BUILDING A CYCLEKART
BUILDING A CYCLEKART
BUILD SERIES no. 9: Redemption
GN REDEMPTION
Moving on from the Peugeot’s spa weekend, next up was the GN.
The GN has had a troubled life. Some adventurous decisions by its builder set it up for a series of trials and tribulations. An over ambitious double chain rear drive scheme “ate” the back of the chassis in the initial Gordon Bennett which then had to be cut off leading to a grafted on quarter elliptic sprung rear end that proved to be viciously evil to drive over rough ground. At the front, a death defying attempt at wire and bobbin steering had to be replaced and its awkward residual geometry was such that this ended up becoming a sand rail style rack and pinion unit. The effect of these two patches was that the long wheel base got even longer and with that came severe understeer which in an unfortunate instant would flip to severe oversteer (unintended rear wheel steering)! The bright spot was a really sweet engine and marvelous 7” driven MaxTorque drive unit (replacing the double chain concoction). Things were gradually improved with tweaks here and there but the car remained laced with vices and only a few hardy souls were risked behind the wheel.
This re-build season seemed like the time to address those vices. Things weren’t all bad, just a little off. A heavy wall “H” frame was welded onto the chassis at the rear to reinforce things (and keep them more predictable). The frame extends back under the springs dramatically reducing the rebound swing of the rear axle. The motor block no longer pitches forward and the ball joint mounting at its front/ center has been improved. All this moved the rear axle back slightly but the front the axle was also moved back keeping the wheelbase about the same. Moving the front axle back improved the tie rod geometry and in conjunction with the rear axle moving back eased the driver laden car’s balance a bit forward. All in all the GN drives like a dream now. The car was also converted to one wheel drive but with the option of easily reverting to two wheel drive for mud (Winter Tests).
Tear it down, build it up.
“H” frame in place. This reinforcing frame was welded to the existing frame and replaced the bolted on spring risers. The motor block is flipped upside down in this shot. You can see the friction damper (disks from Speedway and heavy washers from McMasterCarr). The “dog bone” is a pair of heim joints. The motor block pivot is also a heim joint (1/2”).
This shot of the motor block (1 1/2” plywood lamination) shows the drive arrangement. The old #35 sprockets are still on there but the general arrangement remained the same. I’ve said it before but I will say it again, I really like the MaxTorque unit. Second shot shows the revised steering rack location. A thick mounting plate moved it slightly forward and up. Bump steer is now almost imperceptible. The tie rods are steel with brass covers. The rake of the steering column came down slightly. This car uses shortened Azusa arms to quicken the steering. This offsets the rack.
The first generation of this car weighed 238#, the second 249# and now with the heavy wall “H” frame, heavy chain, etc., this car weighs 264#. The robust motor and 7” driven more than offset the weight. The car is fast and drives like a dream. Redemption.
We’ll see how she races next year!
Miller 1, Miller 2, the Maserati and the scuffed up Fiat are also presently under the knife. Updates on those projects coming soon. The shattered Austro-Daimler and battered Panhard are patiently waiting for attention.
Thursday, October 27, 2011