homebrew chopper on the cheap

R

ridingpistonbroke

New Member
bmx frame rear end, and a huffy welded together pretty
much sums it up. i got a old haro i had lying around and
chopped the seat post off the the back part the wheel attaches
to,and had it welded on upside down.so the v,brakes are pointing
at the floor,and the seat post is angled back. i was going to have
stupid long forks,bt was talked out of it. this is only a first build.
the frame tubes connecting the huffy to the haro are old exhaust tubing.
already had the bends in the right places and is quite strong.
the handle bars are the stock haro bars chopped with a straight
mountain bike bar cut in half and sleeved on each side. i will
get straps welded to the un sleeved ends.

i need to move the top bar about 10mm up to make room for the motor.
the length might need some extending too,not sure yet.
we welded it up just off the top of my head,as we went.not the best thing to
do if your paying someone by the hour to help you. any way we got it together so i
could see what needed to be done.to be honest im surprised at what we made,
even though its far from done.a crank will have to put higher in the frame to make
it more comfortable to pedal,but the chain wont clear a motor hanging out. the motor
i am using will be a huasheng 49cc i bought last week,should be here this week or next.
until then i dont think anymore welding will be done.

the pedals will just be there to keep the cops off my back,and i plan on using a shift kit,
so i might just leave the pedals where they are and just use shorter crank arms to get it
up off the ground some,i don't really plan on pedaling this one. i have my mountain bike 2 stroke
for work, this will be for summer weekends for fun. i plan on having a loud exhaust
on this :). if i keep the pedals where they are, i can mount pegs up front of the motor
for my feet.believe it or not we tacked the seat on and rode it,just for a laugh with
flat tyres.your knees are high but its doable,kind of. the seat wont be quite that low, and
i shouldn't have to pedal really anyway. i need to organize some sort of sissy bar for it
too, my mate donated the seat from an old dragster.

so, i cant really do too much till the motor arrives,but im pretty amped about this.
in the end i hope to have it matt black,with hopefully a slightly fatter rear tyre,
skinnier front tyre and if im really lucky a disc brake on the front. im going to take my
time with this one and get it semi right.its not a proper chopper,but im sure i will be smiling
riding it down the street.thats what its all about imho.
if anyone has any comments or input they are appreciated.
cheers.
i dont have access to the bike that much but heres some pics i took.
donnybrookechopper003.jpg

donnybrookechopper004.jpg

should be good auflg
 
thanks for the reply's,i havnt been able to do any more
work on it yet as the motor isnt here,hopefully this week.
im thinking about raising the top bar an inch and lengthening
the bike two inches. also thinking about a homemade shift kit,cant
justify spending $230 plus shipping for one. may have to buy
the free hub thingo for the pedals,that seems a bit complicated,
oh and maybe a freewheel sprocket same pitch as the drive on the
motor. same amount of teeth aswel,probably an 11t. i could use an old
gear cassette on the other side if a i had too.

i lost my license and was into cars, this forum and my motorized pushy
has got me into bikes. hence this build,but i mean motorcycles too.
when i get my license back i want to get a 250 license and get a v twin
250 motor and customize a frame for it. where all this came from i dont know.
love it. stay tuned.
cheers.
 
ridingpistonbroke said:
may have to buy
the free hub thingo for the pedals,that seems a bit complicated,
Click to expand...

They are actually very simple and easy to make, freewheel cranks have been used in trials bicycles for years, all they are is a crank with a thread that a 'standard' freewheel screws onto, to that freewheel two sprockets are bolted, one is powered by the engine the other has chain to rear wheel sprocket. To make your own freewheel crank, you can use a standard 'european' style bottom bracket cup, they are the same thread/pitch as freewheels. Then you need a steel crank, simply weld the bottom bracket cup to the inside of the crank arm and screw your freewheel on, you can even use a one piece crank if you cant obtain a 3 piece crankset...They are cheap to buy from Sickbikes under 20 bux for freewheel crank IIRC but even cheaper to make if you have a welder...best of luck with the rest of the build...

