noises when going fast ?

Discussion in 'Frame Mounted Engines' started by erikvilla, Jan 15, 2007.

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  1. erikvilla

    erikvilla Guest

    Hi I have a 80cc engine on a mountain bike. the engine works very good but when i am going top speed or close to top speed i hear a loud rattling sound coming from the engine.. when i first installed the engine i dont remember it making this noise. The motor seems to work just fine but i dont no what can be making this noise my other new 80cc engine on my cruiser bike doesnt make this noise at all. can any one help me out?

  2. when I hit what I think may be close to me top speed my engine starts to whine, then a quick rattle and then an even hum crescendo... I don't like the rattle it makes before it gets to the hum though...

    I am on about mile 250 and I still haven't taken my engine to the max...
  3. I think i had same problem about brake in period.
    I was worried about it but then it dissappeared by itself after few days.
  4. erikvilla

    erikvilla Guest

    Well the rattling is really loud and it rattles when i have the clutch disengaged and then i reve it up high.. also if i am going fast and i coast with out giving it gas i hear the noise. I didnt really follow the break in rules and im wondering if this is related to this ive only been riding it for about a week now.. do you think it may be something that will go away?
  5. srdavo

    srdavo Active Member

    Nov 4, 2006
    Likes Received:
    I'd make sure everything is tight. look the frame over too.
  6. erikvilla

    erikvilla Guest

    I have checked everythign for tightness.. the sound is coming from the engine because when i reve it up when i have the clutch disengaged ( pedal mode) i could hear it coming from there.
  7. erikvilla

    erikvilla Guest

    Today i took the engine apart and found my problem. the piston was slopy on the conection rod so i removed the piston from the rod and found that my connection rod bushing was broken, which was caushing the piston to move around the cylinder head sloply causing the noises.
    Does anyone know where can order a new connection rod bushing for a 80cc chinease engine? please help me out if you know of anywheres
    thanks Erik
  8. Guest

    Guest Guest

    Bushing on connecting rod instead of a nice bearing is reason why lubrication is SO critical in these engines.
  9. Proboscis

    Proboscis Guest

    clutch pin (up and down) more grease
  10. gone_fishin

    gone_fishin Guest

    ok, you've proven yourself to be quite knowledgeble on these engines, what permanent pre-mix ratio would you suggest?
  11. Guest

    Guest Guest

    I'm typically a fan of 50:1 in most two strokes but for these, I would run it 25:1.

    FYI, small two strokes used in radio control airplane models often have an oil percentage from 17% to 20% (and higher) for exact same reason. At 20% oil percentage, that is 25 oz of oil per gallon of RC fuel. Crazy, itsn't it. Now, car model engines typically run as low as 7% oil to 14% oil (depending on fuel brand) because they value performance over longevity of engine.
  12. erikvilla

    erikvilla Guest

    I am still breaking in the engine and ive been using 18:1 for my mixture which is about 7 oz of oil to the gallon . I purchased the new bushing from and im gonna re-asemble my engine hopfuly by next weekend, but i still have two 80cc bikes running now so i have something to play around while im waiting to fix this engine :)
  13. Guest

    Guest Guest

    7 oz per gallon is a nice round figure and no harm is done by using it. Pull plug every month and brush it off is all you need to do.

    If you use AMSOIL 100:1 you can probably go down to 4-5 oz per gallon. The reason 100:1 AMSOIL can be used at that ratio for an engine that calls for a 50:1 ratio is that this 2 stroke oil has very little volatile solvents as a base for the 2 stroke oil. Most 2 stroke oil are 50% solvent carrier base....AMSOIL 100:1 isnt.
  14. Guest

    Guest Guest

    Back to original question:

    If you can't find obvious problem such as loose sh*t on engine or a worn connecting rod it COULD be detonation caused by any of the following:
    1. Engine is too hot
    2. Too lean of a mixture setting
    3. Combination of above
    4. Carbon on plug or piston which is causing preignition

    If this is detonation (pinging) you need to resolve the problem because detonation is VERY damaging to an engine. A quick fix is to try higher octane fuel and see if you have the noise. If you do, it ain't detonation.
  15. JosephGarcia

    JosephGarcia Guest

    I have a pinging noise that I cannot identify. I hear it only at idle, no other time. I looked at my piston once through the exhaust port and it looked like it had some carbon on it. you say this is very damaging to an engine but It's been running fine for months.

    I also heard from someone else that a pinging noise was caused by a small metal shaving loose inside the crankcase.

    a friend of mine said it was the gears in the clutch section of the motor weren't greased enough, after they were regreased, the noise got alot better, but I still hear a small pinging,
  16. Kielohawk

    Kielohawk Guest

    This just happened to me. The upper bearing (bushing) on the arm just went out.

  17. Hugemoth

    Hugemoth Guest

    Let us know if you find a source for these bushings. I'd like to have a couple and the engine sellers don't seem to be able to get them. I'm sure I could make them out of a larger bushing from a bearing shop but it would be time consuming.


  18. OldPete

    OldPete Guest

    Accurately measure the piston pin diameter, the rod small end bore and note the width of the rod's small end. Then do a Google with those dimentions. I forget in which order most all catalogs have them but that will be easy to note.

    I would not use sintered bronze bushings that are impregnated with graphite or oil for some reason and I don't know why, except I have never seen them used in any con-rod.

    If I found bushings that would just thumb press into the rod, I would be tempted to use them with a red loc-tite install. The bore of the small end and the bushing would get a lite sanding, just to break the surface, before the install w/Mr. Red.

    A machine shop could ream the bushing real close to dimention.

    Cleaning out the crankcase is another issue. :cool:
  19. Kielohawk

    Kielohawk Guest

  20. OldPete

    OldPete Guest

    Buy it!

    Deburr the edge of the rod's small end hole, then draw the bushing in with a fine threaded bolt with stiff washers on both sides.
    First make sure the rod's small end itself was not damaged. Start the bushing very straight, it may take a few attempts with only light pressure from the fine threaded bolt.