CycleKarts GB

Forums => Build journals => Topic started by: Slack Alice on 23 May 2019, 09:06:15 pm

Title: New build start..GN Thunderbug.
Post by: Slack Alice on 23 May 2019, 09:06:15 pm
I spoke to Chris And a few others at Stretton, and said I fancy building the GN Thunderbug. Iíve got the garage empty now and the first job will be to construct a building table, about 600 high. Then I can layout chassis etc...
Iíve acquired some 17mm kart spindles, and I think they will fit the design well.
I fancy a rack and pinion ( see other thread!!)
Iíve also picked up some bike engine bits in order to build a realistic looking v twin.
It will add weight but it is necessary.
What approx. Diameter is the final drive sprocket on the rear axle.

Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 24 May 2019, 09:07:26 pm
The answer to your question on approx diameter of the sprocket depends on; what ratio are you intending to use and what variety of the 4 "normal" chain versions.
Title: Re: New build start..GN Thunderbug.
Post by: StefanN on 24 May 2019, 09:53:35 pm
72 teeth on 0.5 inch chain is approx 11.5 inches in diameter
(72*0.5/3.14)
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 25 May 2019, 09:03:52 am
Thanks. I think I am about to buy an engine and TAV unit so that I can see what space is needed. Has anyone gone recommendations on a suitable combination/supplier?
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 25 May 2019, 09:14:58 am
Gemini Karts Rushden, good products VERY fair  pricing, and they support the hobby.
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 26 May 2019, 05:26:54 pm
Well...itís a start!!
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 31 May 2019, 01:53:53 pm
Right guys..some 17Ē wheels arrived today. How do I get the bearings out to replace with 17mm ID bearings?
Title: Re: New build start..GN Thunderbug.
Post by: StefanN on 31 May 2019, 03:38:54 pm
I used a copper drift to knock mine out, working from the opposite side through the centre of the other bearing.  The tricky bit is catching the edge of the bearing with the crush tube in the way.  I then tapped the drift with a hammer moving around the edge of the bearing to keep is square to the seat.  Once the first side is out, the other side is much easier. Good luck
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 31 May 2019, 06:32:50 pm
Thanks Stephan. Yes, that inner tube gets in the way, thereís not much of an edge to get the drift on!
Title: Re: New build start..GN Thunderbug.
Post by: ChrisS on 31 May 2019, 08:27:18 pm
I ended up dismantling the bearing on one side by destroying the cage and then working all the balls round till they were all touching each other, then the centre can be broken free by a smart clout. This allowed me to remove the centre tube and drift out the opposite bearing but left the outer still in place on the first side and the only way I could get it out was by reassembling the balls and the centre and using a drift on the bearing centre.  Long winded I know!
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 01 June 2019, 06:54:13 am
TBH, I have never had too much trouble. As you are not going to re use the bearing who cares how much you damage it. I use a steel , sharp edged punch, first hit is to move the "crush tube across one way so you get a an edge on the inner of the bearing. Don't worry about getting to the outer race.
Once it has started moving, even a tiny bit, I just go from side to side giving the bearing a reasonably hard hit with a reasonable size hammer. Small hits with small hammer is more likely to cause damage.
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 01 June 2019, 06:23:36 pm
Thanks everybody...job done. Very sharp (tungsten) chisel did the trick. Just waiting for the new bearings now.
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 01 June 2019, 06:32:15 pm
Next issue...TAV modifications.   Engine and TAV have arrived and preliminary tinkering suggest a 10. o clock setting. This needs removal of some webs.
I know this has been done but are we OK with the process?
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 01 June 2019, 07:22:16 pm
Simple answer, yes.
I have used 6 o'clock for the last few.
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 01 June 2019, 08:30:22 pm
Ok Iíll check that out tomorrow. I see some karts use 4o clock. Iíd rather not remove the webs.
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 02 June 2019, 07:19:35 am
Unless you have the chain running directly back from about a 4 o'clock mounting you have to, at least, massage ribs. These units were originally made for mini bikes and designed that way.
Don't worry about taking off ribs, I have heard of nobody having issues as a result.
Title: Re: New build start..GN Thunderbug.
Post by: Adrian on 02 June 2019, 12:24:25 pm
I am in precisely the same qundry.
Is it OK to remove the stiffening ribs  on the crankcase?
Adrian
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 02 June 2019, 05:58:09 pm
I would not touch the crankcase, some castings are very thin. The TAV can handle it.
Sorry to hear about you being a new member of the "Some bast$%^ stole my welder club" Adrian.
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 05 June 2019, 10:10:19 pm
Inspiration!  Really fancy building it fun size!
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 11 June 2019, 08:00:40 pm
Been working on the front axle...nearly finished. Iíve put a rack on it ( bought before the recent discussions on the forum !)
Also working on a V twin engine. Itís got to look realistic, BSA bantam cyl. Heads, scooter barrels and plastic drainage pipe for the main barrel. Got some small carbs as well!
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 13 June 2019, 11:10:11 am
Chassis works continue....the stick welding is not producing a pretty picture!
Title: Re: New build start..GN Thunderbug.
Post by: Chris Brown on 13 June 2019, 12:21:07 pm
To follow on from your question on Stefan's post regarding your radiator cowling.

