Too much vibration.

Discussion in '2-Stroke Engines' started by Eddiesilverbullet, May 24, 2016.

  1. Eddiesilverbullet

    Eddiesilverbullet New Member

    I have a problem with my 2 stroke engine. I just installed a decent expansion chamber but it still vibrates like crazy causing nuts and bolts to come off. What can I do? And does anyone know of a repair shop in the orange county area? Please help
    Thanks.
     

  2. jaguar

    jaguar Well-Known Member

    ha! that's normal for this engine. It drove me crazy till I investigated the subject, did some calculations, and then drilled two holes into the crank wheels to balance it correctly.
     
  3. crassius

    crassius Well-Known Member

    first, if it is a pre-2012 motor (ebay sellers still have those for the cheap kits), then it does not have the balanced crank - these are the old bone-shaker motors we all had to deal with years ago

    if it is a newer motor, then vibration can be caused by rubber motor mounts (real bad idea) or by a cracked frame

    sometimes just moving the motor lower can help frame absorb vibration better
     
    Eddiesilverbullet likes this.
  4. jaguar

    jaguar Well-Known Member

    even the new ones vibrate too much
     
  5. FurryOnTheInside

    FurryOnTheInside Active Member

    I think you make it sound too simple! Removing the primary cog, splitting the case halves, removing the crank, drilling big holes in it, packing them with foam and JB Weld to keep the CC pressure, reassembling crank and case without knocking it out of true.... I read the (your) article and had a good think about it, and decided I will just get the piston holed and wrist pin opened out (when I find someone who has a drill press I can use), and fit a retarded CDI. :)
     
  6. 45u

    45u Active Member

    Buy a bottle of thread lock or other brand and a bunch of nylock nuts!
     
    Timbone likes this.
  7. FurryOnTheInside

    FurryOnTheInside Active Member

    Loctite 242? And 263 for the studs?
     
  8. 45u

    45u Active Member

    If you are going to use in a high heat area makes sure you use a thread lock is hight heat. All the common thread locks you use heat to brake them lose. Read the card it comes on.
     
  9. jaguar

    jaguar Well-Known Member

    loctite won't reduce your annoyance from the vibration.
    I've taken motorcycle cranks out so this engine felt like I was a kid playing with a toy. nothing hard about it to me.
    don't have to worry about filling the holes with JBweld because crankcase pressure is not critical for a low reving engine.
     
  10. jaguar

    jaguar Well-Known Member

    How many of you all would rather suffer vibration (and nuts flying off) for hundreds of hours instead of working a couple hours to make the crank right?

    ps- lightening the wrist pin is not enough
     
  11. FurryOnTheInside

    FurryOnTheInside Active Member

    A couple of hours? Hmm *looks sceptical* -_- okay I am in no rush while I'm saving up for shift kit bits so I am considering reconsidering splitting the case.
    I am worried about getting it back together again without making it worse, though. I think most people who have read earlier posts about it would be too.

    I have read that much of the vibration problem is solved by reducing the pin and piston weight (easy if you can get access to a drill press), and correctly timing the ignition after the engine is built and running. (But how much this helps seems to be difficult to quantify)

    What tools are required to make the modification to the crank and to reassemble it correctly?
     
  12. 45u

    45u Active Member

    And how many people have the knowledge or the know how to balance the crank? Some more then likely would only make things worse or mess up something. I know some folks when they change a spark pug I get nervous. This is why many make s living working on them for those that do not know. But thread lock and nylock nuts will help keep things from falling off and most can do this. Yes it dose not stop the vibration but at least you can ride without have to stop so much or at all.
     
  13. crassius

    crassius Well-Known Member

    seems easier to assure the crank is balanced before ordering that motor
     
  14. jaguar

    jaguar Well-Known Member

    the lighter the piston assembly (including the pin) is, the closer you can get the balance to perfection.
    I'm just about finished with my balance calculator and can tell exactly what size holes to drill. I've got someone who is willing to do the work as a test case (69cc) so others can follow his example. I successfully balanced my 55cc (upgraded from 48cc) but it had non-stock piston and wrist pin. It needed two 9mm holes but that size requirement may be different for a stock engine.
    tools that are sometimes helpful: rubber mallet, impact driver

    Does anyone know of a video showing how to split the cases and remove the crank?
     
  15. 45u

    45u Active Member

    You can if you order from a place that sells motors and balance cranks for another $100 to $150 that will make the price of the kit go up that much or more so the kit will cost you $250 to $300 maybe more. None of these cranks are balanced well some are worse then others. Now why you are balancing the crank do not drop it or hit it put too much presser on it when drilling holes you you can get the crank out of true and a balanced crank out of true is just as bad sometime worse than a out of balanced crank. So want do it your self make sure you know what you are doing!!!!!!!!!! If not dig in to the pocket and shell out MORE money as it might be cheaper.
     
    Last edited: May 25, 2016
  16. 45u

    45u Active Member


    Jaguar looking forward to the experiment and seeing how it works. Will have my eye out here and on your site.
    Thanks so much for your input and time.
     
  17. jaguar

    jaguar Well-Known Member

    I think it was Fabian that ordered a “balanced crank” (or engine with balanced crank) and he sent it back because it vibrated so much. If you want something done right you have to do it yourself. The internet has been void of what I’m fixing to offer for free- a crank balancing program. No wonder dealers fail to properly balance a crank when all they have to go on is the old wives tales of how to.
     
  18. 45u

    45u Active Member


    This is why YEARS ago I started doing my own work as I trust my work but not others. This was way back when I was 15.

    Jaguar do you know who the company was? I called and talked to a shop about balancing cranks and from the way they talked I sure would not let them put a spark plug in my motor if it was frozen up and they are suppose to be a big race motor builder.
     
    Last edited: May 25, 2016
  19. Timbone

    Timbone Active Member

    My hypothesis is that any kind of vibration problem relates directly to the bicycle frame. Bicycle frames work best the stiffer they are. That's the idea: a stiff frame transmits the pedaling force as efficiently as possible to the wheels. Frame flex is a no no for a racing bike. You strap a motor in there (a one cylinder engine at that!) and vibrations have to get worked out somewhere.

    Once I was descending a big hill with a bike racer buddy and I watched as he experienced a speed wobble at about 50mph. He very quickly lost control and slammed directly into a cliff face. Yes, every rigid bicycle frame has a natural vibration resonance point.

    I would think that creating a frame with flexibility could be a way to seriously relieve vibrations. Instead of all tubing connected via unyielding welds, maybe a key joint held by something strong but flexible (like steel cabling) could work as a kind of shock absorber while not affecting safety or performance.

    A rear swingarm linking the rear wheel to the frame via shock absorbers would help, too.
     
  20. jaguar

    jaguar Well-Known Member

    It's easier to drill two holes in the crank than to reinvent the frame.

    I just finished the program and figured that for a Grubee with near stock compression and a weight of 95 grams for piston and pin and bearing that two 3/8" holes would be perfect at 5000 RPM and would be at the limit of the yummy zone at 6500 RPM. If the piston assembly is only around 85 grams then those same holes would keep the engine balanced up to 10,000 RPM. I'm not sure what the stock piston weighs. These figures are for the cranks with four 15mm diameter holes. If you take yours apart and it is different then let me know the specs and I'll run the program for you. Best drill bits are carbide. Home Depot has them for around $6.
     
    FurryOnTheInside likes this.
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