Pit Bike Frame Build

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Blackdavid

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Hello, im new to the forum, just registered minutes ago.
I ride motocross(Honda cr250), but a 250cc 2stroke drinks a LOT of gas, and gas is expensive in my country, so i want to build a small bike only for fun, and for my mechanics class. I am looking for plans to build, pictures of frames, measurements of frames, everything that can help me!!
Thanks :)
 
I am a mechanic, so i know how to build things, and i have all the instruments.
I am looking for a good project, not one crappy and easy to build..
 
welcome to the forums,

check out my Orion thread, that may give you some ideas.
the link to the thread is in my signature.
 
Pit bikes in my country are not nearly cheap, you cant get even a chinese bike for under 500$!
I dont want to mod a frame, i want to build it from scratch! And looking for plans or measurements or anything..
 
sorry there is nothing here like that, well not that i've seen...
what country are you in?
spend some time looking at motorcycle wreckers, old frames etc etc, and get a heap of ideas
then start making some plans.

maybe look at some of these sites?
http://www.knucklebusterinc.com/features/2008/09/19/tube-welding-motorcycle-frame-building-basics/
http://books.google.com.au/books?id...A#v=onepage&q=making motocross frames&f=false
http://www.physicsforums.com/showthread.php?t=16510
http://www.wisegeek.com/what-are-the-different-types-of-mini-bike-frame.htm
 
Easiest way is to jig off another frame ...

Good luck making one from scratch , it will be nothing but a pain in the ass trying to find components to fit if you don't at least make most of it a copy off a generic bike like a crf50 ..

And i reckon it would be a long shot finding minibike frame with all the exact measurements written up somewhere ..
 
+1 to what woggy said.. jig it off another frame.. china dont deal in exact measurements with these bikes...

also iam 6'2" and i ride a 50 style frame and have no drama's.. although i wouldnt mind timmeh to get me a set of of similar bar risers... the pro tapers make for better clearance for sure...
 
Would you fit ? your making the frame so make it a inch or two longer lol ?

In front of the front tank mount you can lengthen a inch or two without throwing any other measurements off.
Also put on a longer swingarm ..

But if you can jig off a crf70 or klx110 frame that would be a better option for the bigger person ..
 
Yes i will build it, but I need a good soul to measure the frame for me, because i have no pit bike. And when i getvthe measurements i will tell if i fit or no and then longer the frame, i just need measurements! I googled everything possible but nothing!
 
Again i wouldn't even attempt it unless you got a frame to jig off right infront of you in the flesh .. getting every single measurement for every bolt hole /mount etc on any type of minibike frame is gonna be near impossible...
 
complete scratch built frames?

tricky stuff but not if you do them regularly.

measurements seem to be the factor here...where to start?

what engine? iunno what country youre in but everyone should have hondas! z50, sl50, c50...or 70's. copy those engine mounts, as theyre china motor standard sizes, and surely, anywhere, china parts are cheaper?. not sure about the larger honda 90/110's such as the "nice", as found in other countries. not in au... all i know is the CT (aussie=postie) 90 and 110's are not the same engine mount pattern!

ground clearance? wheelbase? what forks? you can fabricate up a set of springer/linkage forks if you have someway of making decent pivots...brass bushed preferably.

suspension travel. dependant on shock.

swingarm length? a component of both wheelbase and ground clearance, and the shocky mount position is determined by possible wheel travel, as well as the shock.
the ratio of length for the swingarm pivot to shock and swingarm pivot to axle is the leverage applied to the shock, which is where spring pressure/rate is important.
heavier springs allow for longer swingarms/ more leverage, but require more engineering to take the extra pressure... you can also get more travel from a given length shockie.

angle of shock during travel affects "rising rate"... the correct angle and its progressive, the wrong angle and all the flaws of the shockie itself (internal design) become more apparent, or the thing just wont work. the two extremes.


headset/ steering angle/ fork rake/wheelbase/trail....

commercially, most headstem tubes are welded then machined to take the bearing cups/seats. a really hard thing to do at home... got a mill? and adjustable boring head? otherwise accuracy is reduced...could be safety issues.

