comet GT650R. The CRA is the second oldest motorcycle racing club in the country. http://www.cra-mn.com/
Brainerd International Raceway (BIR) is in Baxter, MN, BIR and is the home track of the CRA. BIR is one of the fastest tracks in the USA. The prominent feature is the one mile long straight that doubles as a drag strip, followed by two high banked, high speed sweeping turn. The back section is a series of technical corners. http://www.brainerdraceway.com/
Every club or organization has a set of technical rules the machine must pass before it will be allowed on the track. Two of the more obvious ones have to do with the removal of parts. The lights, mirrors, stands, license plates, and accessories must all be removed. Critical items must be safety-wired to prevent loosening with vibration. All fill and drain plugs for oil and water, axle bolts, caliper bolts, etc. must be safety-wired as well. Less obvious to the non-racer is the need for body panels that incorporate a belly pan to hold 3 quarts of liquid in the event of a failure.
The Comet’s lower panels split at the bottom and have venting in low positions. It would not do for racing. We replaced all the body plastic with race plastic intended for a Ducati chassis. It did fit pretty well. The OEM mounting hardware weighed about 15 pounds. We saved considerable weight when it was replaced with light fabricated brackets.
Chassis work required replacement of the rear shock, the front suspension (stock springs, cartridges), and then the addition of fabricated shims to adjust spring preload. The stock rear sets were retained. Frame sliders were added to protect the bike when “the inevitable” happens. Stability at high speed is always a worry so a steering dampener is added to modulate any high speed wobble that may occur, and give the rider an immediate adjustment if necessary.
The front brakes were modified to use Tokico calipers. To make them fit we had the lower fork end brackets cut, fill-welded, and re-drilled to take a custom mounting plate to align them with the stock rotors. The brake lines were replaced with stainless steel lines, and the master cylinder replaced with an aftermarket part to feed the new calipers.
An exhaust system needed to be fabricated for the new bodywork and aftermarket muffler. Then the bike was taken to the Dyno for carburetor jetting and tuning.
Bridgestone race rubber was added to make this monster stick to the track. The original DOT tires could have been legally used in this racing class, but why take the chance. Further, the rear tire had picked up a sheet rock screw from the street riding we did to break in the engine before the conversion.
We’ll need to do some final adjusting and add the graphics before the first race day so stay posted for the first race report.
