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Spaz
3rd August 2005, 22:11
Well I've had a little bad luck with my GN so I was looking at giving her a new lease of life.
After watching Monster Garage evil plans started sprouting in my head and I went in search of information on home building choppers out of every day house hold items. Thanks to the wonder that is google I found this: http://www.vabiker.net/ads/chopper-frame.html oh joy!
More research informed me that I would need to construct a jig in order to construct the frame strait and true. I think all up the information will cost me about US$100 and then I would need to get materials, stuff up a few times, get more materials and then viola!
I'd also need to take a crash course in welding, find a mandrel, a new tank and someone to paint it.
Before embarking on that, is there anyone here who can tell me how to do it right and save me fluffing about in the 'encyclopaedia of American style'?

ALL input welcome (no matter what it is),
Cheers.

Ixion
3rd August 2005, 22:20
Planning to ride it on the road? If so it will need low volume certification, and you'll need more than a crash course in welding to produce a frame from Reynolds tubing. Unless you use heavy gauge tubing and braze it the old way. Easier to do, but it would be heavy, and you will not be able to get the gusset forgings.

A very ambitious project for a GN250. Not wishing to rain on anyones parade, but maybe best to check things out fully before making any commitments.

What was the bad luck with the GN ?

Hitcher
3rd August 2005, 22:30
Are you serious about chopperising a GN250?

Spaz
3rd August 2005, 22:31
Guy ran into the back end of me while I was sitting at the lights, it's rideable but there is something wrong in the frame.
I thought with all the hype that is going around this style I would be able to get something out of it if I did it well (skill and $). GN's are really slack when it comes to power so I would need to do it with weight in mind.
Cheers

Spaz
3rd August 2005, 22:34
Are you serious about chopperising a GN250?

I need a project.
Much like the apple was to Newton, a Toyota Corona is to me.

Waylander
3rd August 2005, 22:44
What exactly is wrong with the GN frame? It' would be easier for you to use that frame and just change it a bit. Stretch the top tube and down tube, widen the rear swingarm and such like that. Would make it much easier on you down the line when it came to registering if the frame already has VIN# and such.

Looking at doing one myself out of my CMX once everyone in my family and a few friends use it to get thier lisences on.

Spaz
3rd August 2005, 22:52
What exactly is wrong with the GN frame? It' would be easier for you to use that frame and just change it a bit. Stretch the top tube and down tube, widen the rear swingarm and such like that. Would make it much easier on you down the line when it came to registering if the frame already has VIN# and such.

Hmm, I'm really not sure what's wrong with it, whatever it is it's not shocking news. I thought getting rid of it and making a new frame would fix the problem but that sounds bloody good to and it would get me around the VINing problems. I might find out what the problem is when the bike is compleatly apart
Cheers

Waylander
3rd August 2005, 23:04
Hmm, I'm really not sure what's wrong with it, whatever it is it's not shocking news. I thought getting rid of it and making a new frame would fix the problem but that sounds bloody good to and it would get me around the VINing problems. I might find out what the problem is when the bike is compleatly apart
Cheers
Yea find out when it's appart. If it is just the swing arm then sweet. Exspecially if you want to put a bigger tire on the back. You would have to replace or heavily modify it anyway.

Keep in mind though that GN motor wont be able to turn anything too fat so I wouldn't go anything above maybe a 170 or 180.

Odin
4th August 2005, 07:33
It sounds great and all the luck in the world to you. sometimes its great just jumping ind and then finding out if one really CAN swim or ...
Just be sure to think it trough first, if you build a new frame you will most likely also need to get a new wirering harness and things like that.
As to painting you should be able to do that your self. That would be one of the easier parts of the project i'd say. Unless you want a real custom job with flames and the like.

But keep us opdated please :drinkup:

FzerozeroT
4th August 2005, 09:15
for the price of the plans and to build your own jig you could probably pay someone to build it for you

White trash
4th August 2005, 09:32
Hey Spaz, cool idea man. But don't junk the original GN frame. The bit that;s buggered sounds like the sub frame if you were hit from behind. That's easy enough fixed or replaced.

Keep the main frame as it already lines up your steering head and swingarm mounts nice and straight. If you strip the frame right back, a decent engineer will be able to "strecth" and "rake" front end and build a diffeerent subframe to suit your new "Low rider".

Wouldn't be my personal choice of chop' but each to their own, go hard.

Odin
4th August 2005, 09:46
for the price of the plans and to build your own jig you could probably pay someone to build it for you

And how much fun would that be ?

I say go for it, if nothing else it'll give you something to do and develop some skills and hopefully show some caracter when its all finished :Punk:

ezinnz
4th August 2005, 19:56
If you go ahead and modify the frame it will need inspection for certification as previously mentioned. If you take it to an engineer to do the job, make sure he has his welding ticket because you'll need to prove he is a certified welder to do structural work on your frame. If you can't produce this, the certifier will most likely ask you to have the welds x-rayed for cracks. This is specialised and expensive.

You could stick to your plan and learn to weld and have some fun. That's what it's all about. Maybe not ever get it certified for road use. I'm a fairly experienced welder but I still wasn't keen to try and build my own frame. I had a guy with a lot of experience build an 'open space' frame for me and then I put all the engine mounts, tabs, brackets etc on it to suit.