the angle of the tube affects turning speed and stability. it affects wheelbase when combined with fork length. theres rake; offset of axle parallel to head tube, and trail; how far the axle is behind the tyres contact patch in a vertical line. both affect stability and steering.

and everything has to be centralised in the direction of travel... chain offset... brakes...exhausts...pedals/controls... best to leave it to the pros... start saving... if you can get a cr250... bikes must be available...

i got some old yamaha600 thing here thats just wanting a 140 or summink stuffed into it....


nah. this is really the wrong forum to be looking up info on scratch built frames...

just bought ones :)

the list of measurements is pretty extensive. and possibly beyond the scope of anyone not familiar with marking out tables and real measuring equipment like calipers.


the other option is to measure pictures and scale them ;) then its jig time
 
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+1 to the above. It seems quite easy when you look at 90% of the frame in the middle, just weld some tubes together and a few lugs to accept bolts right? yep you could certainly do that. Ignoring the fact its going to look bodgy and would be rock hard and transfer every little bump straight to your bones, you could actually do that

But then you got to look at the hopelessly complicated bits on either end, and at the top center where the rear suspension delivers all the impact. That center piece has to be pretty strong, again doable. But the steering head and swingarm? yeah good luck with that. Those 2 pieces are a significant portion of R&D for bikes, very slight angle or length adjustments throw the whole feel of the bike in a different direction
But lets ignore that, lets assume you just want something rock hard that handles like poo
How are you going to get the steering head and suspension linkages smooth, accurate and straight? They need bearings in them with very fine tolerance, gotta be pretty damn smooth to get them in there. And they then need to welded on pretty damn straight

I mean kudo's for thinking of doing it. But lets be realistic here, the cost involved of using the precision machinery to get it all done right is going to exceed the cost of simply buying a frame. I can't imagine much 'street cred' when its going to turn out looking rather plain and bodgy. And it'll ride and handle like rubbish unless you copy some tested and proven specs on proper bikes

The whole project screams of '****ing around' to me
 
Look guys, all the machinery is free for me as i have 1 big mill, 4 lathes, a plain and some 3 tons parallel shers that can cut to 5mm metal, so it kinda wont take much. I have pipes at home of 5 meters, 4cm diameter, and even have a pipe bender! i am not ''new'' in building, neither in motorbikes, or motorsport anyways. I have TIG,MIG, oxy/acetilene welder, and electric welder, i have almost everything to build a simple frame FOR FREE!
I can make the head steering tube on a lathe, thats an easy job, i can take bearings from another bike.
Swingarm mount? At school we have a malaguti grizzly 50cc pit bike, i can take the suspension attach angle from that bike, and just copy it. Im good at welding, i will pass 2 times every weld anyways, and i like to make things ''like god says'' so it wont look goofy, i will sand everything down,every sharp edge will be smoothened and i will zinc spray the frame and then paint it.
The forks? I will buy some used forks for cheap, there are some used in my country, this thread is about building a FRAME not the forks.
Swingarm? I can make a swingarm too, its not too hard and i already made the whole swingarm for my moped, and also welded my aluminium CR250 swingard and it still hold all the jumps.
If you have some measurements to give me, then please help, if you came here just to learn me a lesson, i know what am i doing, and i dont need someone to demolite my project, neither to offend me. Wanna help? You will be welcome. Wanna offend? The back arrow is in the left corner. thats it

P.S: I CANT take the malaguti grizzly as it doesn't belong to me, neither he sells it.
 
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go for it mate,
there are people on every forum that like to jump in and flame,
but im sure you would be used to burns from every angle anyway, just like me

it isnt as hard as the others have made it out to be.
if i can modify my frame to the extent i have, im sure you will make the frame easily enough.
the degrees and measurements dont need to be within a .0001 of an inch.....
even with alignment, there is a fair amount of area allowed for adjustments.

keep us posted on how you go
cheers, craig
 
Thank you! i will surely keep you updated, i asked some measurements on other forums, and already found some but not what i am looking for, if someone need easy plans with all the measurements i am glad to give them on PM.
 
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