Uh oh! Broken Mount...

Discussion in '2-Stroke Engines' started by solitus3989, Jun 26, 2009.

  1. solitus3989

    solitus3989 Member


    My dad was riding around my motored bike the other day... Said it suddenly started vibrating really bad.

    he parked it, and found out that the bolt had snapped off on the engine mount.

    How do i tap out that bolt so i can remount it?

    I think it snapped because it was resting on the bolt, rather than the engine. pictures included.

    Last edited: Jun 26, 2009

  2. Molotov256

    Molotov256 Member

    Lucky you :\

    That's no fun at all. I did that once, but it's fixable. If you've still got broken bolt left in there, you'll need a few things to get it out.

    -Center Punch
    -Drill/Appropriate Size Drill Bit
    -Bolt Extractor + Tap Handle

    I got mine out using an automatic center punch... it looks kinda like a pen, and you seat the end of it on the bolt nub and press down, it deploys a spring loaded punch to put a dimple in the bolt.

    Then you've gotta drill the bolt with whatever size bit your bolt extractor calls for. Start small and work your way up for best results, and take care to drill straight and center.

    Then use the bolt extractor, which is essentially a left hand tapered bit to twist the bolt out. I got mine out without having to use any heating or torches or anything.

    There's a good article about the whole ordeal here:

  3. Molotov256

    Molotov256 Member

    I noticed too, after looking at your pictures, that the bolt left thread marks on the inside of the tube, so you're probably correct when you say that it broke because it was resting on the bolt. Not sure how to avoid that with that large of a tube, though.
  4. solitus3989

    solitus3989 Member

    First, i updated the third picture. didn't mean to post same picture twice..

    Second, thanks for the advice. Do you think i could grind down the mount a little bit, to make it a little wider so it would sit better? We actually had a pretty tricky time getting it on.. We ended up bending the frame with a C-Clamp so the bolts would clear the side. they BARELY cleared, which is probably why there is so much pressure on there now.
  5. Molotov256

    Molotov256 Member

    No problem... I've gotten a lot more input from this site than I've given!

    I suppose you could grind down the engine mount a bit, but I wouldn't trust my skills to come out with anything I'd trust. I wouldn't bend the tube anymore, either, lest you weaken the structural integrity of the frame.

    Sick Bike Parts sells an alternate style mount for large tube frames. If you're willing to drop $20 or so, it'd probably save you a whole lot of headache. I haven't used one, but other folks on here seem to have had success with them.

  6. use a adapter for a large frame,its a metal piece that bolts to engine then to a c-clamp that clamps around the frame.
  7. MattyA

    MattyA New Member

    i had the same problem. so i got a die grinder and made the mount slightly larger and havent looked back
  8. solitus3989

    solitus3989 Member

    Thanks for the input, everyone!

    My family is pretty handy...

    We will probably be able to make our own large-frame adapter like the one available from SickBikeParts. it doesn't look terribly complicated..

    If all else fails, we have a MIG welder... :sweatdrop:

    Just kidding...
  9. MikeJ

    MikeJ Member

    I had the same problem.... Here is a functional fix I use. For the downtube that is too large in diameter: Borrow and use a large Visegrip locking pliers. Bigger sizes are a necessity. Use it to squeeze the downtube in the area underneath the forward engine mount just enough to form it just under the diameter of the engine mount. I recommend you use work gloves when clamping down. I kept pinching my hand skin everytime I clamped down (lots of pain and foul words!). Now, the gloves get pinched. You are going to have to clamp and squeeze repeatedly to move the tube walls a little at a time. Use lots of liner (paper towel tube, maybe) around the downtube to prevent excessive paint being scrubbed off. The result will be a slightly oval tube, top to bottom, with the top and bottom curve of about the same diameter of the engine mount.

    To fill in excessive gap between the engine and the downtube (optional): Get a set of JB Weld 2-part epoxy. Wrap a layer of wax paper around the downtube where the engine mount will settle. Hold in place with a clamp holding the paper, the clamp dangling underneath. With the engine on the bench, prop it so the engine mount surface is facing straight up. Put a little "fence" around it with electrical tape. Wrap the studs as well. Mix a large blob of JB Weld epoxy on a sheet of wax paper. Popsicle sticks are good at this. Place the well-blended blob into the engine mount fence. Give the epoxy some time to harden from sticky liquid to a clay-like texture. Then take a few minutes to mount your engine into its final resting position on the bicycle frame. (The electrical tape will kinda fold under; it is unavoidable.) The epoxy will form around the contour of the downtube, eliminating gaps. The excess epoxy will be squeezed out. Let it sit undisturbed for 12 hours or more. The wax paper will allow you to remove the engine back to the bench. Pull that off and toss it. Pull the electrical tape off and toss. Use a utility knife to trim off the excess expoxy. The end result should be a non-compressible custom contour to your downtube.

    I found it necessary to double-nut the old too-short studs and remove. I replaced them with Grade 8.8 bolts, 50 mm or longer. Ace Hardware carries a nice selection of metric 6mm bolts and nuts. There should be no more side-contact problems.