seat vibration

Discussion in 'Frame Mounted Engines' started by jayjmarlo, Mar 10, 2013.

  1. jayjmarlo

    jayjmarlo New Member

    My seat seems to be vibrating a little too much to comfortably ride long distances at full throttle. It seems to have gotten worse recently. Any idea how I could figure out where it is coming from? The engine mounts are solid I wrapped the frame in thick leather under the mounting hardware. I'm running the Chinese 66cc 2 stroke on a mountain bike.
     

  2. wheelbender6

    wheelbender6 Well-Known Member

    if you have a quality made chromoly steel bike frame, they can be very stiff, and you may have to learn to live with the vibration. Aluminum frames can also be very stiff. The steel frames made from thicker, lower grade, tensile steel seem to absorb vibration better.
    You may be able to try a suspension seatpost to damp the vibration.
     
  3. jaguar

    jaguar Well-Known Member

    Fix the source of the problem instead of trying to cope with it.
    Use a lighter weight wrist pin and get a CDI that retards the spark at high rpm.
    Click on my signature link to read all about it.
     
  4. Fabian

    Fabian Well-Known Member

    I completely agree because my next door neighbour has motorized an old lower spec steel framed bike and the vibration levels are massively reduced over my bike which has an aluminium frame; and we both have identical engines.

    I've tried to get a specialist bespoke frame maker who only works with heavy section crome molly round tubing to copy the design of the GT LTS but incorporate disk brake mounts.
    Unfortunately he had a heart attack when looking at the rear suspension linkage system and flatly refused to take on my project, which was disheartening as i principally wanted the vibration reducing qualities of steel.
     
  5. crassius

    crassius Well-Known Member

    don't worry, if you keep riding at full throttle the vibration will go away as soon as the bottom end bearings blow out (think putting your car in first gear and driving with the gas to the floor everywhere you go)

    when riding, look for a 'sweet spot' in sound & vibration at about 2/3 of top speed - that's your cruising speed
     
  6. jayjmarlo

    jayjmarlo New Member

    Makes since, do you all mostly cruise at 2/3 throttle for long distance rides?
     
  7. crassius

    crassius Well-Known Member

    depends on the bike as to exactly where the sweet spot is - when it starts to get too loud or vibrate too much, drop the throttle back just a bit

    you can get thousands of miles out of it if you treat it well - just a few months if you don't
     
  8. wheelbender6

    wheelbender6 Well-Known Member

    At what speed do the vibrations get bad? Maybe you can simply get a smaller rear sprocket to reduce engine rpm (and vibration) at your cruise speed.
     
  9. jaguar

    jaguar Well-Known Member

    god, someone please remove me from this iseless conversation.
    Would any of you accommodate a bee if it was buzzing around inside your car? Hell no, you would stop and let it out. You would solve the problem. You wouldn't run inside to make a bowl of sugar water to set inside the car to placate the bee.
    Fix the problem (which isn't the frame or the motor mounts)!!!
    what crap most of ya'll put up with. it totally amazes me. a little effort and a little beer money solves these little problems.
     
  10. Bob K

    Bob K New Member

    I love your sense of humor!
    ( y'alls bowl of sugar water):grin5:
    Keep 'em comming!
    Seriously though, how else can you convey the same message repeatedly?
    ( well humor works for me! )
     
  11. jaguar

    jaguar Well-Known Member

    well I'm glad you're taking it that way. I just don't know how to get people thinking the right way after doing everything but doing it for them. Maybe that's what they are waiting for. I tell the latino women here that they are ruining their children for life by giving them all the love and attention they can stand and doing everything for them. They wind up as adults waiting for others to do things for them. totally spoiled good for nothing consumers.
    Think
    Decide
    Act
     
  12. grinningremlin

    grinningremlin Active Member

    That's kind of sounding like America these days.
    To the OP, either
    A: take Jaguar's advise, learn a little something, and save a bit of $$ in the long run,... or
    B: buy something like those cranecreek thudbuster ( I think that's the name) suspension seatposts, I think the elastomers would negate some of the vibro getting to you.
     
  13. HeadSmess

    HeadSmess Well-Known Member

    welding the motor mounts on solid works for me. seems to make a loose rattly motor into a solid little runner. let the frame absorb the vibrations!

    putting anything squishy between clamps and frame is pointless, if not counter productive from my way of thinking.

    one. leave the clamps loose enough so the squishy stuff can squish. the motor then twists on the frame as theres only two mounts and an offset load. ie, the chain...

    two. do the clamps up tight so that the squishy stuffed is all squished up. um...? all squished up....

    "isolating" the motor simply lets it vibrate more... leaving it to shake around randomly.

    at least in my experience it does...

    pffft, balancing single cylinder twostrokes.... :jester:
     
  14. jaguar

    jaguar Well-Known Member

    without a lighter wrist pin and a Jaguar CDI you really just don't know what you're missing. Laugh as you will about "balancing", the jokes on you. The imbalance in your motor wears out the conrod and crank bearings prematurely and limits its ability to rev since it has to fight against the imbalance.
     
  15. Fabian

    Fabian Well-Known Member

    I was under the impression that a single cylinder engine "cannot" be perfectly balanced for primary vibration; only the inherent vibration being tuned to a different rpm zone by altering the counter balance weight or altering the reciprocating weight.
     
  16. jaguar

    jaguar Well-Known Member

    Headsmess, you're busted! This is what you wrote in another post: "lost count of how many times ive lost a mount". On the other hand, I never lose a motor mount. Why? Because I believe you can fairly well balance a 2 stroke engine and you do not. I did the 2 essential steps to get rid of most of the vibration and you have not.
     
  17. jaguar

    jaguar Well-Known Member

    Fabian that is true, but we're not talking about "perfect". What happens is the offset force throughout the rpm range is not linear on a graph, whereas the counter force by an "imbalanced" flywheel is linear. Only if the two graphs were linear could a match be made for perfect balance. But to throw your hands in the air and just give up is nonsense. A good compromise can be had so that thru the whole rpm range there is no excessive imbalance between the two forces.
     
    Last edited: Mar 13, 2013
  18. Fabian

    Fabian Well-Known Member

    How does the crankshaft (on a single cylinder engine) self balance the counter weight force vector when at 90 degrees to the piston?

    I'm just going to throw my hands in the air and reduce vibration by reducing engine speed.
    With torque boosting measures like a reed valve intake and a higher compression cylinder head and a Jaguar CDI and a SickBikeParts shift kit, you can keep the rpms below 3,500 and still have reasonable road speed as well as minimising vibration, not to mention significantly increasing engine life.
     
  19. Fabian

    Fabian Well-Known Member

    Holy heck, it seems like someone has been busted big time.
    We need a Jerry Springer style, trial by jury, complete with scantly clad women and jurors ready to feed the accused into the lion pit (filled with a Jaguar that has not eaten in a month); using only a plastic spatula as a weapon and a trash can lid as shield.

    Now will somebody pass me a beer and a side dish of cheese, crackers, dips, cabana and a decent red wine.
    I just want to sit back for the show :evilgrin:
     
  20. jaguar

    jaguar Well-Known Member

    The force is upward when the piston is at TDC which is counterbalanced by the flywheels being heavier on the side opposite of the connecting rod pivot (due to holes around that pivot)
     
Loading...