New Motor Mount

Discussion in 'Frame Mounted Engines' started by Timbone, Jan 4, 2015.

  1. Timbone

    Timbone Active Member

    Well, I broke the motor mount on my GTA-2 pre built aluminum frame. This is complicated by the fact that I have already broken one of the four 6mm motor studs: the one on the rear left. I have successfully dealt with this problem, using a wooden block and metal strapping to hold the back of the motor tight. Still, with hundreds of miles of riding, the smallest front to back spring was enough to break the weld on the mount over time.

    With cold weather having moved in, it's a good time for experimenting. I'll be buying a new motor soon, so I can't really go wrong.

    I did a LOT of thinking to come up with a fix. I bought two thick angle pieces made of thick steel (at least 12g). I cut them so they would make two "L" shapes, using the first "L" to affix to the downtube and resting on the now useless cross member that used to hold up the old aluminum motor mount. I used a 5/16" U-bolt to hold that part on. I inverted the other "L" and affixed it to the first "L" with 4 3/8" bolts. Threadlocked it and it is beefy! It would take a nuke to bust this thing up! I affixed the inverted "L" to the motor with 5/16"Grade 8 bolts and nuts.

    Grabbing the back of the engine is my big problem. My plan is to JAM the engine into a position that nothing can move. I actually had to start with this end.

    I am using two thick stainless steel couplings as spacers. On the right side, with the stud in good shape, I used a bolt and made a kind of cylinder with a tight packing of small washers that squeezed one side of the stainless couple/spacer. The other coupling was filled with 6mm washers that I glued together inside the coupling to make it all easier to handle and to fit up. These two spacers are basically jammed into the bottom rear of the engine, and held together by a 1/4"-20 U-bolt. The U-bolt is not as tight as I would like, but the left shaft feeds up and into the very tight spacer rig (an inner cylinder of washers) and really has no where to go. The right shaft of the U-bolt rides far into the coupling/spacer and won't allow it to move.

    The final step was to attach the motor to the seat tube with carefully measured muffler strapping. As of right now, the motor is tight and cannot move! I'll have to do some extensive testing when it gets a bit warmer.

    The good news in this is that the motor moved slightly forward giving me the ability to take all the slack out of the drive chain. That's it! The Holy Grail of Motorbiking! No need for a chain tensioner. Now all I gotta do is tighten up the pedal chain and adjust the fuel line to optimum length.

    I'll post photos if anyone asks.


  2. Timbone

    Timbone Active Member

    Update: I have locked down the HT 2 stroke motor and it works. The motor is kicked ever so slightly to the left but I don't think this is an issue.

    It has been at least three weeks since the broken motor mount problem. I had to completely remove the engine from the bike to make the new mounting system.

    On my first test run, it was cold and the bike didn't want to start. The exhaust was spitting fuel and it took a while for the engine to really go. I noticed a fuel line leak so I had to give up my testing. Since then, very cold weather has kicked in and I never got a chance to test the engine until today. 3 weeks of very cold sitting in the garage was not good for the motor.

    Today was warm enough to ride! The engine fired immediately, but kicks out a lot of white smoke and has little power. I can go 10-15 mph but that is all I am getting now. The problem, I think, is rich mixture because if I shut down the fuel line and it runs to empty the bike will accelerate nicely. Obviously, during these moments, the engine is finding a lean condition and the timimg will advance as it should.

    Tomorrow will be a nice day. I'll remove the air filter (home made) and we will see what kind of impact that makes. I have a feeling that the air filter is inhibiting airflow although I have noticed that using the choke doesn't help.

  3. Timbone

    Timbone Active Member

    Update on my update! The motoBeast is alive and well again. The problem with the engine was the air filter; for whatever reason it is choking too much air. Man, the think runs well without the air filter on!

    Oh, well, it is the middle of January anyway. Great day today but I still got pretty cold riding around.