Bad vibrations

Discussion in '2-Stroke Engines' started by Hajuu, Apr 4, 2010.

  1. Hajuu

    Hajuu Member

    Hey guys

    I've just finished my second build a few days ago, and its already got probably 100km on it.

    However i've just started noticing something, there is seemingly suddenly a LOT of vibration. Maybe i'm just going faster than I imagine but it doesn't feel like im going any faster, it just feels unbelievably vibratey.

    So much so that it's almost unusable at its max speed as the handlebars are very hard to hold onto.
     

  2. motorpsycho

    motorpsycho Active Member

    the rims could be bent, tires could be out of round or have flat spots in them, wheel bearings could be loose, headset bearings could be loose...there are a lot of things that will cause a vibration.
    yes, tires can be out of round, even when brand new.
     
  3. Hajuu

    Hajuu Member

    Hm, i'm not familiar with that phrase 'out of round'. Does that mean like, isn't propperly round?

    If I take the bike to a bike workshop what are my chances of getting the rear wheel tuned with all this kit on the bike?
     
  4. professor

    professor Active Member

    Really, this is simple stuff that you can do.
    Go to youtube and punch in bike rims or something like "Lacing rims" and learn to do truing. All you need to do is buy a spoke wrench and they are very inexpensive.
    Make sure your motor is tied down good. Plus check what Motorpsyco said.
     
  5. Al.Fisherman

    Al.Fisherman Active Member

    One of the first things one should do before anything else after choosing a bike is to flip it over and spin both wheels. I've bought 3 NEW bikes and not one of them were the wheels true. I now do it in the store to see how bad it is and choose a different bike. To true a wheel is very easy but at times can run ragged. A very bad out of round wheel (notice I'm talking WHEEL) can take some time to true up. There are a number of sites that take you through the process of truing a wheel on the internet. Now for out of round...both the wheel and tires can be out of round. The best way to check this is first true the wheel WITHOUT the tire, once the wheel is true install the tire and spin. A out of round tire will while spinning look like the tire is moving up and down while looking at it from the tread. Today, out of round tires are not as common as many years ago, and I'm talking when I was 15-16 and we used nylon (auto) tires. Back then to true a out of round tire they would mount the tire, balance it (No spin balance back then just bubble balance) and shave the high tread off the tire.
     
  6. Hajuu

    Hajuu Member

    Some good tips there, i'll check it out - I do also feel a kind of slight 'bump bump bump' at high speeds if I put weight on the seat (rear wheel) instead of the pedals, but it's very slight.

    Thanks for the tips anyway, i'll let you guys know how I go.
     
  7. motorpsycho

    motorpsycho Active Member

    actually, semi truck tires can be out of round (and i'm not just talking about re-caps or re-treads either)
    I have seen brand new semi truck tires so badly out of round that they will shake the whole truck bad enough to make the driver think he has a busted axle, bad wheel bearing or a bent rim.
    Bicycle tires can also be made out of round like al said.
    yes, this out of roundness used to happen qhite often on the old bias ply nylon tires. but today we have nice radial tires, and i don't thin it happens too often with those.
    But most semi truck tires and bike tires are not as sophisticated as radial car tires are, so there could be some casting /molding mistakes here and there. I don't think bike tires need to be made with the tight tolerances that car tires do.
    after all, most bike tire mfg's probably think " the bikes that these tires are going on wil never see over 10-15 mph, so a little wobble won't hurt."
     
  8. Al.Fisherman

    Al.Fisherman Active Member

    Same thing with the wheel itself...at 10-15mph you'd never realize the wheel itself isn't true. Kick it up some and it's very noticeable especially when someone is following you. I'd suspect this would raise all kinds of heck with the bearings over a period of time.
     
  9. Hajuu

    Hajuu Member

    On a side note, I realised the simplest solution for the time being (going to attend to it propperly today now I have some time off) was some big foam handlebar mounts, big enough even to go over the throttle.

    The vibration at max speed on a flat (WOT - not gaining any more speed) was at times so unbearable to my hands that at one point I actually believed myself to have a fractured knuckle/finger it was so sore. (all good though).

    I'm thinking some additional vibration is being caused by;

    1. After about 100km, the mounting bolts have come slightly loose
    2. As a side effect/possibly always, the engine may have twisted a few degrees, making the chain not mesh with the gears propperly
    3. A slight wobble on the wheel caused by either a buckled rim or 'out of round tyre' as you guys are saying, exadurated by speed - possibly also causing a partial rub with one side break pad unnoticable at such speeds.

    Going to attend to it today as best I can.

    The main thing that sucks is its all in the handlebars, the seat is quite comfortable still
     
  10. Hajuu

    Hajuu Member

    Currently im thinking of taking the following steps:

    1. Add on some very thick foam handlebar grips, with some weatherproof but removable glue.

    2. Add thin rubber under the flat handlebar mount bracket and the seat post mount all the way along the inner tube (if it will fit!).

    3. True up the motor alignment, add another set of rubbers (2x) to the engine mounts and tighten all mounting bolts

    4. Give the clutch and chain a really good greasing/oiling.

    5. Mix some fresh fuel with a racing 2 stroke oil (currently inadvertently using a lawn mower 2stroke). (Will this/Could this have an effect on vibrations?)

    6. Grease and repack wheel bearings, retighten, check tyre rim for buckles and attempt to fix as possible, check tyre is not out of round.

    Any other happy time generating vibe tips appreciated!
     
