Are Anti Vibration Mounts Necessary?

Discussion in 'General Questions' started by sonny, Jul 5, 2008.

  1. sonny

    sonny New Member

    I am planning to build a MB with one of the kits that appears in a lot of the build pictures on this site. At least the one I am bidding on at ebay looks like them. While searching around I found someone who went to great engineering speak lengths to describe why the engine needs to be isolated from the frame with anti-vibration mounts that he sells. Has anyone had any experiencing with this or is their really not a problem with the vibration. I haven't seen any pictures of mounts that look anything other than stock.

    Thanks for taking the time to respond.

  2. eljefino

    eljefino Member

    The more mass, in one piece, that vibrates, the lower the frequency. Imagine the ground when a train or 18 wheeler goes by... low rumble.

    By tightly tying the motor to the bike frame, you're lowering the noise by spreading it out.

    If you isolate it, yes the frame vibrates less, but the motor and stuff attached to it... carby, exhaust, mounting studs... endure yet more hellish vibes, and the noise it makes is higher pitched, more annoying too.
  3. sonny

    sonny New Member

    Thanks for your reply. After I posted this I saw a thread on the site by the guy that has the kits on ebay. He was asking for memebers to buy it at a reduced price and post a review on the forum. I don't see where he had any takers.
  4. duivendyk

    duivendyk Guest

    It is not just a matter of noise,but also of destructive vibration being transmitted to the frame,this can cause fatigue fractures,the frame tube can look after failure as if it has been cut with a lazer,(at least in part),typically the fatigue fracture starts at a weak point in the crystal lattice and spreads insidiously until the tubing is sufficiently weakened so that a stress fracture completes the structural failure.Thin-wall structures like tubing are obviously more susceptible,they bend more readily and there is less material.The engine may vibrate but it is not likely to crack.Bear in mind that bicycle frames are not designed with resistance to metal fatigue as a major design consideration.Noise is preferable over a broken frame.It pays of course to isolate carbs by using flex mounting and using high grade components for critical parts like needle valves&seats.
  5. sonny

    sonny New Member

    Thanks for the additional insight. My concern was for the damage to the bike caused by the installation of the engine. Your reply makes me think that there is some need for worry and that maybe installing some form of dampening isolation is not such a bad idea.
  6. Pablo

    Pablo Motored Bikes Sponsor

    When I first mounted a HT engine in my MB frame the vibration was pretty nasty through the handle bars. Now that I have the shift kit and the rear mount has effectively been spread via a plate and two clamps to very much wider portion of the seat tube, the vibration and stress on the frame is much less.
  7. duivendyk

    duivendyk Guest

    Don't drill holes in frame tubes,the De Haviland Comet (the first operational jetliner) came apart because they had a small observation window in the top of the fuselage,to use a sextant, of all things,for navigation).That was the stress focus for a fatigue crack to develop.Bye bye Comet
  8. adamtheha

    adamtheha Member

    I would (from my limited point of view) suggest going with an anti-vibration kit if you will be riding longer distances. The more time you spend making your mounting rock solid, the less time you will spend later cleaning it up when a mount breaks. Also, your arms, feet and butt will thank you!
    There was an idea where you place a spring under a very long bolt that is drilled through the frame. It looks to me to isolate the engine just about completely, yet not be destructive to the engine. I can't remember where I saw it, sorry.