chain drive brompton folding bike

Discussion in 'Rack Mounted Engines' started by fireball_jones, Jun 29, 2009.

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  1. been working all weekend (again) thought i would start showing you guys what ive been up to.

    its still in process.

    and alot of thought was put into enable the bike to still fold. just undo the four engine bolts.

    anyway this is my lunch hour i post more stuff as i complete it

    what do you guys think?


    Attached Files:

  2. Happy Valley

    Happy Valley Active Member

    Looks pretty cool. What engine and and transmission arrangement are you using on that?
  3. thanks happy valley. yeap it was alot of thinking to get to this. its pretty much MY ultimate transport especially once proved reliable.

    im using a eho35 robin subaru, the choice of many motorbicyclists. the transmission is a 5:1 gearbox 8t custom made drive sprocket (made painstakingly one week end with a angle grinder a a template i drew if anyone know where i can buy one get one made or can make one for me that would be greatly apprcieted. :)) a 24 t stumley archer sprocket (the largest avalable ) which runs an internal geared hub with a total of .73 to 1.36 reduction/increase, of in 1:1 its calculated a 20mph ( i could get 27mph in first but im just to chicken sorry) however i think in the real world this is much lower due to efficency loses, of which i would be intrested to learn what peoples opinions are.


    i know some people may consider a full suspension 26" moutain bike "cool" but for me a bicycle that can fold as small as this, as ride as good, and potenialy be motor assisted is VERY cool.
  4. Happy Valley

    Happy Valley Active Member

    Thanks fj, just caught your update, nice work there. The black Robin threw me though, I have a few myself. You paint it?

    BTW, a motorized folder is definitely something I want to do one day great for traveling and that's cool.
    Last edited: Jul 11, 2009
  5. yeap i painted it only temporaryly (or however you spell that word :). other wise the engine sticks out to much, visually or in other words its very noticable. anyway in the states in good old kansas city where i used to live, engines are fine on bicycles if they are under 50cc (even had a police officer complament my tig welding on the frame mount i built:)) however here is the uk this are not so nice, so i have to be more secrative. ill take a photo becaue i also hid it within a pannier bag, with stratigic opens for the car and exhaust.
    ill post it up when i finish my tea.
  6. 5-7HEAVEN

    5-7HEAVEN Guest

    I mounted a Subaru engine w/1.125" friction drive on my folder bike. It ran very well but wouldn't fold anymore. 27mph was tops.

    Then I installed TLE 43cc Mitsubishi engine with chain drive on the Dahon. Now it folded, but was spooky fast.

    For safety reasons I abandoned the project, gave the bike away and transferred the Mits engine to a 26" girlie cruiser.:idea:
  7. Mountainman

    Mountainman Active Member

    nice -- heavy duty looking set up !!

    how sweet it must be to ride on that thing !!
  8. DetonatorTuning

    DetonatorTuning Active Member

    HI fireball,

    thanks for visiting my thread today.

    what you have done here is quite inovative. the internal geared hub up front is a wonderful choice for compact design and function.

    hows the weight of the engine out front affect the stability while riding ? is there any "torque steer" sensation ?

    getting many miles on it yet ?

  9. hello all,

    5-7 heavan i remember speaking to you about the friction drive and how it couldnt fold. tis a shame to have a folding bike an not have it fold. id like to see some of the photos of the chain drive folder. i remeber reading your thread but juct couldnt visualise it. Mine folds by removing the engine by the four bolts and the gearbox remains attache whilst not hindering the fold. and taking the engine off is benifical as im not worried about having the engine on the side etc. ill try and take a photo of how this is done asap.

    mountainman thanks for the complement. thats the first of any bikes ive built has been called "heavy duty" :)!!!! its a nice ride in my opinion but I like going at 15mph for long distances.