    Last edited: Apr 7, 2010
  11. sunsetboy

    sunsetboy Member

    rubber isolaters

    Check the rubber under your motor mounts. Mine require replacing every 6 months and you might want to consider upgrading your spokes to 12 gauge instead of the usual 14g. It will help keep your wheel true and round.
     
  12. Al.Fisherman

    Al.Fisherman Active Member

    Check out the rear sprocker for trueness.
     
    Last edited: Apr 8, 2010
  13. Hajuu

    Hajuu Member

    Ofcourse it wont fix the cause, the cause is its an oversized bicycle frame with a motor attached running at max speed (wide open throttle, not gaining speed). The ride upto this degree of speed is very smooth

    How smooth is your ride in this condition, maybe i'm wrong in my assertion.
     
  14. Al.Fisherman

    Al.Fisherman Active Member

    Both my ride (cruiser) and my sons ride (mountain bike) have no vibration issues at any speed (other then the standard that most engines have). I do not have rubber between the engine and tubes. I did have a problem on my first bike (frame split in 2 due to drilling a hole in frame)...my fingers felt they were still vibrating long after I got off the bike (in this case it was the bike as same motor installed on my current bike). The cause of vibration needs to be found not masked up. Now you can find out if it is the bike itself or the motor causing the problem. Have someone tow you on your bike with the engine off and clutch disengaged.
     
    Last edited: Apr 8, 2010
  15. Hajuu

    Hajuu Member

    Haha, well, it seems as though over the course of a weeks daily commute to work, the reason I kept noticing increasing vibrations was because it has literally been vibrating itself apart!

    On my way to work the other morning, I had to stop 4 separate times from things literally just rattling off... Shocking mechanic work on my behalf I can only surmise.

    Spent nearly an entire day cleaning every part of the bike and engine, re-oiling/greasing, tightning the chain, adjusted the clutch, tuned the gears and brakes etc.. Now it's quite literally the best ride. I couldn't be more happy with it, besides possibly a few tweaks for winter (see my other thread).

    At this point id just really like to thank all of you on here for your continued patience and support, I literally could not have done it without you guys.

    I'll post some pictures when I get a chance!

    Cheers!
    Hajuu
     
  16. sunsetboy

    sunsetboy Member

    chain alignment

    Chain alignment is also very important for the chain must run true to achieve max results. With my Felt Hot Wheels cruiser, the chain is not aligned properly so I went out and picked up a billet aluminum set of motor mounts to offset the "Felt" factor,lol.
     

    Attached Files:

  17. MikeJ

    MikeJ Member

    Hi Ron, Hajuu, Everyone -

    Attached should be a photo (I am an amatuer at attaching photos) of a small turnbuckle that I used and found it to greatly decreased the vibrations of my engine.

    I am of the opinion that vibrations are a default function of these simple engines rocking forward and backward while running; they are not balanced and we all accept that more or less.

    Rubber insulations help isolate the engine vibration from the bicycle frame, so we think that the engine no longer vibrates. I maintain the engine still shakes as much as ever.

    My thought is that if I can stop the engine from rocking, there will be no vibrations being transmitted to the bicycle frame, and to our hands, senses, etc.

    I attached the turnbuckle to a fixed point on the bike frame that will not move. Centers of downtubes and seattubes move back and forth in unison with the engine vibration. My thought is the three fixed points of the engine mount triangle don't move.

    I took some 14 gauge steel wire and a small turnbuckle. I threaded the wire through some point on the engine (I chose a jackshaft frame) and pulled that point toward the bottom bracket. I really had other reasons for the turnbuckle, but greatly diminished vibrations was a side effect outcome.

    So now I am thinking: If I anchored the engine to "hard points" like the bottom bracket or to just under the seat at the tube weld, the engine can't rock forward and backward while running. In the future, I am going to extend my turnbuckle finding to pull various parts of the engine toward "hard points".

    One thought is to loop a wire around the cylinder and draw the cylinder a tenth of an inch or so up toward the point under the seat. Frame tubes will resist the drawing tension. If the cylinder can not move forward or backward, there will be no vibration to transmit to the frame tubes. Tension of the pulling effort cannot be too much; I don't want to pull the cylinder off the crankcase block.

    If my thoughts work, pulling the engine in various directions with baling wire will look like it should be banned. But why not? My bike has been one experimental fix after another, and most have worked so far.

    Comments?

    MikeJ
     

    Attached Files:

  18. Al.Fisherman

    Al.Fisherman Active Member

    Last edited: May 3, 2010
  19. AussieSteve

    AussieSteve Active Member

    I agree with Ron. Vibration shouldn't be a serious concern, if everything is set up right. I barely notice engine vibration. The only vibration that bugs me is caused by rough roads, high tyre pressures, poor front suspension and no rear suspension.
    I check all nuts and bolts regularly and have never had any loosen from vibration, despite using very little Loctite.
    If vibration is an issue, fix the cause, not the symptoms.
     
  20. Al.Fisherman

    Al.Fisherman Active Member

    Ahhhhhh yes vibration....I remember that. My first and only build that I had issues with, the mountain bike that the frame broke due most likely (see I don't want to take 100% of the blame which I'm due, I'm sure the hole didn't help tho) to me drilling a hole in the frame, had vibration so bad that my hands remained numb for a 1/2 hour after I got off the bike riding a 10 mile trip. I to thought it was the engine. I soon realized that when I changed frames (to a cruiser) and mounted the engine correctly (according to my thoughts in the link above) 90% of the vibration was gone. So in the next 4 builds I made the engine fit the frame and not the frame to the engine. Have not had a abnormal vibration since, and they are now a pleasure to ride.
     
    Last edited: May 3, 2010
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