Cold bending 1 piece cranks?

Discussion in 'Motorized Bicycle General Discussion' started by wayne z, Dec 20, 2011.

  1. wayne z

    wayne z New Member

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    Does anyone know of experiments with cold bending offsets in 1 piece cranks for 4 stroke motor clearence, with a press or other methods?
    I have some ideas for a pair of bending forks to do it without removal from the bike. Work similar to a tubing bender but much stouter.
    Just want to know if anyone knows wether they will bend or snap, if given enough pressure to bend without heat.
    Thanks, Wayne
     
  2. 2door

    2door Moderator
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    Wayne,
    Typically, if you go slow and take your time the metal will bend without breaking. Cranks are not made of extremely hard steel that would be prone to failure with careful bending. I've seen cranks on bikes that were run over by cars and they were bent way more than you'll need and they didn't break. I would suggest to concentrate the bending force so that you aren't compromising the bearings. Go for it and please share your idea/photos for a bender that others might find interesting.
    Tom
     
    #2 2door, Dec 20, 2011
    Last edited: Dec 20, 2011
  3. wayne z

    wayne z New Member

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    OK,'ll be ready to try to bend one in a couple days. I built the hub fork tonight. 2 pieces of 1/2 x 2 1/2 x 6 bar stock with 2 holes to put 5/8 pins, one thru the hole inside the pin that drives the chainring and one opposite on the outside of the crankarm. the other end of these plates are drilled to take a piece of 3/4 x 2 x12 barstock.
    A 4 foot cheater pipe will be stuck on this, and positoned against the ground to hold up the bike and take the bending pressure of the other bending tool, similar to the way a hand operated conduit bender works.
    The other tool will just be a piece of 1"x2 1/2 x 12 stock with a 7/8" hole to recieve the crank leg, and a cheater pipe on the other end. The hole's edges will be rounded to keep from marring the crank when bending pressure is applied.

    Then the tools will be re-positioned farther down the crank arm, to add the offset bend in the opposite directon, near the tip of the crank arms. Might hafta puts slugs made from cut off pedal studs in the holes to keep the holes from distorting when bending so close.
    This is only theory, until i try it. I'll post some pics if it works or not LOL.
     
    #3 wayne z, Dec 20, 2011
    Last edited: Dec 20, 2011
  4. sportscarpat

    sportscarpat Bonneville Bomber the Salt Flat record breaker

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    I have bent a lot of one piece cranks, not always on purpose! I have found that trying to hold on to them well enough while bending in the spot you want can be difficult. Heat at the point of bending makes sure it will bend where you want it to. Also very difficult to keep the pedals on the same plain once your done. Sometimes it goes well and other times you mess with them for hours. Easier to just buy a wide offset three piece pedal crank.
     
  5. wayne z

    wayne z New Member

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    OK, I bent some cranks on a Huffy tonight with my bending bars.

    They came out real good. Only took about 5 munites per side.

    I made the first bend, near the hub with the 4' static bar on the floor. I then applied force repeatedly to the bending bar, and got a pretty steep angle that measured 24" from floor to cheater pipe end, static.(no pressure but gravity on the cheater pipe.)
    I then reversed the static bar, added the moveable bar to the crankleg at the tip, and stuck a 3/8 carriage bolt in the pedal hole, as a stop pin, and pulled both bar tips close to the crank arm end and eyballed the reverse bend(pushing bars apart, to parallel the pedal holes with the bike's frame.
    I then repeated the process on the other side. Here's the results.
    IMAG0131.jpg

    IMAG0135.jpg

    IMAG0132.jpg
     
    #5 wayne z, Dec 21, 2011
    Last edited: Dec 21, 2011
  6. killercanuck

    killercanuck New Member

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    Wow, nice result! Great idea on the bender.
     
  7. leadfarmer

    leadfarmer New Member

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    Very nice, you've got the touch
    or beginner's luck:)
     
  8. 2door

    2door Moderator
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    Wayne,
    Thanks for sharing your bending tool/method with us. Congratulations.
    Have fun and ride safe.
    Tom
     
  9. mapbike

    mapbike Active Member

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    As Wayne has shown here...

    " Where there is a WILL there is a WAY "

    " Improvise Adapt and Overcome "

    Nice job.

    Peace
     
  10. dmb

    dmb Active Member

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    very nice!
     
  11. wayne z

    wayne z New Member

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    Thanks guys for the compliments. Sometimes I get things done because I didn't know I couldn't LOL
     
  12. midwestmayhem

    midwestmayhem New Member

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    Nice job, I like the idea on the jig

    I've had to staighten some bent cranks in the past due to accidents. Alway's layed the bike down on some 4" blocks, making sure the other side of the crank was supported, and slid a piece of water pipe over the end of the crank. I'd use one hand towards the end of the pipe, pulling up, and the other down were the pipe was slid onto the crank, pressing down. Or both hands on the end of the pipe, pulling up, and one foot or both feet, if possible, were the pipe was slid onto the crank. Did my best to avoid damaging bearings. They came out straight, and the bears still good.
     
    #12 midwestmayhem, Dec 23, 2011
    Last edited: Dec 23, 2011
  13. 2door

    2door Moderator
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    Wayne, you're like me. Never ever tell me I can't do something. I'll be sure to do it then :)

    I remember a pro street rod builder telling me I couldn't put Volvo calipers on early Chevy spindles. I asked why not and he said, "Cause they don't make a kit for that."

    Ha, showed him. :)

    Tom
     
  14. Dwight Pierce

    Dwight Pierce New Member

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    Thankyou for sharing this information I will be bending mine soon.

    Dwight
     
  15. dracothered

    dracothered New Member

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    Would adding heat help it bend easier or do you think it is not needed?
     
  16. wayne z

    wayne z New Member

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    Adding heat definitly makes it easier. No special bending forks and back up forks needed. I had no way to heat minr so I experimented, successfuly, with cold bending.
     
  17. tooljunkie

    tooljunkie Member

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    there's heating and then there's overheating.
    wayne successfully bent without heat,i think a low heat would help,not red or orange heat.it may cause it to become brittle unless you cool it very slowly.
     
  18. dracothered

    dracothered New Member

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    Unless you dunk it in water or oil after heating and bending it they will not be hardened. Cold bending will work as Wayne showed, but anytime you cold bend metal you are introducing allot of stress.
     
  19. wayne z

    wayne z New Member

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    Yes, it don't take a lot of heat to do the job. The times that I did use heat, I wrapped the BB in wet rags, and heated the crank until I could just barely see some redness then bent it about 35 degrees. then heated the tip about an inch away from the pedal threads and reverse bent it until the hole was perpendicular to the bike.
    Afterwards of doing one side, I ran water on the BB some while the crank cooled down. Then I did the other side and cooled it again. Then, I heated and bent the tips.
    With low heat like this, you can polish the blue off the chrome with steel wool and hardly tell that it was heated.
    Unless you're real good at eyeballing the angles, I would suggest that you should make a plywood or cardboard template with drawn lines, that you can hold against the frame to sight your bends to.
     
  20. dracothered

    dracothered New Member

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    Cool and thanks for the info, I will put it to good use as I will need to bend my crank arms for clearing the 2 stroker I'm going to be putting in it.
     

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