    DetonatorTuning no problem. thanks such gearing with the light 1:5 gearbox is only possible with small wheels so i have thought about this from the start of the design. as much as i would like to try a golden eagle kit the 1000miles per "rubber band" :p doesnt seem that much but really im more constrait by the fact they are not done it 16" wheels.

    as for torque streer thats for the lesson but i never even knew that existed. there is no effect i can for short spells 10-15 foot ride no handed.

    i have not put as many miles as i have liked yet im still trying to find a way to carry 4-5 times the gas/petrol tank capacity for longer rides :(, if anyone has suggestions im open to ideas. have have taken it around 40 miles in total test ride but really i want to use it for 100 mile plus rides in one day.
  10. finally got to 1000 miles 1035 to be exact :)

    well firstly ive made losts of changes and finished of alot of things,

    after first 30 miles a weld snapped at the strut or leg that goes to the motor (my fault poor penatration on weld...dam arc welder :( ) but fine sinse.

    i tried a stiffer rear suspension but my bum didnt like LOL

    i tried mounting the a one gallon tank on the back for really long rides works well be the bike didnt fold as small and dont look so nice

    biggest change was setting up the three speed BWR hub 300% range but probably a quater the weight of a nuvinci. correct me if im wrong :). but tend to use top gear which has good speed in the low revs and is quite quiet at that rev speed and use bottom for the hill :). and occasionally use top gear in high revs for chasing tractors :)!!!

    also ive linked up the front and back brake level to one handel 700 miles ago which works ...alright better with "kool stop samon pads"

    also painted the entire mount black

    i find the engine performs well but only get around 20 miles from a standard tank. is this what others get aswell?

    Im setting "Layla" up for a world the world tour so experimenting with differnt three speed front hub with disk brake.

    also fitted a hebie chain guard to cut down on maintainance with all the miles i do now.

    what i realise now that this bike can get me anywhere pretty much. yes it doesnt have full suspension but it folds soooo there! haha :)

    so next this to try out:

    1 three speed front hub with disk brake for low maintance, better braking, no rim wear an this eminiating the need to buy a 16" wheel in the middle of africa which my be difficult

    2 mounting a 1 gallon tank in space under seat.

    3 fit quick release adjustable steering stem

    ...eventually ill make a bag to fit inbetwwen the seat post and steering stem for camping equiment etc
    Last edited by a moderator: Dec 27, 2009
  11. well sorry for the delay,

    here are some photos.

    to busy riding less busy typin :)

    Attached Files:

  12. lowracer

    lowracer Member

    I really like what you've done with the Brompton.
    Motored & portability is something we don't see often but is definitely an excellent combination.
    Is there any problem containing the fuel once its folded up & laid on its side?
    Thanks for sharing,
  13. Thanks Lowracer,

    Is there any problem containing the fuel once its folded up & laid on its side? from oer 1000 miles, more than a years use...none from my experience, i do think it might but have never had a problem with it, so i stop worring. still have a problem running it in the cold though.

    i think our bikes are certainly oppersite sides of the scale in terms of use, but certainly very close in terms of inventivness/design and most importantly FUN!

    Safe ridding Sir!
  14. 5-7HEAVEN

    5-7HEAVEN Guest

    My Dahon folder bike is long gone; too squirrelly for my speed.

    This was bolted onto the top of my Staton friction drive, and gave long range.
  15. 5-7 heaven,

    Thanks for the recommendation. I solved this problem by having a pannier bag with a onegallon tank :) works out generally 130 miles i think, just have to stop every twenty miles to fill up. i would say it helps me to stop and apprciate the views smell the roses etc, but this weekend the farmers were out spreading manure i think so i was not smelling to many roses :).

    illl post a photo next time.
  16. Silvaire

    Silvaire Member


    As you have gone over 1000 miles so far, how has the little 5:1 gearbox held up?

    Do you notice any gear whine above the sound of the engine/chain/tire/wind noise?

    I'd like to use one of these gearboxes with a Subaru EH035 on a project, but the gears look so tiny. I have bought a couple of used scooters with these gearboxes on them, but by the time I got them the gears in both of them were badly worn (and dry or nearly so at the time I got them). I have a nearly new 5:1 gearbox around too, but I am just wondering if I should even bother to try working with it.
  17. hi Silvaire,

    I have dont noticed any problems with the gearbox, however I am gentel on it. oil it well, and having a 3 speed hub reduces forces on the gears. im away nxt week but will send you a photo of inside the casing when i return to "civilisation" :)
  18. eastwoodo4

    eastwoodo4 Member

    ive seen them gear boxes on pocket bikes a lot.there pretty indestructible.

    will your bike fit in a suitcase?that could be really cool.i imagine $100 will take you on a bus anywhere in the country.then you can bike around when you get there.