There are an number of ways to tackle it:

Find something the right basic shape and trim it to suit, sink, water tank plastic trough.

Find something you can use as a mould, baby bath or similar.

Sculpt it in foam as Stefan has, mould the body shape over that, fill, sand and paint the outside to get the finish you want.

I'm going to try using the chrome car wrap on the Morgan radiator surround.
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 13 June 2019, 01:51:07 pm
Thanks Chris...I kinda like the foam/glass mat/ filler route. I can sit and sand it whilst watching the telly !!
Title: Re: New build start..GN Thunderbug.
Post by: Chris Brown on 13 June 2019, 02:02:13 pm
If you go down that route then wait until it has gelled (just gone rubbery), and apply a glazing coat. You can buy glazing coat resin, or just make it up from 1 part laminating resin, 3 parts gelcoat, that'll make finishing a lot easier.
Title: Re: New build start..GN Thunderbug.
Post by: Steve Cole on 15 June 2019, 08:52:04 am
I would not suggest making up a ďGlazing coatĒ !
fibreglass your piece, let it set then screed it with an easy sand car bodyfiller.
Then sand it down when itís set. Anything gelcoat or resin with be much harder to sand down
This kind of stuff is what you want to use
Title: Re: New build start..GN Thunderbug.
Post by: Chris Brown on 15 June 2019, 09:20:52 pm
As I use it the glazing coat simply gives a smoother base for the filler, and reduces the amount of sanding needed, it's not a final coat. I should have made that clear in my comment, sanding goes down to the glazing coat not into it. I usually pigment the glazing coat black to give a teltale when you reach it, it also means you don't sand into the glass.
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 19 June 2019, 01:15:37 pm
My friend David, ďtechskillĒ on the forum, has taken on the grill for me! David was with me at Stretton last month.
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 19 June 2019, 02:36:09 pm
What grill(e) :) ?

