mounting motor to frame?

Discussion in '2-Stroke Engines' started by snowbanana, Jan 9, 2010.

  1. snowbanana

    snowbanana Member

    I got a grubee skyhawk and the front mount wont fit my bike because the frame does not have the standard sized tubing like really old bikes. I have seen people use a little plate of metal that is connected to the mount and it sits on the tube, but how does it work?
     

  2. AussieSteve

    AussieSteve Active Member

    Like this. Requires drilling the downtube. (Some rubber between things doesn't hurt, either.)
    This type of mount came with my kit.
    [​IMG]

    ... Steve
     

    Attached Files:

  3. stealthc9

    stealthc9 Member

    I dont suggest drilling the downtube....what i did on my old huffy cranbrook was get a u clamp, put it around the exhaust and tighten it to ur downtube, keep your inside stock front mount on it. that will keep the engine straight. and LOCK TITE EVERYTHING.
     
    Last edited: Jan 9, 2010
  4. AussieSteve

    AussieSteve Active Member

    Not sure about the wisdom of that method, either. It places a lot of stress on the exhaust studs. It depends a lot on your frame, I reckon. I'll stick to drilling.

    ... Steve

    A pic:-

    [​IMG]
     

    Attached Files:

    Last edited: Jan 9, 2010
  5. EnFlaMEd

    EnFlaMEd Member

  6. AussieSteve

    AussieSteve Active Member

    I looked at the RSE mount, but it didn't look big enough for my (very thick) downtube.
    Also, I was lucky in that the lower drink bottle mounting hole was in the right place.

    While, in theory, I know that drilling will slightly weaken the integrity of the tube, in my case it is so thick that I'm not too concerned. No problems so far.

    ... Steve

    Two more pics. You can't see it in the side view, but I have rubber between the frame and the mounting plate, to compensate for the angle. Also, rubber under the bolt head and under the re-inforcing plate at the bottom:-

    [​IMG]

    [​IMG]
     

    Attached Files:

    Last edited: Jan 9, 2010
  7. snowbanana

    snowbanana Member

    thanks. those ideas help a lot:grin5:
     
  8. Al.Fisherman

    Al.Fisherman Active Member

    I drilled through the down tube for rhe first and last time...Some can get away with it..
     

    Attached Files:

  9. snowbanana

    snowbanana Member

    I think I'm going to use a U clamp, or something that will wrap around the frame because my down tube is not very thick (barely too thick for the original mount) and drilling might weaken it too much and I know what can happen when the frame brakes while going 30 mph :icon_cry:
     
  10. AussieSteve

    AussieSteve Active Member

    Wow, did that break from drilling? (Can't see the hole from that angle.)
    A neat break, looks like it was sawed through.
    I'll keep an eye on mine. No worries so far.

    ... Steve
     
  11. retromike3

    retromike3 Member

    don't drill or you will be sorry.

    I had a seat tube brake on me because I drilled it. It was cut though like it was done with a hacksaw. I think the vibration of the engine along with the thin tube wall is a disaster waiting to happen. I tried to weld the frame back together with brass and T.I.G. with no success. It kept on braking.
    I finally had to replace the frame and toss my old one out.

    My advice is to keep away from the notion of drilling your frame unless you can reinforce the hole with a welded washer or plate to keep the hole from ripping.

    Mike Frye the bike guy.
     
  12. AussieSteve

    AussieSteve Active Member

    Now you guys have me concerned. I considered getting the tube sleeved. Might go ahead and do it.
    Meantime, I'll keep a good lookout for cracks developing. About 370km and no trouble at this point.
    In my opinion, if this is such a serious problem, the vendors shouldn't be supplying the drill-type mounts with their kits. (That's what prompted me to drill.)
    I've had almost enough of the BS involved with these things.
    I've now heard 2 bad stories, I'd be interested to know how many guys have drilled and got away with it without problems, over a large number of km/miles?

    Ron and Mike, how long after drilling did the tubes break?
    Also, did the crack develop over time, or happen all at once, in one ride?
    And, steel or alloy?

    ... Steve
     
    Last edited: Jan 11, 2010
  13. Al.Fisherman

    Al.Fisherman Active Member

    Steve..the bike that I drilled and cracked the frame probably didn't have 3 tanks of fuel run through it. I drilled the tube to hide some wires, I drilled out a nut that the water bottle rack screws into. Maybe a little to big, I don't know, so no more chances. If for ANY reason...if I ever see one...that I'll need to drill a hole again, I'll sleeve it, braze and drill. I saved the frame ...I repaired it. Also to be truthful...the frame was a thin walled mountain bike, and not that of my Cranbrook Cruiser. That might had something to do with it..I just don't know??? I do have pictures of the repair.
     