KiM
 
thanks for the reply kim. something to think about.
to be honest im thinking of chopping the pedals off all together.
dont know if its a stupid idea or not but im definitely making a shift
kit (i was told not to bother but i am insistent on having it)

i got the motor about 3 days ago but havnt had the time to do much until
today. we raised the top bar top fit the motor,braced most of the frame
and tacked the engine mount in. the frame doesnt flow as good but when the
seat and sissy bar are fitted it should be sweet. i was advised to shorten the handle
bars some, which is a good idea looks quite good. i plan on having the pegs
just infront of the motor,to the bottom. so my legs sort of hug the motor,
my radical idea at the start has been altered for some drivability. its going
to be a pig as it is now, im glad i shortened the handle bars and didnt lengthen the frame any.
if anyone has any experience as far as "rake" goes, and the steering feel free
to chime in.

i havnt been able to pump up the tires yet to see how it rides,but i think she'll
be right. i have seen a stingray in the local paper for $400 bucks.:drool:
4 inch back tire. i know there are loads of them on the forum i often look
at them and just wish i had it.if i had the money i would buy that stingray,
and do that.

anyway heres some photo's. :)
not sure on the frames shape, but meh.
the motor-
donnybrookechopper019.jpg

modified frame-
donnybrookechopper024.jpg

donnybrookechopper022.jpg

donnybrookechopper023.jpg
 
ridingpistonbroke said:
if anyone has any experience as far as "rake" goes, and the steering feel free
to chime in.
Click to expand...

Do you know how o measure rake and trail? I can find a diagram if need be, what you need to try and aim for in between 2-4 inches of trail regardless of rake, any more and you will have very "slow heavy" steering that is very stable at speed but lower speed riding is more difficult, any less trail the steering will be twitchy/ over 'responsive' and can be 'nervous' at high speed, there is a happy medium between the two which by most accounts is between 2-4 inches of trail, where between this will depend on what the bike is and what you will use it for, downhill mtbs have less trail so they have nimble and fast acting steering while your average stretched out cruiser type bicycle has more trail for more relaxed stable riding. . I run ~2-3in on my cruiser and it is just right for my riding abilities and the bike is ultra stable at 45mph. If you don't get enough trail with a large rake you get what is called 'flop' this literally means when you release the handle bars they won't stay centered but flop to one side, this is not good for safety nor handling on road going bikes. Lemme know if you want a easy to follow diagram to workout rake and trail anywayz...i don't think i need to tell you how important this is to get right, it will make or break your bike...and/or your body if you get it hugely wrong :-)

best of luck buddy

KiM
 
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KiM said:
Do you know how o measure rake and trail? I can find a diagram if need be, what you need to try and aim for in between 2-4 inches of trail regardless of rake, any more and you will have very "slow heavy" steering that is very stable at speed but lower speed riding is more difficult, any less trail the steering will be twitchy/ over 'responsive' and can be 'nervous' at high speed, there is a happy medium between the two which by most accounts is between 2-4 inches of trail, where between this will depend on what the bike is and what you will use it for, downhill mtbs have less trail so they have nimble and fast acting steering while your average stretched out cruiser type bicycle has more trail for more relaxed stable riding. . I run ~2-3in on my cruiser and it is just right for my riding abilities and the bike is ultra stable at 45mph. If you don't get enough trail with a large rake you get what is called 'flop' this literally means when you release the handle bars they won't stay centered but flop to one side, this is not good for safety nor handling on road going bikes. Lemme know if you want a easy to follow diagram to workout rake and trail anywayz...i don't think i need to tell you how important this is to get right, it will make or break your bike...and/or your body if you get it hugely wrong :-)

best of luck buddy

KiM
Click to expand...

first off let me just say a huge thankyou KiM,for
taking the time to explain things. really does make a
big difference, especially seeing as im a bit of a dummy
and haven't done this before. i will look up trail and rake
as,to be completely honest i dont really know what they mean. lol.
once again cheers,its people like you that made me build this bike.
good on ya mate. hopefully i will have some more done this arvo.
might have a crack at some kind of sissy bar,good thing is my welder
has a "we can do anything" attitude and says i can have anything the
way i want it,which gives me confidence when everyone else reckons
it wont work. may also have a think of the jackshaft too. im a little
sad that its not a real chopper like the ones on the forum,but im a tight
ass and have to make do. :) more future mods might come as time goes.
im already thinking of a motorcycle wheel on the back,god knows how.
funny what you start thinking when theres a welder going. might just keep it
simple at the start and see how i go from there. love this hobby.

thanks for looking.
 
No worries at all, heres a couple of diagrams that will help you understand and measure the rake and trail.