BTWmy friendly sign guy has the artwork for the GN logo as on Thunderbug. Yell out if you want a pair of red ones. You need to figure the size.
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 22 June 2019, 07:56:48 am
Progress on the build. David has spent two days carving out the grill shell in wood! Itís far too good to cover up so will just paint it.
Engine block is made and will start assembling the rest of the engine today.
Have bought an old kart seat and have widened it to suit me!
Starting to cut up plywood and think about getting in and out of the thing! Itís going to have to be sturdy around the seat area.
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 22 June 2019, 08:21:09 am
That's looking really good. Love the rad shell, and you are right, matt silver paint. It's a bit too nice for Thunderbug, looks more like a show piece :)
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 25 June 2019, 09:40:53 pm
Engine mounted but not yet started up! Maybe tomorrow.
Drive connected with #35 chain and split link. Disc on, with Ďsmallí cable operated calliper....probably too small, but had it lying around! I think I need to control lateral movement of the axle. I am going to put locking collars on but feel inclined to add a steel plate to the chassis inside, to act as a thrust bearing. Any thoughts?
I would just grease between the plate and collar.
Body work started with the floor. Iím using 9mm ply. There is enough for the sides as well. Bonnet in alloy, and rear bodywork in alloy.
Most people have a removable rear section. More work...!
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 26 June 2019, 06:57:51 pm
Lock that axle with lock collars. The split ones work best. If you don't you will get brake bind and probably throw chains. (Learned the hard way)
With your caliper, just check to make sure it can move if it needs to, or doesn't if it shouldn't. i have something here where the caliper had been bolted up, so to get the other side from the moving piston to work the disc itself was bending.
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 27 June 2019, 09:53:46 pm
Thanks Rhys...already ordered some locking collets. Calliper body slides when applied so disc is not compromised.
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 28 June 2019, 10:40:01 pm
Steering coupled up today. There is a lot of play in the central part of the rack. Itís a plastic shell and doesnít seem to hold the wheel part particularly securely. Time will tell if it stays together.
Some more bodywork done, including the scuttle, Iíve put a steel frame behind it to support the steering column. The column is one piece with a Uj at the rack end and a sliding joint at the top. The whole column will move up and down as the axle moves.   Still lots to do!
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 28 June 2019, 10:43:26 pm
Forgot to add latest pics....
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 30 June 2019, 10:12:31 pm
Finally up onto its wheels! Spent the day connecting brake and throttle cables to the pedal setup. Will try and track down a 5/16 UNF bolt tomorrow for the crankshaft.
Should be ready then for a road trial! Just remembered...got to fix the seat in!
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 06 July 2019, 01:49:14 pm
HELP......first test drive this afternoon. Problem with TAV. The large pulley with the red spring is not tight enough, causing the outer part to jump past the rubber cones.
Is there a specific torque for this nut?
Title: Re: New build start..GN Thunderbug.
Post by: StefanN on 06 July 2019, 02:35:54 pm
I donít have the info with me but I got it from a manual I found online.
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 06 July 2019, 04:13:47 pm
Have you had it apart? I know that I did once and assembled it with the driven plate the wrong side of the rubber cones. I'm not sure that red spring is the right one, obviously could be wrong, I thought it was the green one. Colours mean different "strengths". Try giving Gemini a call.
 I seem to remember 45ft lbs.
Try this youtube link, all is revealed. https://www.youtube.com/watch?v=kmGY0qsgW4Y
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 06 July 2019, 07:10:15 pm
Panic over guys....turned out to be a loose chain. My neighbour said it was the cone...I thought it was the chain and I was right! 
Drives like a pile of ****.  No brakes.....needs work!
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 07 July 2019, 07:42:10 pm
The car looked great, and for maiden voyage went really well I think.
The front engine is a work of art, really great.
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 09 July 2019, 07:55:45 am
After the drive, and again apologies, the biggest thing which I think might make it more enjoyable for you would be to lower the seat some. Otherwise I think it went pretty well. Brakes of course.
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 09 July 2019, 01:16:15 pm
Hi Rhys...thanks for your comments. I have got some changes to make! The brakes failed because the cable slipped at the joint on the pedal. I think I will go hydraulic now.
I was driving the CK like a kart, expecting too much in the way of handling. The high C of g doesnít help, poor brakes, and probably the two wheels driven aspect all contribute to a more gentle approach being required!
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 11 August 2019, 08:49:46 pm
Desperately trying to get the kart sorted for Stretton.
New hydraulic brakes fitted, as yet untested!
Aluminium acid primed ready for paint and Iím busy creating a mock petrol tank to sit above the engine.
Iíve re jigged the throttle on the engine. I saw a utube video of some guy Ďbypassing the governorí. Thought Iíd give it a go.
Unfortunately, whilst turning what I thought was the throttle stop, I seem to have upset the mixture! Does anyone know the original setting?
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 11 August 2019, 09:57:04 pm
On most original type carbs the only adjustments you can make are the idle and full throttle stops. If you can take a photo help may be available!
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 12 August 2019, 12:43:13 pm
Youíre right Rhys...the screw I was adjusting was the idle screw!  Didnít work before but does now. I thought the revs were too high...they were 2300. Should be 1700 ish. Have now adjusted it ok.
I have a rev counter if anyone wants to use it?
Also have a track measuring device. Been lying around for 50 years or so (!!) dead easy to check toe in. Iíll bring it with me.
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 12 August 2019, 03:47:10 pm
That's good news that it was solved so easily.
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 13 August 2019, 06:20:53 pm
Been painting today....had to show you these!  Definitely sunglasses needed !
Title: Re: New build start..GN Thunderbug.
Post by: TheGiantTribble on 13 August 2019, 06:43:01 pm
Looking very smart.
Title: Re: New build start..GN Thunderbug.
Post by: Slack Alice on 13 August 2019, 06:53:09 pm
Thanks Bill....did you sort out your TAV issues?
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 13 August 2019, 07:02:48 pm
Now you just have to apply "patina" to be anything like the original :)
Title: Re: New build start..GN Thunderbug.
Post by: TheGiantTribble on 13 August 2019, 09:05:24 pm
Yes, I think, well probably, maybe...!!!
Yup all fixed just got to bleed the breaks a bit more ready for Stretton, and fit the new exhaust.
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 02 October 2019, 07:40:46 pm
Just for you Dave.
Title: Re: New build start..GN Thunderbug.
Post by: RhysN on 02 October 2019, 07:42:17 pm
And another