[Kartbuilding] frame material

Stephen Burke sburke at burkesys.com
Sun Sep 13 23:22:46 IST 2009

Hi Oscar,

Thanks for the email and pictures. I added them to the kartbuilding.net 
gallery, as they looked really well. You have the kart finished 
excellent, with all the details taken care of. Its always nice seeing 
different designs, and also peoples feedback on the design.

A couple of things I really like:
# Rack and Pinion steering. Some people are against this and like to 
only have 1/2 turn of the steering wheel. I think its much easier on the 
driver to have 1 turn of the steering wheel using a rack and pinion.
# Transmission. I really like the jack shaft. Was this something you 
made-up yourself? I remember searching very hard to try and get a large 
enough sprocket to do without a jack shaft. It does complicate the 
design having two chains, but done correctly, it makes things much 
easier, and allows for lots of tuning afterwards. Your getting lots of 
revs out of that engine. Typically I think them engines only do 4000 
rpm, so if your getting 6800, I'm sure it goes like something else.
# The wheels & tyres. They do look nice and make the kart look really 
well. I say they cost a bit of money.

Its nice seeing a chassis made from square tubing, and your chassis 
looks really well. It can be difficult to use round tube for the main 
chassis, and in many cases requires a pipe bender. Your design and 
layout makes me think twice about using square tubing. It makes things 
much easier. You definately put a lot of effort into the upper and lower 
frame sections. It would be nice to see the effect on cornering. Using a 
live rear axle is indeed, much different to having only 1 rear wheel 
driving. Of course using a differential would be the best way, however 
its weight and complexity can out weigh the benefits.

Glad to hear your back moving around with the replacement knee. I hear 
the knee operation can be quite difficult and not as straight forward as 
a hip operation for example.
Well done again, in getting the kart made, and to a brilliant finish also.

Talk to you again.
Best of luck,

On 10/09/2009 18:46, Oscar Forand wrote:
> Steven,
>           My replacement knee is sure not a duplicate for the 
> original, but I just completed my newest race kart that incorporated a 
> lot a ideas I learned from your site.Pictures are attached, but here 
> are some of the details.  Maximum frame width - 26". Wheel base -  
> 44". Maximum width (rear wheels)  - 51".  Height to top of roll cage - 
> 50".  It became obvious real quick during construction that the roll 
> cage was going to make the frame to stiff.  Jpg 2 looks down where the 
> upper frame and roll cage are joined to the lower frame through a 3/4" 
> bolt pivot point.  The frame was still to stiff to flex much, so the 
> lower frame crossmember in front of the seat was also removed 
> providing plenty of lower frame flex.  To keep the lower frame 
> flexible, the small rack and pinion steering box is attached to a 
> dropped section of the upper frame, and the foot pan in front of the 
> steering box is is equipped with rubber bushings underneath to allow 
> the upper and lower frame sections to move independantly.  The front 
> spindles are Azusa kids kart types that have been flipped 180 and the 
> original steering arms cut off. New steering arms were fabricated with 
> Ackerman angle built in.  Castor and camber are zero.  The 1-1/4" rear 
> cromemoly hollow steel axle is fitted with a hydraulic disk brake 
> system and it works great!  You can see the dual chain drive through 
> the jack shaft.  By changing the input or output or both gears on the 
> jack shaft the the engine RPM can be set for maximum @ the end of the 
> longest straight.  I moved to jack shaft to a location behind the axle 
> to lengthen the drive chains to give the links more time to cool and 
> cut down on chain kinking. This seems to be working good.  The engine 
> is mounted on a 1/2" aluminum plate that has 4 slotted 3/8" bolt holes 
> as does the jackshaft mounting plate.  This allows the jackshaft and 
> engine to be quickly moved to tension the chains. The engine has a lot 
> of work done to it!  Originally a 6.5 HP Honda 4 stroke, it now makes 
> 16 HP @ 6800 RPM!  It has 12.5:1 compression and must run on 114 
> octane off road gas.  It has a cam with 230 degrees duration, uses a 
> Mikuni 24mm motorcycle carb, and a centrifugal clutch the engages @ 
> 3000 rpm.  The aluminum flywheel used in this motor makes acceleration 
> of this kart scary!   I still learning how to drive it, cause right 
> now it's easy to over drive the track we have with this kart. The 
> solid rear axle definitely requires a different driving style than the 
> one wheel drive karts!  The steering in the older karts was about a 
> half a turn lock to lock, this one is a full turn.  Also seeing how it 
> drives, if I was going to build another one, I think I would keep the 
> wheel base @ 48"  to reduce how quick it reacts to steering input.
> Oscar Forand
> On Tue, May 13, 2008 at 6:59 PM, Stephen Burke wrote:
>     Hi Oscar,
>     I'll be interested in seeing the new setup fully completed. Keep
>     up the good work. Im sure you'll be up and about in no time.
>     Best of Luck,
>     -steve
>     Oscar Forand wrote:
>         Steve,
>                The old karts I built were left wheel drive only
>         (because all the others were) and we have to race clockwise to
>         load the left rear in the corners or there is a real traction
>         problem!  Corners are normally taken in a 4 wheel drift going
>         to full throttle about half way through the corner.  Remember
>         we're running relatively small engines that do not have the
>         power or torque to just spin the drive wheel by applying
>         throttle once your moving.  There were no problems with
>         handling on the straights. This new one is setup for a live
>         axle incorporating a lot of things I learned from your sight
>         ,like the flexible frame, Ackerman steering angle, etc:  
>          Knee operation is done, and rehab is tough, so it'll be some
>         time before I'm working in my shop again.

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