DIR Return Create A Forum - Home
---------------------------------------------------------
CycleKarts GB
HTML https://cyclekartsgb.createaforum.com
---------------------------------------------------------
*****************************************************
DIR Return to: Build journals
*****************************************************
#Post#: 12171--------------------------------------------------
1925 GN Cognac Special
By: jon.pearce Date: December 20, 2024, 11:12 am
---------------------------------------------------------
Hi all,
Just about to start posting my "Small Cognac" build journal on
here !
To begin, I have attached a photo of the inspiration car and a
photo of the current build !
#Post#: 12172--------------------------------------------------
Re: 1925 GN Cognac Special
By: jon.pearce Date: December 20, 2024, 11:15 am
---------------------------------------------------------
1925 GN Cognac Special.
#Post#: 12173--------------------------------------------------
Re: 1925 GN Cognac Special
By: Jimr1999 Date: December 21, 2024, 2:35 am
---------------------------------------------------------
Looking forward to reading it here Jon, as so much good stuff
disappears on Facebook. We spend a lot of time referring people
to good practice with links to build journal pages and this
helps everyone building. Seeing the journey end to end warts and
all, failures and successes, informs our members and helps them
develop their own ideas or avoid mistakes. We tend to be a
positive audience compared to some of the snipers on Facebook
too. Thanks for doing this. It really helps the club grow in a
positive way.
JimR
#Post#: 12178--------------------------------------------------
Re: 1925 GN Cognac Special
By: RhysN Date: December 21, 2024, 11:25 am
---------------------------------------------------------
I love the full size one, your little one will be equally great
I am sure. Perfect inspiration car IMHO
#Post#: 12181--------------------------------------------------
Re: 1925 GN Cognac Special
By: jon.pearce Date: December 21, 2024, 1:03 pm
---------------------------------------------------------
The beginning....
After first seeing the Cyclekarts at Middlezoy and chatting to
the folk there, I decided to start a design straight away !
My background is engineering and I have a karting restoration
business based in Wiltshire. (Handy)
I came away from Middlezoy with some firm decisions and build
requirements:
I have always LOVED the 1925 GN Cognac Special car, so this was
a no brainer for my inspiration car!
My build requirements and preferences were:
Something as low as possible, VERY LOW CG, Wide, adjustable
Track, Lightweight (under 100kg), but robust.
Wheelbase about 1750mm.
Parallel chassis rails, as per the original car.
I have a couple of used Subaru KX21 kart Clone engines that are
9.5hp, so plan to use them initially.
A Live 25mm axle, mounted above the chassis rails.
Hydraulic, KC30 2 pot Kart brake, etc, with a 200mm x 6mm disc.
(I had in my spares)
Hydraulic, Line Lock Handbrake with Venhill Powerhose brake
lines.
The option of adjustable track, front and back, up to the max of
1000mm.
I wanted CDS2 round tube chassis rails in 35mm od. (as I had
enough left over from a kart build)
I had a Jecko kart seat spare that I wanted to use and the width
of the seat dictated the overall width inside the chassis rails.
I decided on 17 inch, steel pit bike wheels with Cougar 2.75
tyres all round. I got these from "Funbikes" and delivery was
super quick.
I wanted to have an aluminium body and floor tray, etc, that was
bonded to the superstructure, to avoid too many rivits and
Nutserts.
To keep the CG low, a floor mounted aluminium fuel tank (2.5
litres) was made and submitted to CKUK for approval !!
Shortly after the Middlezoy event, I got in touch with Mark
Underdown and he supplied me with some SUPER QUALITY parts, such
as my Front Leaf Springs, Steel Hubs, Long 1090mm Rear Axle,
Faux Brake Drums, Steering Wheel Blank, etc, etc.
Budget = £1000. (which is achievable if you do lots or work
yourself) lol
Once I had most of the parts, I drew a half size drawing on a
sheet of wallpaper and worked out all the angles and potential
clashes !
It was then time to start building it ......
#Post#: 12185--------------------------------------------------
Re: 1925 GN Cognac Special
By: jon.pearce Date: December 22, 2024, 10:17 am
---------------------------------------------------------
Building Sub-Assemblies...the way I go about building things !
lol
I am a great believer in building as many "off the job" sub
assemblies as possible, before starting on the actual chassis
build !
First, I made the entire Front Axle assembly with 1/4 elliptic
Leaf Springs, stub axles and front wheels.
Second, I made the entire Rear Axle, ready to fit to the Bearing
hangers once the chassis was made.
GN Front Axle:
Main Tube is 32mm od CDS2 Drawn Tube.
