Exhaust Two Questions: Exhaust and RPM

Discussion in '2-Stroke Engines' started by mrsaxman99, Dec 4, 2006.

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  1. mrsaxman99

    mrsaxman99 Guest

    1) What is a good/safe way to bend the exhaust pipe. I need a good 15 degree bend on it to get it out of the way of my left pedal. I know you need to remove it from the engine, but then can you just bang it with a hammer???

    2) has anyone figured out a good equation for getting accurate engine RPM based on Speed (using a 26" tire and 44 tooth sprocket)? I will probably go to the trouble to figure it out exactly once I get mine up and running.

    Thanks everyone!

  2. motorbicycle

    motorbicycle Guest

    About the muffler, I just put it in a vise and pulled and pushed on it with my hands. It is fairly weak so it should bend. Keep doing this until you get the right bend.
  3. davidsis

    davidsis Guest


    I do not get the RPM question. seems like you only have one selection High. RPMs on mine with 26" tires at 25 mph is crazy high.
  4. gone_fishin

    gone_fishin Guest

    do not bang on that pipe with a hammer, any place you ding it is gonna rust much faster (inside too)

    use wood blocks inside and outside your curve, and have patience, work the bend a lil at a time, moving slowly along to avoid a sudden kink...that's my 2-pennies worth 8)
  5. bird

    bird Guest

    heat the pipe up with a propane torch while its in a vice and then bend it. it works alot better i did this on one of my pipes. the pipe might blue where u heated it up tho.
  6. Dr. J.

    Dr. J. Guest

    To get an accurate RPM indication, you might consider the Sportech Mini-Tach. You can get them for two or four stroke motors. Search the Internet and look for the best price. I had one on a Cushman a few years ago and it worked great.

    Dr. J.
  7. mrsaxman99

    mrsaxman99 Guest

    Cool I'll try heating the pipe.

    Audgidog, use wooden blocks inside and outside the curve, and then bend by hand I assume you mean?

    Davidsis, I am talking about simply using bicycle speed to determine RPM. you can do the math...20mph -? bicycle tire rotations per minute, then just divide out the ratios till you get to the crank of the engine. Do this so you can just have your speedo on your bike and know that 20mph = 4k rpm, 25mph = 5k rpm, etc...

    anyone know the gear ratio on the crank side of the engine...when I briefly looked at it, looked close to 3:1...i'll pull the cover and count teeth.
  8. gone_fishin

    gone_fishin Guest

    yup, using heat with wooden blocks should make for a fairly easy & clean bend 8)

    don't forget to wear some gloves :?

    hehe, you're lil RPM/science project reminds me of a technical drawing i did for physics in high school...i used pulleys, gears, levers, etc...had about 30 or so components with a mechanical mad-vantage of something like 28,000:1 :p
  9. davidsis

    davidsis Guest


  10. bird

    bird Guest

    the oldschool mechanical speedometers that hook up to the front wheel also tell you how many rpms your bikes running. they are cheep to like 20 bucks


    Ok little trade secret!! If you want to put a decent bend in your pipe without causing damage plug one end fill it with water and drop it in the freezer over night. The ice inside will support the inner walls of the pipe and stop it kinking while you bend.
  12. daveinblythe

    daveinblythe Guest

    I dont know what kind of tools you have to work with but if you have an emt bender that would work best and yes take it off the motor those little 6mm studs wont take the turning presure off bending the tube but you will need to get some hi-temp paint cause the crome plating is going to crack and chip when you bend the tube.....i've found that just playing around with an emt bender(20 bucks at most hardwhere stores)and 10 foot of 1" emt (electrical conduit) you can make some realy cool bends for exhaust pipes
  13. ringal

    ringal Guest

    Engine speed

    Joined: 30 Sep 2006
    Posts: 12
    Location: Perth Western Australia
    Posted: Wed Dec 27, 2006 4:44 am Post subject: Sprocket and engine RPM


    Just for your info I crunched the numbers and based on a 26" bike wheel here are the results......

    At 30 MPH with 44 tooth sprocket engine RPM is 7,205
    At 30 MPH with 36 tooth sprocket engine RPM is 5,895

    And if the engine would do 10,000 RPM with 36 tooth sprocket the road speed will be 50.9 MPH

    Regards Al
  14. srdavo

    srdavo Active Member

    Nov 4, 2006
    Likes Received:
    I read about a guy filling tubing with sand....then he wedged it between a couple trees and made his bend. so I totally buy the ice trick. we're getting into some McGuyver stuff here.
  15. apratt

    apratt Guest

    I can see the sand trick but not the ice. To me the ice would not bend but would break up, maybe it does work. Just seam the sand would be easier.
  16. srdavo

    srdavo Active Member

    Nov 4, 2006
    Likes Received:
    prolly don't matter if the ice breaks....it is filling the space.
  17. davidsis

    davidsis Guest

    Ice and sand

    I have heard that balbarings are something that I heared can be put in a pipe. seems like ice would brake.
  18. gone_fishin

    gone_fishin Guest

    it will break, but since the crushed-ice still has nowhere to go, the pipe will have the "backpressure" that helps to prevent kinking 8)

    after the job is done just use the crushed-ice for a margarita or something :evil:
  19. Steve

    Steve Guest

    There's too long of a story behind it, but I replaced the pipe on my exhaust with 3/4" conduit (it was the same size) and used a conduit bender to bend it.
  20. gone_fishin

    gone_fishin Guest

    cool, got pics?

    go have a margarita anyway....you earned it :)