Trail80rake.jpg


Most commonly dropouts on the lower fork leg are used to get the correct trail, but not always, forks can als be offset at the head to gain the correct trail required, can be seen in this below diagram.

raketrail.gif


The forks on your bike have an offset at the head rather than extended dropouts, alot BMX & MTB bike forks are like this., looking at the pics it looks like not quite enough for me but i could be wrong i often
am LoL..

Hope this clears things up, its not super difficult once you know what your looking at.

HAHA and yes, once you have a welder and an angle grinder the mind starts to create all sorts of things dont it haha ..best of luck, with lil practice you will soon be making bikes of your dreams...

KiM
 
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thanks again. i still dont quite understand it but at least
i can measure it when i see the bike next.

havn't done an awful lot,strengthening mainly. handlebars
got sleeved and welded top to bottom,straps welded underneath
crank and around the seatpost for the back half. bit overboard
really,its bombproof.other than that, the welds were cleaned up
and i started thinking about seating arrangements. (in case it wasnt mentioned
the seat post was extended about 2 inches up and the top bar bent,so the motor would fit)

i really wanted pegs out the front so i could stretch my legs out and lean
back,but that has proven impossible. feet would stop the front wheel
from turning,or you would be so far back you couldn't reach the handle bars.
my legs will have to be bent,and around the motor,and the seat maybe forward.
where it sits in these pics is o.k but when i turn the handlebars it stretches
my arm a bit. a sissy bar was made but its to heavy i think, i may not even
do a sissy bar i have other ideas.

for the jackshaft someone suggested not to even make one and weld sprockets
onto both sides of the hub when i cut the pedals off.two small gears. might be
a plan. i intend to have some kind of fake "clip on" system and keep some pedals
in my bag,try and keep the cops off my back. i can see me getting stopped the
first day.well yesterday i nearly threw the bike in the bin,and my welder mate i dont think
is overly impressed that i come down with no plans and just do what i think.
luckily im still on track. the bike doesnt quite look the way i wanted but i guess
its hard to tell atm. i put it down to being a first go and a learning process. if
i dont like it, i can unbolt the motor and start again.

if someone has done the hub/jackshaft idea or knows a bit about gearing,
some advice would be helpful. say the motor has a 11t gear, i was thinking put
another 11t on that side of the hub (same pitch obviously) and another 11t (bicycle chain pitch)
going to the bike chain/derailleur on the other side? i have to look at the motor to see of it will let
the chain will go downward,might not even work. or put a big gear on the motor
side for some reduction then a slightly bigger on the the other side,i dunno.
starting to sound like the jackshaft is easier to do. decision, decisions.

couple of pics, not the most exciting stuff.
donnybrookechopper026.jpg

donnybrookechopper025.jpg
 
ridingpistonbroke said:
if someone has done the hub/jackshaft idea or knows a bit about gearing,
some advice would be helpful.
Click to expand...
The way you outlined you wanted to do it ain't quite right buddy...

I have uploaded a gear ratio calculator for you to my ftp site you can download it and open it in Microsoft Excel and input sprocket size, rpm and wheel size and it will workout for you th exact size sprocket you need for your jackshaft and rear wheel sprocket in relation to the top speed you wanting to achieve it is what I used to workout the ratios for my builds.

KiM
 
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ok, just to make sure were on the same page i have done some
drawings on what im thinking,makes it easier for me to explain as well.
every idea i have here includes a rear gear cassette from a mountain bike.
how i do this i dont know,im thinking there are kids mountain bikes
whether they have a 20 inch rim im not sure but i could possibly swap
the wheel hubs and with a bit of modding get the cassette on the bmx rim.
im dead set on having the gears and a derailleur. that is the red thing around
the back wheel,needless to say my drawings are pretty ordinary.

standard jackshaft- 1:1,drives from motor to jackshaft,across the jackshaft and down
to the front gear where the pedals are. allowing use of the rear cassette gears.-
jackshafteone.jpg


my first idea- do the exact same but through the hub. use the front hub as the jackshaft.
using two gears the exact same like the jackshaft, would work but i think would ruin its bottom end climbing power. -

jackshafttwo.jpg


second idea- to fix this i was thinking swap the pedals large original sprocket over to the engine side,
and on the other side weld one on a bit smaller,like off a childs bike. this would definatly
climb hills, and i think may be the go.-

jackshaft3.jpg


i wouldn't know how to work out the gear calculator for this, especially seeing as i
might have 6 gears. i really need to find out how to get the gear cassette on the
rear wheel before i go any further.may just have to be a case of trial and error.
cheers.
 