A failing frame at any speed will hurt. You can't be too careful with this part of your build.

Hope this helps.

Storm
4th August 2005, 20:16
Have a go mate, that's what makes Kiwi ingenuity so good. Be sure to keep pics and updates flowing

phantom
5th August 2005, 09:45
I'm still waiting to see were the string instruments come into it

Waylander
5th August 2005, 12:06
On painting your tank, I'll be painting one myself once I strip it of the current paint and make a few other mods to the tank. I've got a compressor and a paint gun if you need those to use. They run on 110 rather than 220 so it has to go through a transformer but I got that covered. It'll be a while before I paint my tank but if you want to bring yours down on that day we can do them both at the same time.

Spaz
5th August 2005, 21:48
It would be easier for you to use that frame and just change it a bit. Stretch the top tube and down tube, widen the rear swingarm and such like that.

This plan sounds something like what I think I'll do. what kind of tools and information will I need to find?
I am no engeneer so I have no idea how exactly I would stretch any tubing and keep it strait.

Cheers

White trash
6th August 2005, 08:35
This plan sounds something like what I think I'll do. what kind of tools and information will I need to find?
I am no engeneer so I have no idea how exactly I would stretch any tubing and keep it strait.

Cheers

You don't "stretch" it as such, more like cutting it and welding a longer bit in here and there.

This is also going to effect the handling of the bike severly, and not for the better by any stretch of the imagination. You wanna read a book or three on chasis design to understand all the bits like "rake" and "Trail", and more importantly, the effects each change will make to your machine.

Waylander
6th August 2005, 12:59
You don't "stretch" it as such, more like cutting it and welding a longer bit in here and there.

This is also going to effect the handling of the bike severly, and not for the better by any stretch of the imagination. You wanna read a book or three on chasis design to understand all the bits like "rake" and "Trail", and more importantly, the effects each change will make to your machine.
This part he got right.

Yea do lots of reading up on this before you actually try it. There are a few books out there, (don't know if they are here cause I havn't seen them yet but I havn't really looked either) that will help you understand the basics of what you'll be doing before you get to the heavy stuff. These two here (http://www.speednation.com/store/product1423.html) and here (http://www.vabiker.net/html/books-1929133170.html) are good ones to start with.

They help explain some of the terms and a few of the technical bits so that you can understand the more advanced ones.

TLDV8
6th August 2005, 14:29
Anything is possible,but a basic knowledge of engineering/welding would not be enough to cut a frame (imho)...

It is easier to take it out than put it in..in days gone by it was not unusual to simply cut and remove a section of the top tube,then heat and bend the lower tubes to increase the rake,then reweld the top tube..

Here is a Ducati frame, rake was decreased by around 7 degree's by removing the stock steering head tube,recutting the frame tubes at the desired angle on a frame jig,then machining a new tube and welding it in :whistle:

<img src="http://img.photobucket.com/albums/v63/manurewa/stock.jpg" alt="Image hosted by Photobucket.com"> <img src="http://img.photobucket.com/albums/v63/manurewa/modified.jpg" alt="Image hosted by Photobucket.com">

hondacmx450
12th August 2005, 19:23
if you want the number of a person in auckland to talk to pm me i have a mate of mine that has just done what you want to do but he did it to my old drag bike now it is a drag choper and nice to

Waylander
15th August 2005, 01:14
Some late night reading...

These are mostly for if you want to build a new frame from fresh materials but you might find a tid-bit or two that could help you out.


http://64.172.168.34/neatstuff/

http://64.172.168.34/neatstuff/old_school_chopper_frame.htm

http://garagechoppers.com/archives-Chopperfreak.shtml

http://garagechoppers.com/archives/000675.shtml

http://garagechoppers.com/archives/000698.shtml

Waylander
15th August 2005, 01:32
Just found something that might help you more. Explains how to do the welding of new pipe into the exhisting frame to "stretch" it out and a few other things.

http://garagechoppers.com/archives/000502.shtml

And the whole "rake" and "trail" thing.
http://garagechoppers.com/archives/000476.shtml

clint640
16th August 2005, 11:53
If you are going to build or modify a frame:

TALK TO THE CERTIFIER FIRST!

There will be someone around that cert's bikes, talk to them before you do anything, tell them what your plan is in detail, ask them exactly what they want to see when you turn up with the finished bike. Write it down.
The cert guys I've had dealings with when modding my 4x4 have been good blokes who are happy to take the time to help out. If you keep them in the loop from the start the inspection will be a mere formality.

If you are 'no engineer' you might want to ask yourself is it worth putting over $2k (cos that's wot it'll cost, the cert alone is $400) into a GN250, but I like a crazy plan so good luck.

Cheers
Clint

RedRocks
5th October 2005, 10:27
Mate don't try this at home! Chances are you'll chop ya fingers off or have a few ACC moments along the way. Also your welding needs to certified, then the bike needs to meet LTSA requirements & get certified too. What a nightmare!!!

If your serious about building a bike, let me know. I can build you a tank and fenders using mallets, sandbags and an english wheel in about 5-7 days, all handbuilt, one of a kind....