Any way we can dampen the engine?

Discussion in '2-Stroke Engines' started by retromike3, Jan 26, 2010.

  1. retromike3

    retromike3 Member

    I road my motorbicycle about thirty miles today and half way to my destination my carburetor top rattled off and I lost power right away. Well I got it going again but it seems like every part on that bike will rattle off unless it has ether lock tight or two blots or welded in place. There has to be a way you can mount the engine so that it won't transfer all of that "buzzing" to the frame and rider.:detective:

    Any Ideas?

    mike Frye the bike guy

  2. Fabian

    Fabian Well-Known Member

    retromike3, be thankful your engine is rattling, just loctite every nut and bolt in place - when vibration becomes almost bearable, you're soon to be left with one option - pedal power.

    Also, be thankful your engine is spewing out copious quantities of 2-stroke oil that coalesces into black filth and grime - when your engine starts running clean, pedal power is close at hand.

    Last edited: Jan 26, 2010
  3. Dilly Bar Rob

    Dilly Bar Rob Member

    I had LOTS of vibration on my folder bike - my bottom would actually start to tingle quite bad after a km or so at higher speeds, even with having a cloud9 sprung/gel seat.

    I upgraded to a 40 tooth rear sprocket from the 44 a few weeks ago to get a bit more speed (the bike has 20" wheels so with the 44 it was quite slow). Not wanting to deal with the rag joint BS again (and wanting to take the stress off the spokes) I had a buddy WELD the new sprocket directly to the rear hub (too cheap to get a clamshell adapter...). We managed to get it dead center which was impossible with the rag joint (spokes never lined up properly because of the hole/spoke count) and BAM, all the bad vibes are gone! Seems that the vibration was due to the chain getting tight/loose (even just slightly) as the rear sprocket turned. The bike also rolls a lot easier/quieter now with the clutch in/engine off. After this I am starting to think that the rear sprocket being off center may be one of the main causes of vibrations (while riding) on HT setups. I am definitely welding the rear sprocket on again on my next build.

    I get very little vibration from the engine itself and it is mounted to the frame SOLID (front mount welded to frame). I recall that I did get a bit more vibration when the engine (zoombicycles pk 80) was new, but that got a lot better after break in (maybe 200km).

    Some people put rubber between the mounts and the tubes, however I suspect this just protects the bikes paint more then anything - I wouldn't expect a thin, highly compressed piece of rubber to dampen much of anything, you need rubber blocks to do that effectively. I personally don't like that idea - I think that rubber between the frame/engine would just make it easier for the engine to "turn" outwards when under load. I like when stuff is solid.

    I have seen some nice aluminum/rubber block mounts for the HT that look like they would do a good job absorbing engine vibes, possibly on the motorized ridley twin bike that was discussed in a recent thread here on the forum (not 100% sure on that). I think somebody actually found the "source" of the mounts (in an older thread about the same bike), but they were expensive, over $100 if I recall.

    I also remember reading about somebody filling the frame tubes with expanding foam to reduce vibrations, maybe look that up.

    Hope this helps, Dilly Bar Rob
  4. CaptJ

    CaptJ Member

    Hey Dilly Bar Rob,
    Like Fibian said loctite every nut and bolt in place. Do a inspection often. I don't have much vibration on my bike I barley feel it. The vibration comes with speed changes on mine. The motor mounts should installted with rubber on the frame.

    My front mount is made of Oak the back mount is wrapped in
    rubber, too much vibration than I can feel.

    Good Luck On Yours,

    ... Jim

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  5. Dilly Bar Rob

    Dilly Bar Rob Member

    Ha! Wasn't even looking for it and found it!

    Here is a link to those fancy motor mounts. They say they are for felt cruisers but I imagine they could be made to work on different bikes as well.

    Looks like I was wrong regarding the price - $199.99!
  6. CaptJ

    CaptJ Member

    IMO: Thats too much! My oak motor mount cost $2.00 from Home Depot. That mount for $199.00 is a beautiful thing if your building
    a custom bike.
    Last edited: Jan 27, 2010
  7. I used rubber handlebar grips under my engine mounts and have 0 vibration even at 30mph.
    And i have 1,000miles on my engine.
  8. give me vtec

    give me vtec Active Member

    that is an excellent idea... i love the ingenuity on this site. Its endless... hundreds of solutions for any given problem.
  9. Old Bob

    Old Bob Member

    Garden hose... pail of water maybe...:whistling:
  10. Stan4d

    Stan4d New Member

    And I was going to use them as grips for a dog stick. (something to whack chasers who got to close) I figured with the soft grip it would only stun them.
  11. GearNut

    GearNut Active Member

    Hocky pucks seem to make excellent mounts too, or so I have read. I have not made one yet.....yet.
  12. AussieSteve

    AussieSteve Active Member

    Why hockey pucks, in particular? Never heard that one before. Where did you read it?

    ... Steve
  13. BAM

    BAM Member

    i used an old inner tube around frame mounts works good ive heard hockey pucks used for a cheap body lift on trucks before drill a hole and stack them together also heard that leather belt will work
  14. Dilly Bar Rob

    Dilly Bar Rob Member

    Lol, I have actually seen wood used for that purpose also :rolleyes7:
  15. MikeJ

    MikeJ Member

    The oak (or other hardwood) engine mount is a great idea! I will have to try that on my own bike.

    The hockey puck idea does have a rational explanation. Assume all your engine mounting bolts are tight; they won't allow the engine to move against the frame tubes. What is overlooked is that the frame tubes themselves flex back and forth at the speed of the engine RPM. At a point called resonance, the vibrations from engine to frame tubes to the rider is especially bad. On my bike, that happens at around 4600 RPM according to my SenDEC tachometer.

    What to do? Keep the frame tubes from vibrating. How? Make the tubes thicker (not really an option). I could wrap a heavy weight around the tubes to shift the resonant point to a much lower frequency. Hence, attaching weights such as hockey pucks to the tubes. If I could find thick strips or long rods of the metal known as lead, I would wrap the lead around the three tubes that make up the engine mounting frame.

    In my case, I am able to cruise comfortably at 4200 RPM and avoid annoying vibrations until some mounting bolts vibrate loose. Then it is time to again check every bolt holding that engine to frame and tighten them all down again (until next time).

    I hope this helps.
    960 miles and waiting for warmer weather
  16. CaptJ

    CaptJ Member

    The oak is easy make and its very solid. I also think it takes a lot vibration out.
    Whats your SenDEC tachometer?

    ... Jim
  17. MikeJ

    MikeJ Member

    The SenDEC tach is just a little digital tach. Some readers use another digital tach called Tiny Tach. Just do a search on SenDEC. The model I have displays RPM and hours of running time. It is not a fancy unit. Look for surface mount models and you will see what I mean.

  18. CaptJ

    CaptJ Member

    Thank you Mike for the info.
    ... Jim
  19. V 35

    V 35 Member

    I put a piece of fuel line in a rubber chair tip, and stuffed that in the half hole where the front mount casting is. When the bolts tightened, rubber compressed a bit, dampens vibration, still bolts down pretty solid [ time will tell ]