possible interesting idea.

Discussion in 'General Questions' started by fasjake, Oct 12, 2016.

  1. fasjake

    fasjake New Member

    Although it would eliminate the use of pedals... i had a brief thought in my head involving two right hand crank arms from a vintage cotter pin style 3 piece crankset. Cut the crank arms off, leaving you with just the chainring. Throw those on right and left sides. Connect engine sprocket via chain to the left side, effectively powering the right side to be connected to the rear cassette. I want to try it..... does anyone see any problems with this im not thinking of?

  2. Jonj57

    Jonj57 Member

    I was thinking the same thing as I dont actually run pedals on my bike anymore. The only issues I see are alignment honestly, it'd be hard to align it L/R on the BB and it might not be able to clear the case on the engine so you'd need to fabricate a custom frame mounted tensioner.

    I'd say durability might be an issue but a BB swap is easy and quick with the sealed type and they're pretty cheap to replace. I could get like 5 BB's for the price of one jackshaft free wheel honestly
    fasjake likes this.
  3. KB_UK

    KB_UK Member

    I don't see why you'd need the cottered cranks for this. Could do exactly the same stunt with square tapered cranks.

    The problem is of gearing. On our 2stroke engines you have a what, 10 tooth engine sprocket, to a 44 tooth wheel sprocket. So you're gearing down. A pedal transmission is the opposite, you gear up, because pedalling is much slower than even an engine idle.

    It's easy enough to get a 44 tooth chainring for your left hand side on ebay. The problem will be finding one small enough for the right hand side... If you have a 28T lowest freewheel cog then you'd need a 28T chainring to make your 1st gear match the standard gearing of a normal gearless engine setup. You could go lower by fitting a bigger left hand side chainring, 52T in particular are easy to get because of all the millions of bikes that had them in the 80s. Bigger than that is harder to get.

    Just wondering - where do you put your feet without pedals?
  4. fasjake

    fasjake New Member

    The old cotter style cranksets would be nest for this i believe because the crank arm is raised away from the chainring making it easier to cut. Also, every other style crankset i know of has more balk to the crank arm making it harder to achieve a good rotational balance.
    As for gearing, the options are limitless(within reason). The project on which this "wacky" idea would be used is actually a single speed and would not utilize a rear cassette or derailleur. I want the right hand drive would look cleaner, not interfere with the left handed disk brake system, wouldnt have to deal with compromising the integrity of my wheel with the awkward rear spoke clamp sprocket setup, and take care of the 3.25 tire vs chain dilemma.
    Foot pegs welded to the frame is easy enough and would be preferred for the project i had in mind.
  5. KB_UK

    KB_UK Member

    With both square taper and cottered of good quality you have the ability to unbolt the chainrings from the spider for cutting the arms off. The problem with cottered, though, is that it's harder to get the matching chainrings because of the different standards BCDs and bolt patterns, plus sheer age of the parts. And also the matter of ruining vintage bike parts.

    As a singlespeed it makes sense I suppose but you're still limited by having to find a chainring the same size, or smaller, than your rear wheel's cog. 28T is the smallest I've ever seen, and that's a four bolt MTB crank.

    Do you have a pull start engine? Obviously pedalling is out, and can't push start either because of the freewheel coasting.

    What might be better to look at is hubs that can take the engine's big wheel sprocket. I've seen some out there.
  6. fasjake

    fasjake New Member

    A big heavy duty balloon wheel flip flop hub would be ideal.
  7. Jonj57

    Jonj57 Member

    I've done multiple things but as of right now I use Harley Cruiser clamp on foot pegs that flip up and down, the simplest one was just put both crank arms facing down and use it that way. It's only viable that way if you have short crank arms though.
  8. FurryOnTheInside

    FurryOnTheInside Active Member

    SBP sell the freewheel crank set separately. I think SBP do a 24t that has holes to bolt it to their White Industries freewheel. They also do a 130mm BCD five arm spider which can be bolted alongside the 24t. We can buy a 56-60t single speed track bike chainring or a 8/9 speed time trial chainring which will work with a 1/8" chain. Either can bolt to the 130 BCD spider which can also act as a spacer separating the two chain lines. The engine turned backwards and retimed to run in reverse (by just reversing the magnet, adding a new keyway?) would power the large chainring and the reduction is all taken care of on that one side.
    You still have pedals and some ultra low gears if you need to pedal home. No jackshaft and you can still pedal the uphills if the engine breaks down.

    *Not so good if the ride home is flat.
    Last edited: Oct 14, 2016