Engine Mounting Bolts Destroyed

Discussion in '2-Stroke Engines' started by kmon, Sep 15, 2015.

  1. kmon

    kmon New Member

    Three out of four of my engine mounting bolts have been cut clean off from just riding.. I have no idea why! I have a skyhawk frame gt2a with a silver slant 66cc. The bolts are now flush with the engine and impossible to get out. The only fix I can think of is drilling out the spots and trying to drive new bolts in. Please help with any suggestions. I can take pictures. Thanks

  2. butre

    butre Well-Known Member

    are you using rubber between the engine and frame? if so, stop. that's what breaks those studs.

    as for getting those studs out, go at the area with a cutoff wheel on a dremel and then back it out with a flathead screwdriver
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  3. KCvale

    KCvale Motorized Bicycle Vendor

    ...Or get an easy-out and corresponding drill bit and drill little pilot holes into each broken bolt and back them out that way unless you put them in with locktite, if that's the case you'll need to put the engine in a drill press, drill them out, and then re-tap bigger threads.

    That is really messy and hard to do.
    The soft engine case will give quicker than the bolts themselves so it can get messy real quick trying to do it freehand.

    Using a grinder or dremel you can X the bolt for a center mark to hold the drill bit in the center.
    Ya, it will cut the case some but that's OK, there is enough material there.

    When you do get them out and re-mount the engine do 'The Test'.
    A well mounted engine won't just shear all the studs, it HAD to be way loose and rode anyway to do that.
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  4. crassius

    crassius Well-Known Member

    if drilling and/or extracting by one or the other method won't work, search for "80cc alternate engine mount" and you'll see some ways to bolt a piece of angle iron to the case to hold it well
    Luybaton likes this.
  5. kmon

    kmon New Member

    Thanks so much guys, the dremel and cutoff wheel worked great. I haven't been using rubber or anything, I think the problem was with looseness. Thanks again for all your ideas!
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  6. crassius

    crassius Well-Known Member

    when you remount, remember that the goal is not to make the mounting bolts tight, but to make the motor tight - this means adding whatever amount of spacers that may be needed to get the motor to fit snugly in the frame before the bolts are ever tightened
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  7. Tauseef

    Tauseef Member

    Hey , i was planning to add rubber(cut piece of car tyre TUBE ) as shock absorber at the engine mounts with cycle frame.
    SO i shouldnt do that ??
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  8. skyash

    skyash Active Member

    I have tried rubber be for and it let's the motor move under load my friends bike worked for a long time like that but in the end it came to lose all the time and had to hold the motor on with his foot to ride it I think it's better to be solid on the bike.
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  9. butre

    butre Well-Known Member

    definitely not. rubber in the mounts is the single biggest cause of failure
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  10. Learner4life

    Learner4life New Member

    I cant agree more here!!! This is SO important. I am a noob that learned the hard way. The comment also before about the engine case being soft is so true also.

    What I do now when its engine mount time is this:

    - First, make sure bike frame is secure, upright and level/close to final riding position etc(meaning if the wheels arent on it, just make sure the frame is not rotated way forward or back etc if that makes sense), best to have the front and rear wheels on bike and tight, I dont worry about getting the chain over the rear sprocket etc until after the engine is mounted perfect.

    -Now find the sweet spot for the engine. Without any rubber or anything at all between the frame and engine (metal to metal) I lower it into the "V" trying my best to keep the frame tubes as perpendicular and flush as possible on either side. I want to gently shimmy it back and forth into place, NOT force it(this can cause frame stretch which is very, very bad!) Tap the engine a little on each side, rotate it, etc. try a few different angles and take your time. Every engine/frame combo "should" have a sweet spot, or at least a best position possible.

    - After I have the engine perfectly wedged between the two frame tubes, making sure im fitting flush on both sides, hopefully have 0 or as little gaps as possible between frame and engine mounts. Its ok to have small gaps though if you cant avoid it. Now I JBWeld (2 part epoxy resin dries hard as metal) and literally fill in between the frame and engine mounts anywhere its not perfectly flush. This welds the engine in place.
    This is all before I attach a single bolt or u clamp.

    The next time I do this I want to use those awesome muffler u-clamps and fabricate stronger mounts like ive seen on some other bikes. Relying on the standard engine mounting brackets/bolts etc even if you do all of this perfect still can have issues/fracture/fail etc. I end up using no rubber/insulator at all except for a small thin layer with the u-brackets where they make contact with the frame to keep it from scratching it up.
    Please share any other suggestions/tips.


    First build/bike. "Funhog"
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  11. HeadSmess

    HeadSmess Well-Known Member

    i had one bike, decided to blow its crank seals and die on me... i ended up jumping on the thing a few times, venting.

    the frame BENT before the engine moved :)

    thats how tight they need to be ;)
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  12. Hello Moto!

    Hello Moto! Active Member

    This makes me ask the question..Why does the Skyhawk frame come with the rubber motor mount cushion for the pedestal engine mount? It didn't take me long on this forum to realize that using rubber, especially thick rubber, is a bad idea. You just can't get a solid mount.

    Just a thought...
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  13. Luybaton

    Luybaton Member

    I am having a problem with the stock screw breaking off in the back side of the crank and my other motors piston blew u think I can take that crank and put the other cylinder and piston on? But another thing is the crank with the bolt broken inside is a Z-L (witch is good) crank my other one is some weird gcb1 or something.
  14. KCvale

    KCvale Motorized Bicycle Vendor

    Nice build Learner.
    I just had a repair in here that had those rim lights on it ;-}

    The seat post is the power transfer point.
    You want the engine mount to start there, dead square with the tube and tight, everything else you adapt.

    All the front mount has to do is keep the engine from twisting.
    With a V frame most times it will drop right in, but I build mostly beach cruisers and the front never works.

    I use the SickBikeParts.com front mount system for convenience.

    It's a versatile package, and you will see it used on most all of my 2-stroke builds.
    The trick is to get the right size muffler clamp to fit your front down tube.
  15. bakaneko

    bakaneko Active Member

    Your bike looks very nice especially that tank. Also, how is your butt feeling from that seat... doesn't look very comfortable unless you have really nice roads by you.