This is exactly what the jackshaft calculator is for mate, it has provision for 6 speed cassette did you even look at it? It is pretty straight forward, put in the teeth number and it automatically gives you the answer whole idea of it.

KiM
 
not much progress,havnt really had the time. didnt look at the calculator,
for some reason my pc has every program but excel. handy. doesnt matter,
thankyou for posting it,i will use it later no doubt.

the seat is about an inch forward of the old pics and im going to use two
shocks i cut off the front of another bike to support it.these will have a bar going between
them and through the seat instead of a sissy bar with a pivot front. i should have a shock
absorbing seat in the end. i cut the crank hub housing thingo from another
bike and popped out the "circular cups/bearing race" things to make room for sealed bearings.
this will be my jackshaft in the end. just need to chase down some sealed bearings
to fit in there and get some sprockets. need to make a trip to the bearing
shop and this place i found out about today for some gears. the homebrew jackshaft
will be rather wide,there will be very little clearance for the chain on both
the engine and the pedals side.

i am going to get spring loaded pegs for it and other than the jackshaft, my other
concern is getting a gear cassette on the bmx rim and widening the frame to accept it.
tomorrow will be working in the rear wheel and hopefully some pics. i will be going with 11t
gears on the jackshaft and just going the traditional route. if i run into trouble, i do.
also somehow need to fit a mountain bike crank with at least two crank gears,
one for the jacksaft to come down onto,another for the bike chain.

sorry,no pics.
 
did some work yesterday and got the gear cassette on the
bmx rim, wasnt really that hard. found out aswel that rather than
modifying a crank housing to accept sealed bearings, a bike shop
should sell one with sealed bearings fitted,as one unit. that will
help,the only thing i dont like about bike shops are the prices.
100 bucks to re-spoke a wheel, i can get a new bike for that from
big w. so today i think i will be looking at the jackshaft side of things and maybe
the pegs. surprisingly enough the back of the frame only needed
half an inch or so of widening,just stood on it and bent it slightly.
i have a good derailleur lined up for it also. heres some pics,
one of the pics shows the underneath strap,everything is strap
welded, i dont want the bike snapping in half at 30mph. maybe a bit
overboard, but better safe than sorry. hopefully next week or the week
after she'll be a goer. still have to work out how to get a dual/tri gear
crank off a mountain bike on there too,that should be fun. :( lol.
the seat and everything else is last minute stuff, im going to try
and focus on the mechanics of it for now.
donnybrookechopper027.jpg

donnybrookechopper028.jpg

donnybrookechopper029.jpg

donnybrookechopper030.jpg

in this last picture you can see the shocks lying on the floor, i have lined up for the seat.

thanks for looking.
 
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Wheel building is piss easy, so many videos on th enet to show you how, free online spoke caluclators to tell you length of spoke to buy...heres an easy to follow tut from Sheldo Brown

Wheelbuilding

Might save you some money next time, akes less than 15 minutes to lace a wheel, use an old set of forks as a stand to true it..

KiM
 
might be easy for people who know, it but i know very little,so
its a fun learning experience. i have learned heaps working on this bike,
the fact i use cheap shi-ite isnt because i think its as good as pricey stuff, its simply
because i cant afford it,i know sealed bearings, and better gear, is,well,- better.
all i have is what i can scavenge,so far its just the cost of the motor,
my time, and what i owe my mate for doing it. dont know really know where that
came from,but on that note, i have decided to use a wheel hub off a mountain bike as
the jackshaft. i have been told not to use it, but i greased the bearings up good,cleaned it
all thoroughly, and i reckon she'll be sweet. just need to weld some sprockets on there
and weld it to the frame with some bracing.

today i did nothing really but stripped a wheel for its hub and took some more
pics. the lads had the bike with the motor on it, sitting on the racks. thought i would
snap some pics just for the sake of it.

instead of putting a mountain bike crank sprocket on there, i might drive the
standard bmx one from the jackshaft, and get another sprocket i have from a mountain
bike thats a bit smaller,and weld it on the outside.all will make sense when i get some
better pics next week.

my new jackshaft
donnybrookechopper034.jpg

donnybrookechopper031.jpg

donnybrookechopper032.jpg

donnybrookechopper033.jpg

all being well, next week i should have chains and gears starting
to be hooked up and things taking shape.i should have some more
time, and if i sell my car,more cash. what am i doing?.lol.
 
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