What kind of motor mount do you use on a 2" down tube?

Discussion in 'Frame Mounted Engines' started by Redneck in China, May 3, 2009.

  1. Redneck in China

    Redneck in China New Member

    I have a Giant MB and am looking at buying a lightweight Giant 23" aluminum frame. It has a 2" down tube. I really don't want to drill holes. I want to mount one of those Chinese 2-strokes. What are my options?


  2. ocscully

    ocscully Member

  3. will_start

    will_start Member

    I am considering getting a new bike and motor,
    and this is the exact problem I have faced as well.

    Most modern moutain bikes seem to have this 5cm/2inch issue...

    I've seen other posts detailing other solutions to this issue previously, but not been
    able to find them...if anyone can find them, post em back here will ya ???
  4. robin bird

    robin bird Member

    All i did was buy longer bolts---unthread the old ones--slightly bend the new longer ones and just put the nuts on these it works perfectly
  5. relaxxx

    relaxxx Member

    My front mount is a custom bracket I made that looks like an upside down T and uses the two original water bottle bolt holes in the frame and bolts to the motor with two more bolts on the bottom horizontal part.
  6. Pablo

    Pablo Motored Bikes Sponsor

    Jim (Ghost0) is working on a new front mount that will fit the larger tubes.
  7. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    It's really simple....you don't need to buy anything

    Bolt a metal plate to the front motor mount that either
    extends up or down from the mount

    Find a suitable wide clamp for the front of the 2" tube that
    attaches to the plate with 2 bolts and nuts

    I don't like using U clamps like muffler clamps as they are too
    narrow and concentrate stress and they look like carp

    Grubee's 50 cc Gen II has an updated front mount that clamps a
    1 3/8" downtube but it can be sanded / filed out to accept about
    1 5/8" as it has about 1 3/4" between the studs
  8. Redneck in China

    Redneck in China New Member

    Thanks for the feedback. A couple of questions though:

    1) The frame I'm looking at is a pretty lightweight aluminum Giant frame. Will the water bottle bolt holes be strong enough to bolt a T-shaped bracket to? I had thought of this but wasn't sure I'd want to put those mount points through that much stress. It is just aluminum.

    2) I like the U-clamp and plate idea. Here's a rough picture of what I was thinking of with the bottom two holes being the holes the motor's studs/bolts would go through:

    l l
    l O 2" between holes O l
    l l
    l l
    l l
    l O O l
    l l
    l l

    I thought I'd just use a 2" muffler clamp with the plate shown above if I can find one. I don't know how hard it will be to find a 2" clamp in China. A muffler shop may have something close though.

    Please let me know what you all think of these ideas.

  9. Redneck in China

    Redneck in China New Member

    The diagram above looks nothing like it did when I typed it so disregard it.

    Basically what it is supposed to be is a plate with holes spaced 2" apart at the top and the holes at the bottom spaced at whatever the motor stud spacing is. This would go between the motor and the u-clamp.

  10. BoltsMissing

    BoltsMissing Active Member

    Here's something I just finished a few days ago.
    The bottom clamp is from the HT chain tensioner, the top plate is hand made uisng electric hand drill, dremel and bench grinder.
    The plate is 5mm mild steel, the blue is "blue compression engineers marking dye" to mark out the punch holes prior to drilling.

    What's being tested at the moment, is I left the engine mount studs original for now( where the cosmetic dome nuts are), so if it snaps I just ezi-out, rather than go through the hassle of trying to drill out hi-tensile bolts.
    If it passes then I might replace the HT studs with the regular upgrades uisng hi tensile allen key bolts.

    Also, if a hi-tensile bolt snaps on the alloy, it does much damage when owners who have ready made bikes, but not "feel" for things mechanical.
    They just keep riding and don't understand minor regular checks and maintenance, things we tinkerers just naturaly do.

    The next mount top plate, if this passes my bolt tests during run-in will be slightly differant, but this seems to work and much engine vibration seems to be absorb by the 5mm steel plate.
    Leather helps absorb the metalics to.

    Attached Files:

    Last edited: May 4, 2009
  11. Redneck in China

    Redneck in China New Member

    Thanks Bolts Missing, that looks interesting. Is there any particular reason for using that arrangement as opposed to a muffler clamp (other than looks maybe)? I lean more toward a clamp for an aluminum frame since it would spread out the clamping force around fairly evenly the entire circumference as opposed to squishing it from the top and bottom. Is your frame aluminum or steel? What dia.?