  14. stealthc9

    stealthc9 Member

    I didnt put any stress on the exhaust studs, as I let the motor sit there and then clamped it where it naturally rested.

    But I also used the highest grade bolts I could find on top of it. It lasted for over 1000 miles. on to my next bike, and then that bike was stolen.
     
  15. AussieSteve

    AussieSteve Active Member

    Same here. I'll keep an eye on mine for now and will probably sleeve the down-tube when the motor is out next.

    ... Steve
     
  16. Al.Fisherman

    Al.Fisherman Active Member

    Steve...my son was doing 95% of the riding (135#), neither of us noticed anything before it gave out, so I don't know it it happened all of a sudden or not. Thank goodness when it did he was in a parking lot starting it. He said ..it's a ride you don't want.
     
  17. CaptJ

    CaptJ Member

    IMO: I think drilling your frame will make it weak. I needed to increase the height of the engine to clear the chain guard so I made custom mount, works well. Home Depot oak table leg 2.0" X 2.0" X 8.0" for $2.00. On the top of block it has a inlayed 1/8" X 1.5" X 3.0" steel plate with 3 holes in it and came with with my kit. I have 60 miles on it and I think it'll last over 60000.

    have fun ya'll
    Hi, ... Steve ... Ron
    Steve I like your muffler mount I need to do mine.
    ... Jim
     

    Attached Files:

    • 008.jpg
      008.jpg
      File size:
      131.9 KB
      Views:
      129
    Last edited: Jan 13, 2010
  18. AussieSteve

    AussieSteve Active Member

    The wood block is a good idea, Jim. It should absorb a bit of vibration, too.
    That steel plate is the one I used, with an 8mm hi-tensile bolt in the middle hole, going through the frame.
    Wish I hadn't drilled now. I must confess that I know engines better than I do bicycles and their potential weaknesses. Mine's an alloy frame, so I need to find someone with a TIG welder to sleeve the tube for me, within pedalling distance. There are a few metal-fab shops about.
    It could be that mine will never crack, since it is a very thick tube, >2", (the muffler is thinner), and I have hammered it for almost 400km, (240 miles), with no cracking yet. I even pop monos, jump off kerbs and ride on rough dirt roads.
    Still, after all the time and effort I've put into the rest, I don't want to leave such a potentially dangerous flaw.
    Ron, I wish I'd talked to you about this before[/] I drilled that hole. I spent a few hundred dollars on this bike, brand new for the kit and hope I don't have to throw it or replace the frame. Since you mentioned brazing, I guess your's is/was a steel frame. Easier to work with.

    On the exhaust bracket subject, it's a good idea. The mufflers are a bit heavy to hang off the 2 x 6mm studs, especially if they take a bang from something.

    ... Steve
     
    Last edited: Jan 13, 2010
  19. retromike3

    retromike3 Member

    drill update

    Mine failed about on hundred and fifty miles after I installed it and it happened suddenly. One day everything looked OK and the next thing I know my seat tube is rattling like crazy. I pull over and presto seat tube is sawed in half.
    I can't say when it started to fail because I wasn't watching it propagate. I have fixed bicycle tubes on silver brazed bicycle frames before and it usually requires me to cut the tube in half(already achieved here) grabbing one half with a wrench and heating the weld up until it let go. Then if I am lucky I don't need to reshape a new lug or lugs, then I find a tube to replace it with and then copy the length and miter the angles to work with the frame.
    After all that I place the frame in my jig to make sure its strait and level and then sliver braze it back in place. Then I repaint the frame and charge the customer a arm and a leg, because this job is a lot of work! With my frame I did not have that option because it was T.I.G. frame.
    So if you have an option to put an engine on a bike frame by drilling though the main tubes my advice is DON'T.:veryangry:

    Mike the bike guy
     
  20. AussieSteve

    AussieSteve Active Member

    Thanks Mike, we're getting the picture.
    It's a shame there's such a small window for editing posts before they're locked up. I'd like to delete a couple of mine from earlier in this thread, to avoid misguiding people. Still, what's done is done. I hope I don't point anyone in the wrong direction.

    On steel frames, if drilling is essential, a washer brazed to the frame before drilling the hole might stabilize it, I would think. Harder with alloy.

    ... Steve
     
Loading...