Motor Sliding Down Seat Tube And Down Tube

Discussion in '2-Stroke Engines' started by groove9028, Sep 7, 2010.

  1. groove9028

    groove9028 New Member

    I've mounted the motor as flush as i can with little to no gap with the mounting hardware. I put electric tape below each of the mounts to make it a tight fit. all the bolts have been tightened down as tight as i can, and yet it still moves. any recommendations or suggestions to fix this problem would be greatly appreciated! will post pics soon.


  2. GearNut

    GearNut Active Member

    It sounds as though the frame tubes are too small?
  3. skrufryder

    skrufryder Member

    you could get those universal drill mounts
    or weld some steel plate as mounts
  4. HeadSmess

    HeadSmess Well-Known Member

    :eek: is such a thing actually possible? usually the exact opposite... :ack2:
  5. GearNut

    GearNut Active Member

    Yes it is. I have a Murray cruiser from the 80's in my backyard. The frame tubes are too small for the motor mounts, and my motor has the small mounts, not the newer larger mounts.

    I strongly recommend staying away from any motor mount that requires you to drill holes in your frame. Research Al.Fisherman's posts. He has photos of how his frame cracked through right where he drilled his. He is not the only one that has had this problem with the drilled frame mounts either. Drilling a hole in your frame is inviting disaster if the frame were to crack while you are at speed.

    For tubes that are too small, try to work out a spacer or shim arrangement to fill in the gap. Right now I am thinking PVC sprinkler pipe, but I do not know if that would be strong enough or possibly crush/ wear down over time with all the vibration that these engines create. Perhaps if it were routinely inspected and new pieces installed when necessary?
  6. pbeggs

    pbeggs Member

    try a couple of layers of innertube glued around the frame where you are mounting the motor (also cuts the vibration way down)
  7. GearNut

    GearNut Active Member

    More often than not, rubber mounting the engine mounts results in broken mounting studs.
  8. RedBaronX

    RedBaronX Member

    How so? with how much my bike is vibrating, I was going to add the rubber pads, but not if it's going to break stuff in the long run...
  9. GearNut

    GearNut Active Member

    With solid mounts the vibration is transferred to the entire bicycle frame and it absorbs it as a whole unit. Also the engine is solidly mounted and the relationship between the mounts and frame does not move.

    When rubber is placed between the mounts and frame the vibration is mostly contained to the engine alone. The whole bicycle cannot absorb it. The engine mounting is flexible and the mounts can move on the frame. This movement stresses the mounting studs and the stress can lead to broken studs or worse, a broken engine case around the stud holes.
    There are plenty of threads and posts on this site to support this information.
    What I am trying to do here is pass on the hard lessons learned from others on this site to you.
  10. Al.Fisherman

    Al.Fisherman Active Member

    1. If the engine can slide down the seat tube, I'll guarantee that the engine is not mounted correctly. If it were it would be IMPOSSIBLE to slide down. The front mount wouldn't allow for this to happen.
    2. It is possible that the engine mount is too large for the tube. I have two different engine mounts, one fits perfectly, the other is too large. With one not large enough it is easy to fix. The clamping service can be enlarged by sanding. You can use a piece op pipe or PVC the same size as the tube, wrap with sandpaper, and sand till you have a proper fit.
    3. A mount that is too large for the tube can be shimmed out, dang I hate to do this, but you can get a copper or brass pipe coupling, cut in half (from end to end), and fit as snug as you can.
    4. Use proper torque.. 50 to 70 INCH pounds (NOT AS TIGHT AS YOU CAN). I find that in order to torque the nuts properly, the engine mount clamp gets in the way of the socket. To correct this I install a shim (about 1/2"long) between the clamp and nuts.

    AS far as what Gear Nut mentioned above, believe it. Proof in pictures if you want.

    Proper mount fit. Notice the shims.
    Notice the space between the mount and clamp at the studs?

    Drill baby drill....

    You can see that the mount on the left is too large for the tube. Also pictured is a engine mount shim. Easy to bend, form fit and cut to fit the engine mount.
    Last edited: Sep 10, 2010
  11. Hajuu

    Hajuu Member

    Just for my two cents, I have also had problems with using rubber to mount the motor. One would imagine it would dampen the vibrations, but when you think about it logically, the vibrations are all going to end up in the frame, one way or another, and also once again logically, the vibrations are only going to pass through roughly the same area into the frame, with or without rubber. There is possibly like a 1% reduction in frame wear.

    Also as stated, i've experienced problems with bolts stripping due to them being.... excessively cheap and nasty, and also have noticed a tendancy for non-locktite'd bolts to undo themselves over time causing issues if you don't check them regularly (which you should anyway).

    There are many, many alternate mounting solutions if the packaged brackets do not fit your frame, however unless your frame is very new and made of composite materials, it seems to me that it may be too thin to really provide the engine with the support it requires.
  12. RedBaronX

    RedBaronX Member

    trust me, I would never question the validity of your advice, I just wanted to know the science behind WHY pads would stress the mount screws. And I knew you would deliver :)
  13. HseLoMein

    HseLoMein Member

    I used a lead pipe as my engine shim for the front mount to see how it would perform. All i can say is wow. I will be soon removing the engine to all the shims to all the mount points. Lead is awesome, almost removed all the vibration, from the engine.
  14. GearNut

    GearNut Active Member

    Watch it carefully. Lead deforms easily and you may soon have loose fitting mounts.
    I am not saying in a week or two, but a few months down the road.
    Just be careful using it as a spacer material.
  15. HseLoMein

    HseLoMein Member

    Very True, i will keep a close eye on them.