Broken motor mount stud

Discussion in '2-Stroke Engines' started by Timbone, Jun 18, 2014.

  1. Timbone

    Timbone Active Member

    I've been cruising all over town for the past 2 months, and I have been pretty proud of my moto. The little HT is a runner!

    I've solved countless problems and I am going to be super prepared when I decide to build my next motorized bicycle.

    I was riding yesterday and noticed a loud vibration at 20+ mph. Wisely, I stopped to inspect all the bolts. The rear motor mount nearest the the moto chain had sheared off completely, flush to the engine block.

    My first effort was to dremel in a slot on the stud. Fail. Just wouldn't give. OK, let's try the "easyout" screw extractor thing. Fail number 2. I suspect that I drilled a bit out of line and got into the aluminum. The stud refused to turn.

    I have taken a break to decide on my next course of action. I am not gonna give upon this.

    My complaint is that I have wasted a lotta time I would have prepared to spend riding. I am driving my damn car now!


  2. crassius

    crassius Well-Known Member

    you may be able to drill it out & put in a 6x1.0 helicoil, but if you are too far off center, you may have to drill it a bit larger & tap it for a larger bolt (note that a larger bolt may have problems clearing the frame post, so go no larger than needed)
    Timbone likes this.
  3. Timbone

    Timbone Active Member

    This is great advice and the helicoil was my next plan of action. However, I had to give ONE MORE TRY with the easy out. Drilled in about another 3/16 of an inch and inserted the bolt extractor. This time it bit into the bolt! I felt it give! I slowly cranked and then - POP! - the easy out broke! I burned up my bit trying to get it out!

    So now I am mad. I am throwing out the rule book!

    I've been fiddling around with making a new kind of chain tensioner - still haven't succeeded on improving the kit one! But I do have all kinds of fasteners and metal strapping. Here's what I did:

    The rear motor mount stud on the pedal side is good. I replaced the motor mount and reattached that good stud. The motor mount isn't going anywhere.

    I rigged up some strapping that curls around the seat tube and I found/ created two points of contact. Where oh where???

    On the left side I attached one end of my metal strap to the long bolt that is supposed to anchor the chain guard. That's the top right bolt on the clutch activated cover.

    On the pedal side, I removed the matching screw from the clutch plate cover. I replaced it with a M6-1.0 bolt that ran right into the seat tube. After a lot of cursing and complaining and straining and stretching, I was able to get everything attached! That motor ain't moving!!!

    I was only able to do a 2 mile test run but the bike ran super smooth and quiet. No telling how long I has been running with that broken stud.

    While I am writing, here's what I've learned and how I will incorporate it into my next build.

    1) Will use a 26" wheel model, probably a mountain bike but maybe one of those Skyhawk Aluminum frames. Horizontal dropouts are very important.

    2) 40 tooth motor sprocket for a bit higher cruising speed.

    3) Replace 6mm engine studs with grade 8 studs, if I can find them.

    4) Stick w 415 chain. That thing is tough!

    5)Use tough tires and super tough inner tubes.

    6) Will use at the minimum a run of heater hose or an expansion pipe. Exhaust needs to be kicked out the rear.

    7) A simple but cool water deflector to protect the but from tire spray would be nice!

    8) oh, and I will probably add extra metal strapping to secure and support the engine.

  4. crassius

    crassius Well-Known Member

    I use a lot of studs, so find it cheap & easy to get 8.8 rated threaded rod and cut my own.
    Timbone likes this.