Still want to argue about rubber mounting?

Discussion in 'Mounting Techniques for Bicycle Motors' started by maniac57, Jun 30, 2014.

  1. maniac57

    maniac57 Old, Fat, and still faster than you

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    [​IMG]
    Look carefully.
    See the white pad between the mount plate and frame under the Ubolt?
    Notice the flattened frame tube? Caused by overtightening to try and stop inevitable engine movement caused by rubber.
    Notice the visible distortion and damage on the chunk of downtube still visible?
    Also notice the damaged area (paint worn off where engine rubbed) clearly visible on the broken section of seatpost tube from VIBRATION causing ENGINE MOVEMENT.


    DON'T USE RUBBER OR ANY TYPE OF COMPRESSIBLE MATERIAL IN YOUR MOTOR MOUNTS.
    *Wipes spittle off monitor screen*
     
  2. xseler

    xseler Active Member

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    Looks like a 'won't let me type the appropriate thing' moment.............
     
  3. Davezilla

    Davezilla New Member

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    I agree... Solid mounting is the way to go, and I noticed a LOT less vibes were transfered after I welded mounting tabs to bolt my engine directly to the frame, If you can move the engine around with your hands after it's installed it's going to vibrate badly and eventually saw thru the frame tubes like the pics above
     
  4. 2door

    2door Moderator
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    Ditto, about forty times. Although Maniac's photo example is worst case scenario, its is almost inevitable that something bad is going to eventually happen with a rubber mounted engine.

    We'll get the arguments that cars and motorcycles use rubber mounts but that argument doesn't hold up because cars and bikes use a steel/rubber/steel sandwich style that removes engine vibrations from the mounts and fasteners. Not true when folks try to stick rubber between the engine and the frame then use the stock mounting parts over it. Totally different concept from automotive/motorcycle/aircraft/boat/ engine mounts.

    Thanks, Maniac for helping to dispell an old myth about "reducing vibration" thru rubber mounts. Any builder thinking of using rubber/resilient material, needs to read this one.

    Tom
     
  5. GearNut

    GearNut New Member

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    Holy cow man! That's a sad ending for a good bike frame...
    I hope the rider was not hurt when it failed!

    So..... What are you going to do now? make it into a drop loop frame?
     
  6. Kioshk

    Kioshk Active Member

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    It's worth noting that this build's muffler shoulda been secured as well; that free-cantilever can really amplify vibes.
     
  7. Pablo

    Pablo Master Bike Builder & Forum Sponsor

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    Cool bike bro. How does she ride?
     
  8. wret

    wret Member

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    Maniac, can you enlighten me? What is it about using a dampening material that is causing the failure? Is it just due to way its being used inhibiting the the stability of the mount?
     
  9. sboricic123

    sboricic123 New Member

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    The bike frame looks like scrap metal now. I think the picture should be "sticky" on the mounting forum for other new riders.
     
  10. Desert Rat

    Desert Rat New Member

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    I'm not maniac but the flexible material aka rubber sets the motor up to rock
    back and forth creating more vibes not less, steel to steel solid is the only way
    to reduce that and one thing I've never heard brought up is seats with springs
    Where a small vibe can be greatly amplified IMHO
     
  11. Toothy

    Toothy New Member

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    Whats the story behind the pic? Apart from using rubber of course.
     
  12. crassius

    crassius Active Member

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    Yep, that's what happens - seen it with bare metal mounts too, so always put a piece of PVC or hard leather there.

    Fixable tho with an old seat post to fit inside, then put bolts thru at top & bottom
     
  13. BigBlue

    BigBlue New Member

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    Rubber mounts are just like having an Oscillating (vibrating)saw between your legslaff

    Chris
    AKA: BigBlue
     
  14. JOBAfunky

    JOBAfunky New Member

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    Ya I ended up using leather on mine and it seems to be working all right. What about those 1 inch thick purpose made rubber mounts? Anybody ever try using those?
     
  15. 2door

    2door Moderator
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    NO RUBBER is what we're saying. I know there is at least one engine vendor who is selling rubber mounts. He should be ashamed of himself. And he should read this thread.

    Tom
     
  16. scotto-

    scotto- Custom 4-Stroke Bike Builder

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    Sorry to say but I can't agree entirely with this, the reason being is I use a very thin plastic (not like PVC) or urethane between certain engine mounts and tighten it down to where it's less than .005" thick and have no problems.

    I won't get into telling you why I do this, but it works for me.

    You don't want a cushy type rubber of any thickness type mount for sure, when it comes to mounting your engine to a bicycle frame.
     
  17. biknut

    biknut Active Member

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    I'm not buying it either. the Atomic BB is 3 1/2 years old, over 2000 miles, and 2 engines, plus alloy frame.

    Plenty of frames break when the motor is solid mounted too. The problem is not the rubber, it's poor engineering on the builders part.

    Front motor mount is a rubber hockey puck. I made 3 other bikes with the same front mount and none of them have had any problems from it.

    [​IMG]
     
  18. crassius

    crassius Active Member

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    most rubber will dissolve a bit after being exposed to fuel, and most rubber is easily cut through by vibrating metal - that said, there *may* be a kind that will work, but why bother taking the chance
     
  19. maniac57

    maniac57 Old, Fat, and still faster than you

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    The problem is any movement AT ALL in a mount concentrates all the vibration on whatever is moving, be it a standard ubolt or any type of clamp.
    This forces the bolts or clamp to absorb and transfer ALL the movement.
    The PROPER way is a ROCK SOLID mount which distributes the vibration from the engine out into the frame where the tubing and triangulation spreads all the movement and absorbs it.
    Allowing the mount to move forces ALL the movement to one point where bad things happen.
     
  20. maniac57

    maniac57 Old, Fat, and still faster than you

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    They story is there was no rubber in this bike. It was pure vibration and poor huffy tubing.
    I can see the wear on the seat tube where the vibration had been sawing away at the tube, as well as the flattened and distorted down tube. This was caused by a poor fitting, loose motor allowed to move FAR too long.
    While this failure was not rubber related, Rubber simply makes this happen faster by concentrating all the vibes on the mount.
    Don't bother ranting about how rubber works and your bike is proof guys...You know who you are, and this is not meant for builders like you guys anyway.
    It's meant for people still learning.
    Experienced builders use rubber mounting properly IF they use it at all..
    My point is that for 99.99999% of the bikes out there, and ALL the newcomers to the hobby, rubber is a BAD IDEA.
    Just my opinion.
     
    #20 maniac57, Jul 1, 2014
    Last edited: Jul 1, 2014

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