Gravity or siphon gas line

Discussion in 'Motorized Bicycle General Discussion' started by scribling, Feb 12, 2015.

  1. 2door

    2door Moderator
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    Copper is not a resilient material.
    I'm talking about rubber, silicone, foam, etc. All of those things people have tried to 'eliminate vibration'.

    This has been posted here numerous times by me and others. You can not eliminate the vibrations produced by a single cylinder, 2 stroke engine. Trying to put rubber between the frame and engine only transfers the vibrations, and amplifies them, to the engine mounts and fasteners. Fastener failure is almost assured as well as in increase in the vibes felt in the bike and attached parts such as fuel tanks, fenders, handlebars, etc.

    There is always the argument that motorcycles and cars use rubber mounts. That's like comparing apples to oranges. The mounting system is all together different. Simply sticking rubber between a Chines 2 stroke engine and the frame WILL NOT eliminate vibration.

    Tom
     
  2. Flyman

    Flyman New Member

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    Tom I agree 100 percent with that mounting solid. But to this day I never
    understood why. Can you are someone shed some light on this for me.

    Fly
     
  3. 2door

    2door Moderator
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    Fly,
    Let me see if I can put this simply.
    When you place rubber, or a resilient material between the engine and the frame the engine will then be allowed to move within the constraints of the rubber. That movement is then amplified and transfered to the mount fasteners, which are usually the first to fail. Another way to say it is the more the engine can move the higher the vibration.

    Not only is this increased vibration then felt more in the frame but the stresses are more than the mounting system, as designed, can take.

    Motorcycles and cars use a rubber, resilient mount but it is in effect a sandwich of metal, rubber, metal. This system will act as an absorbent to isolate engine vibration, movement, between the engine and the vehicle frame. There is no metal to metal contact.

    When one just puts rubber between the mounts and the frame, without that sandwich concept, the engine is allowed to move more that it could and the vibrations are increased because of the movement. Every vibration cycle is then transfered directly to the metal parts of the mount, fasteners and frame and is felt by the rider and parts attached to the frame.

    Mounting the engine solid to the bike frame doesn't allow the engine to move. Therefore the vibrations are limited, and distributed evenly throughout the frame. This reduces what you feel in the frame and handlebars and its effects on other parts.

    If you have the opportunity, closely examine an engine mount used on a motorcycle or an automotive application and you'll easily see the 'sandwich' concept I described above.

    Also keep in mind that most motorcycles and cars do not rely on a single cylinder 2 stroke engine for power. Those that do either used the solid mounting concept or a resilient, sandwich, style of engine mount.

    I hope my meager attempt at an explanation helps.

    Tom
     
    #23 2door, Feb 14, 2015
    Last edited: Feb 14, 2015
  4. KCvale

    KCvale Active Member

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    I couldn't agree more.

    Get the back mount at a 90 to the seat post and tie in the front to match, all metal to metal with as close to a 360 grip on the bike bars as possible.

    Sure there are crap engines that are way out of balance, but most aren't.
     
  5. Flyman

    Flyman New Member

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    Well that's what I did on this first build & have not had a problem. I do listen to you
    guys, for you been there done that. But that's one I did with out understanding.
    Very good read Tom, I thank you for clearing that up for me

    Fly.
     
  6. 2door

    2door Moderator
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    I just thought of a way to illustrate solid, as opposed to resilient mounting.

    If you have access to any type of vibrating appliance, say like a hand held engraver. Hold it lightly between your fingers or in your hand and turn it on. Feel the vibrations and in some cases you can even see the appliance, or tool move, or vibrate.

    Now clamp your hand around that tool tightly, Hold it and you'll hear and feel the vibrations being reduced. This is because you are keeping the tool from moving in your hand as much as it did when it was being held lightly. This is similar in concept to clamping an engine tightly against the frame.

    In other words, the more the source of the vibration is allowed to move the longer, or larger the frequency of vibration is allowed to become. If it can't move, the vibes are held to the absolute minimum. If it can move, in the case of rubber mounting, the vibrations increase.

