Chains 66cc HT shifts over and loosens chain during riding

Discussion in 'Transmission / Drivetrain' started by aaronreihl, Oct 18, 2011.

  1. aaronreihl

    aaronreihl New Member

    Hey guys, lurked around here for quite a bit and got a HT kit just to play around on and didnt expect any German engineering or anything of that respect.
    I am having a weird problem that I haven't read at all here yet. My HT engine is mounted on a 90s 26" men's Schwinn Mirada Sport. After a ride longer than 10 minutes or so, my motor shifts over on the tube of my bike, causing my pedal to grind into the plate covering the magneto ignition thing, and my chain to loosen. I've tried anything I can to remedy this except Loctite on the head studs before I tighten the nuts and buying a new chain. More inner tube, less inner tube, no inner tube, running without a chain tensioner, shortening the chain, and I've drilled a set screw into the mount facing my front wheel to hold it to the tube. It warped over and I noticed after 20 minutes of riding the screw nearly fell out from the vibrations :jester: . I pushed the engine over with my jacket protecting my hand and tightened the screw back and that got me home.
    Is the solution sitting right in front of my face? I'm thinking I need to buy some loctite (blue?) and tighten the nuts on the studs and wait 2 days or so for it to cure, and then try it out.
    Thanks for any suggestions.

  2. HeadSmess

    HeadSmess Well-Known Member

    make sure the rear mount is sitting square on the frame. shim the front. try a strip 3mmx10x25... rather than wrap something around the tube...

    make a head steady bracket that mounts onto existing cylinder studs and goes to top tube.

    weld the mounts on. replace studs with bolts.

    if its twisting it simply isnt tight enough and loctite isnt going to do a thing.

    some people make a bracket up that goes from the long bolt for the clutchcover/chain guard to the seat tube... depends which way its twisting if that will work...
  3. motorpsycho

    motorpsycho Active Member

    "I've tried anything I can to remedy this except Loctite on the head studs"

    What would this have to do with your engine moving to the left?
  4. aaronreihl

    aaronreihl New Member

    It was just an idea, and I thought it was shifting because of the vibrations moving the nuts and allowing the motor to shift freely. The set screw is working okay, but it doesn't hold up well. I did find an old thread yesterday about the same issue, and it was because of the bike he used. That makes sense, as the bike it's on right now is a lightweight aluminum all-terrain bike. I will try the solution he posted, it looked like he took a piece of steel and bent it into an L and drilled holes in it, securing the clutch housing to the seatpost tube.
  5. Al.Fisherman

    Al.Fisherman Active Member

  6. aaronreihl

    aaronreihl New Member

    Ah yes, that's the picture I saw. Thanks.
  7. HeadSmess

    HeadSmess Well-Known Member

    get a steel frame.

    alloy may just try and kill you one day.
  8. Big Red

    Big Red Active Member


    I think HeadSmess is right. I've NEVER had good luck with aluminum frames. The vibration digs into the soft metal and loosen's the engine and will sooner or later break the frame. I'll still do an aluminum frame for a customer if they insist, but will warn them of the perils of this choice. Rubber mounting helps some, but a steel frame is still the way to go. Bicycle makers use aluminum for the weight factor. They assume you will only be peddling the bike. They don't even THINK for a moment that some crazy people like us are gonna strap an engine to it. I'm sure you will get some that think an aluminum is just fine, and of course this is just MY opinion, GET A STEEL FRAME.
    Big Red.
  9. HeadSmess

    HeadSmess Well-Known Member

    aluminum has no fatigue limit. bend it a little, bend it a lot, it all adds up to reduce its lifespan. a million tiny taps, three good whacks...all the same.

    steel on the other hand, can be bent a certain amount an infinite number of times without failing. once this amount is exceeded, then the lifespan is reduced. a million tiny taps wont do a thing but make noise. 3 good whacks would seriously weaken it but still not fail... four would.

    something like that :)

    an engine at 6000rpm is 100 up then down shakes a second.... addds up real quick...:whistling:

    (dont ask what the piston is made of cus metallurgy is complicated!:shout:)

    and a pushy isnt meant to have an engine on it as red said ;)
  10. Big Red

    Big Red Active Member


    Exactly right HeadSmess. NONE of them were meant to have an engine on them, but if your gonna, Steel is about your only option.
    Big Red.
  11. lazydog

    lazydog Member

    How tight do you keep your chain? I had that problem at first.
  12. Al.Fisherman

    Al.Fisherman Active Member

    Tight enough to leave about 1/2" slack. Don't tighten the mounting studs more then 75 INCH pounds, and install the brace pictured above if you have a torque/engine shift problem
  13. Big Red

    Big Red Active Member


    Al's right Lazydog. If your using a hub adapter and you sprocket alignment is perfect then the 1/2" rule is right. If you're using a rag joint mount then it may not be as "perfect" as you would like. FIRST, Get the rag mount as close as possible. this may take some time but work at it untill you're satisfied it's as close as you're ever gonna get it. I've found the best way to adjust it then is to roll the bike untill you find the tight spot in the chain and sprockets. THEN use the 1/2" rule at that point.
    Unless you've been doing this for a while and have done many, many rag joint sprocket mounts, it is very hard to get it "perfect". If you give it 1/2" at the loose point then your going to have it way too tight at the point where the chain gets tight due to back forth, back forth on the rear sprocket. You will have a little more than 1/2" at the loose point in the chain, but it won't be overly tight at it's tight point. I can get the rag's very close. I don't think I've ever got one PERFECT. I run mine a little loose( notice I said a little) to keep undue pressure off the chain and sprocket. If it gets too tight at the tight part of the process then you can rip out sprocket mount bolts and spokes.
    Of course you can remedy this problem with a hub mount system. Due to the profit margin on these bikes I can't put them on every customer bike I build to sell, But I'm going to start using them on my personal bikes from now on. a hub mount is a MUST HAVE on a M.B. as far as I'm concerned. I here The Old Sarge is now in production and selling a very good one for a good price. Check it out on this site.
    Big Red. _
    Last edited: Oct 28, 2011
  14. aaronreihl

    aaronreihl New Member

    I just did some more research and this bike is actually a steel frame. It's pretty lightweight which led me to believe it was aluminum.
  15. retromike3

    retromike3 Member

    slipping frame

    I had the same problem with my bike and I went with the sick bike part adapter.
    The main problem I had was the seat tube was to wide. so I set up the big tube adapter. I did eventually loosen up, but I only put two nuts on it to see how long it would last before coming apart. I went for about four months before it started to vibrate at certain RPMs. I remembered what I did and promptly double bolted the engine and its been smooth ever since.

    Something else I did was to upgrade the hardware with a grade 8 set from SBP This included all of the parts that touch the engine. I then took all of the mounting hardware (10mm nuts) and double bolted them, working one against the other, I also went down to the hardware store and got both the red and blue lock-tight and went after anything that had threads.

    I got a kings adapter for my Shimano Disk brake hub and guess what? That rattled loose too. Its now held together with helacoils and red lock tight.

    There is something about these little 2-strokes that just loves to vibrate anything that has threads loose, Including fender mounts and stuff you would not even think would be a problem. My advice is double bolt, Lock-tight, lock washer and recheck things before you take off. Its better safe than In ICU.

    Last edited: Nov 2, 2011