Spring Hangers are 4mm laser cut items from Mark Underdown.
Lower Radius Rods are From McGill Motorsport with M10 Rod Ends.
Steering Yokes are from Mark also, and have 4 x Steering Arms
per item....you just cut off the arms that you dont need.
Stub Axles are standard OKE items with 17mm spindles.
I made Jigs as shown, to keep everything in place during tack
welding.
All welding on the axle is TIG welded.
Kingpin Inclination for my build was 15 degrees.
Zero Camber.
Ackerman angle for the steering arms was perfect for 1750mm
wheelbase and meets perfectly in the centre of the Rear Axle.
AN INTERESTING THING TO NOTE:
Leaf springs very seldom have an even amount of bend in them,
about the centre line !
I bought 1 x Spring and cut it in half to make 2 x quarter
elliptic springs. (Keeping costs low) lol
When fitting the springs, the axle didnt initially sit
horizontal and I had to pack one of the springs with a 3mm thick
packer.
Mark is long aware of this and smiled when I reported my
realisation !!! lol
Rear Axle:
The original car has a "locked Diff" arrangement, so I wanted to
used a "Live" rear axle.
Rear Axle is 25mm od and 1090mm long. Mark made the axle to my
drawing with M8 tapped holes at each end and long 6mm keyways
just where I wanted them.
Rear Sprocket is 98 tooth, 219 pitch kart item.
Rear Disc is 200mm diameter and 6mm thick.
To avoid using heavy steel, split clamp collars, I chose to make
thick wall, Aluminium Tubes to fill the axle space between the
inner face of the rear hub and the axle bearing.
This coupled with a large, 6mm thick washer on the ends of the
axle, locates the axle and basically it cannot move, which I
believe, is most likely the reason for de-railed chains and
binding disc brakes.
Rear Hubs are from Mark, very much like the Renegade items and
super quality.
Friction Dampers:
I had to make my own Friction Dampers, as the ones from Mark
were a bit too short for use on my chassis.
Actually, the Friction Damper placement on a GN car is very
difficult to get right, so much experimentation was the order of
the day.
I had them laser cut from 2mm Stainless Steel.
Now fitted, they look very period and work remarkably well. I
managed to locate a super, zero stiction material that makes the
dampers work properly.
#Post#: 12186--------------------------------------------------
Re: 1925 GN Cognac Special
By: jon.pearce Date: December 23, 2024, 11:01 am
---------------------------------------------------------
GN Cognac Special....Chassis & Frame.
Main Chassis Rails are 35mm od CDS2 Drawn steel tube.
Front "Swan neck" is 25 x 50mm x 2 RHS.
Cross Members : 16mm, 20mm, 25mm, 30mm x 1.6 ERW.
Bulkhead Hoops are done by a local fabrication company with a
Hydraulic, 3 Wheel Roller. They are 20mm x 2 ERW.
Steering Column : 20mm CDS2 Drawn Tube.
Engine Mount Plate : Slimline Plate to my design. Laser cut and
Folded, 4mm S275 Mild Steel.
#Post#: 12188--------------------------------------------------
Re: 1925 GN Cognac Special
By: Jimr1999 Date: December 23, 2024, 12:44 pm
---------------------------------------------------------
Looks fast already Jon! :) Whats with the Jubilee clips near
the hub?
JimR
#Post#: 12189--------------------------------------------------
Re: 1925 GN Cognac Special
By: jon.pearce Date: December 23, 2024, 12:46 pm
---------------------------------------------------------
The Iconic GN Radiator and Stone Guard.
Cognac has a Fabulous shaped Radiator Top and Surround.
....this caused me a bit of design head scratching before I had
the "eureka" moment.
I didnt want to have any fibreglass parts on the kart, so looked
elsewhere....! lol
I had some offcuts of very good quality Baltic Plywood in 18mm
which I made the profile from.
The double curvature top part was eventually produced by cutting
a turned, wooden fruit bowl in half and glueing it to the
Radiator back plate.
A bit of filler and a few coats of paint and it came out very
well !
The Stone Guard was made from Stainless Steel diamond mesh and
made a complex part very easy to build.
Large openings in the ply backplate save weight and make it easy
to pass the steering column through.
#Post#: 12190--------------------------------------------------
Re: 1925 GN Cognac Special
By: jon.pearce Date: December 23, 2024, 12:54 pm
---------------------------------------------------------
Thanks Jim,
The jubilee clips are simply to pinch the tubular alloy spacers
and stop them rattling on the axle ! lol
*****************************************************
DIR Next Page