    Tom
     
  7. scribling

    scribling New Member

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    Really? I think the first time I mounted it I had crazy vibration which is why I tried the rubber dampeners. It's been a while now so I can't really remember. I think it's just a piece of inner-tubing. I'll have to take a look. If so, I'll try it metal to metal and see if that makes any difference. I would love to get rid of this outrageous vibration.
     
  8. 2door

    2door Moderator
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    Scribling,
    All of the explanations offered regardijg vibrations can't take away the fact that some engines are inherently 'out of balance'. In other words they were not built as well as some others.

    You've probably seen here the words, "they're a crap shoot'. That simply means that due to the quality control employed by the manufactures that some engines are simply better than others. Most builders who have experience with a lot of engines will tell you that "some are great, some are dogs".

    It could be that you have an engine with a noticible 'out of balance' crankshaft and in that case there will be little you can do about it.
    Nevertheless, try mounting it as solid as you can and tell us what your results are.

    Tom
     
  9. scribling

    scribling New Member

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    I'll give it a try tomorrow and report back.
     
  10. mapbike

    mapbike Active Member

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    Ditto....100%

    Been there done that, rubber or anything soft between engine and frame is a big mistake and will cause the mounting hardware to fail.
     
  11. maniac57

    maniac57 Old, Fat, and still faster than you

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    Tom has it right here.
    A bicycle engine that is rubber mounted moves a LOT more than a solid mount.
    Bolting the engine down solid to the frame allows the frame to dampen the vibrations where rubber simply attempts to control the movement in the rubber, which quickly destroys mount bolts and strips case studs.
    This is also the reason I dislike aluminum frames, since they do not damp vibrations as well as steel unless they are of very high quality. They can also work harden and crack from the constant pounding.
    A good fitting mount saddle with no gaps and nice tight mount straps is a much better way to reduce vibration than rubber.
    Large frames like my Specialized HardRock dampen vibes even more since the bigger frame spreads the load better.
    The paint under my mounts is still intact after five or six different motors.
    Notice how you never see me posting about stuff falling off or breaking?
    Solid is the only way to go unless you have mad machining skills and a degree.
     
  12. Flyman

    Flyman New Member

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    Aluminum frames work hardening! That's something I would have never thought about.
    This stuff needs to be made into a sticky. The average Joe lunch bucket guy coming
    into this hobby would never know this stuff.

    The only reason I mounted my engine solid was I read my tail off.Most people would
    think to mount in rubber be cause there cars motor mount & so on. It would save a lot
    of trouble with all the problems listed above.

    Just my thoughts, & thanks for explaining this.
    Fly
     
  13. boxcar

    boxcar New Member

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    Actually Tom , the copper tubing is to prevent the studs from being pulled out of the sheet metal tank.
    The dampening system I refer'd to is at the motor mounts.
    I use Gorilla tape as a dampener. Several layers. It does not have the compression issues soft rubber has, and can be tailor'd to the frame diameter.
    I agree that slapping a layer of soft rubber between the mounts and the frame is a bad idea. To soft....
    But a buffer is needed. And will reduce vibration.
    As well as a well balanced engine / good quality fasteners and care when assembling the bike.

    [​IMG]

    [​IMG]

    I have been in the motorcycle building business for 35 years.
    While cars rely on multi cylinder engines as do larger bikes . The venerable single cylinder 2 stroke was the norm for not only nearly all dirt bikes but also most small road bikes for better than half of motorcycle history.
    It only fell out of favor due to emissions.
    All were rubber mounted .
    All used the cradle mounting system , using lateral bolts ( at right angle to the motor).

    I'm not fond of the sandwich description.
    What you are describing is a " vulcanized motor mount" used in cars.
    It's a way to bond the rubber to the mounting plate. This allows the mount to function without the need for a through bolt.
    Motorcycles don't use that style mount.
    They use a tube and bolt method where the rubber is in the tube with a steel sleeve through the center encasing the through bolt. More like a shock absorber mount.

    The problem we are suffering from is caused by clamping the engines to the frame.
    A necessary evil when one is trying to design an engine to fit so many different applications.
    Transferring the vibration to the frame is a bad idea .
    This will cause stress cracks . It's an engineering inevitability.

    Finding the right material to use as a dampener is a far better idea.
     
    #33 boxcar, Feb 15, 2015
    Last edited: Feb 15, 2015
  14. 2door

    2door Moderator
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    As I and others have said many many times here; you have to do what works FOR YOU!

    The old rubber mounting issue has been with us from the beginning and will probably never go away. Those against it base their opinions on the experience they have had with trying it themselves or seeing the results of attempts to successfully rubber mount and engine.

    Boxcar's method works for him and that is great. I will say that the thickness of his chosen material is key to his success. The thinner the resilient layer is the more likely you'll have success. The thicker, softer it is the more you're going to see negative results.

    One point I want to touch on is Boxcar's description of the motorcycle mount. This style, as I said above, does not require a metal to metal attachment. The through bolt he mentions is free to move within the flex of the rubber bushings. Therefore it is in effect a 'sandwich' or metal, rubber, metal, rubber. It is not attached solid to the frame like the Chinese 2 stroke engine kit mounts dictate. There's a big difference.

    Tom
     
  15. boxcar

    boxcar New Member

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    Yes and no. The steel bushing running through the rubber on a motorcycle mount is slightly longer than the rubber. The through bolt locks tight to this bushing and essentially
    Floats in the rubber sleeve.
    Neither here nor there.
    The fact remains that a dampener of sorts is needed.
    Thin or semi ridged is best.
    On a mountain bike build where the China Girl mounts don't fit the frame geometry.
    I machine UHMW mounts that replace the rear block and are tailored to the front down tube.
    Metal on metal is what I avoid.
    But the engine must be solidly mounted.
     
  16. fatdaddy

    fatdaddy New Member

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    I've said it a hundred times and I'll say it again.
    IT'S YOUR BIKE, BUILD IT YOUR WAY.
    I've seen a few frames crack at the mounts, Mostly Aluminum frames or from badly mounted engines. I still think metal to metal is best, BUT, if you dont get both mounts flat, flat, flat, on the frame, yer gonna wind up with a corner or edge digging into the frame and it will break. This happens more easily on aluminum than steel. THEN, Theres the dredded "LARGE FRAME KIT" that sometimes comes with the engine kit. Drilling a hole in yer frame and running a bolt through it is probably the worst thing ever recommened by the engine makers. That'll crack a frame almost every time. SO YUP, I vote metal to metal. Also, theres some guys making some very nice after market mounts. Most are beyond my bank account capacity but When I win the lotto I'll try them.
    IT'S YOUR BIKE, BUILD IT YOUR WAY.
    fatdaddy.usflg
     
  17. boxcar

    boxcar New Member

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    You are correct. It is your machine build it any way you want.
    But don't ride it on public roads where others may be affected by a possible failure do to cost savings deem'd appropriate by the builder.... The public road thing makes it everybody's business.

    I have seen more than a few stress failure's in my day. Most are caused by harmonic distortion. (vibration )
    Alignment is very important as you state. But it doesn't solve the harmonic problem .
    A builder recently posted pics of a Hawk frame that broke due to vibration. It was solid mounted.

    I'm not here to beat you up but you stated that:

    Wile I agree that soft rubber raped around the frame is a bad idea. I disagree and wouldn't advise any new builder to solid mount a motor in any machine for the reasons I have stated.
    And yes I am an experienced builder.......
     
    #37 boxcar, Feb 15, 2015
    Last edited: Feb 15, 2015
  18. Davezilla

    Davezilla New Member

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    I couldn't have said it better myself...
     
  19. maniac57

    maniac57 Old, Fat, and still faster than you

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    I agree. All free advice is worth exactly what it costs.
    Pick and choose what works for YOU.
     
  20. Trey

    Trey $50 Cruiser

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    fatdaddy- Did you see my post on the fact that it took me TEN hours to mount a 4 banger on a 29" Onex? No joke. Lack of experience, or lack of skill, I don't know ;)
    ...but without having machined mounts, if you put the time in, you can still get it hella flat to the frame. That's the right way.

    Metal to metal.
    I believe.

    IT'S YOUR BIKE, BUILD IT YOUR WAY.
    Words that have motivated me plenty of times.
     

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