    I don't know how stout this thing should be. It's just a puny engine, but the frame is aluminum so I want to be really kind to it as much as possible.

  12. BoltsMissing

    BoltsMissing Active Member

    Muffler clamps are for mufflers.

    The other reason is, the botton plate covers more area than a clamp's U-bolt don't you think ?
  13. Ghost0

    Ghost0 Guest

    We have found the muffler style clamp to work very well as a frame mount. We use it both in our Shift Kit rear motor mount and our Universal Front Mount and have had no problems with them in testing or reports back from the hundreds of customers using them. Agreed they are not as pretty as a machined billet aluminum clamp, but one of those would raise the cost way above the average persons comfort level. We do recommend in the instructions for both kits that when using an aluminum frame it is wise to use the stock engine strap to offer added support to the u bolt. As was previously mentioned we are working on a mount to go from the 1.5 to 2 inch tubes. Our current one will only work for the 1.125 to 1.5 range.
  14. will_start

    will_start Member

    Hey Ghost,

    I looked at some muffler clamps at Auto-One.
    They only cost about $4 AU.

    The question I have is how to link the Engine to the muffler clamp ??
  15. BoltsMissing

    BoltsMissing Active Member

    Don't mean to hi-jack ya question Will-Start,
    This method is being done on my own personal use build, a 26" Huffy.
    Uses 2 HT C-Clamps, and leather between the C-Clamp and engine case.
    In the pic it ain't tightened up yet, ongoing buid when time permits.
    I think Zbox sells C-Clamps cheaper than muffler U-bolts.
    Not all HT C-Clamps will fit, some need to be milled out a fraction.
    If too wide a tube, then yes the other easy option is to use plates and muffler U-bolts.
    Some usef muffler U-bolts is last resort, others it's first option.
    So far HT parts can be used in most mountings with some improvising.
    I suppose once it's alll fitted nicely and square you can remove the burrs and rough edges and polish the alloy HT C-Clamp accordingly.
    Note the plate on the back of the far rear HT C-Clamp, important !

    Attached Files:

  16. Redneck in China

    Redneck in China New Member

    Is there any particular reason for using that arrangement as opposed to a muffler clamp (other than looks maybe)?
    Muffler clamps are for mufflers.

    The other reason is, the botton plate covers more area than a clamp's U-bolt don't you think ?

    Muffler clamps look the way they do because the design is an effective way to get a tight even grip on a round surface without distorting the round shape through pinching. This is even more important on a bike frame because the metal is aluminum vs. steel and is a structural part whereas an exhaust pipe is not. Muffler clamps may be for mufflers, but it makes sense to use them since they are designed to do what we want them to do. The only question for me really is am I going to an unnecessary extreme? Do people who use 2" lightweight aluminum frames and drill holes or use other types of mounting brackets experience failures? I imagine failures would be more rare with steel, but I'm talking specifically about 2" aluminum. I've never had a frame crack and break, but I imagine it involves the rider going butt over tea kettle which would be un-fun. I wanna avoid that. As long as it keeps me from busting my precious butt I don't really care what it looks like.

    Thanks for all the feedback!

  17. Redneck in China

    Redneck in China New Member

    A possible solution to all of this?

    Why don't the Chinese engine manufacturers make specific adapter kits for their engines for specific frame tube shapes and diameters? There aren't that many and it wouldn't be that hard. It would really add a lot to the overall product I think.

    Here in China, believe it or not, it looks like very few bikes will take one of these engines as an easy bolt-on. A lot of frames are too short and most others have big down tubes or tubes with weird shapes. One of the only kind of bikes here that the motors WILL fit is the "are bah chuh" (literally "two eight vehicle") like the one in the photo I tried to attach (if it worked). These things are ancient in design with crappy brakes. 10 years ago it was all you could buy here. It looks like they designed the motor to be an easy bolt-on for this bike and haven't given a lot of thought as to how their motors can work on a wide variety of bike types. Can you vendors out there suggest that the Chinese get with the program and give us kits that bolt on, right out of the box (through adapters, different size mounts, etc.) to modern bikes? I noticed that when you buy a shift kit from SBP they want to know your seat post tube dia. Why? because IT MATTERS and they give you a kit to fit YOUR bike. COOL! Why cant the engine manufacturers do the same?

    I'm trying to find a used bike where I live in China and I swear that these kits will probably bolt-on without mods to less than 10% of the multi-speed bikes around here and this is IN CHINA! If they would give us a complete package to start with we wouldn't have to go through all this. Ok. I'm done ranting now.

    Attached Files:

  18. Junster

    Junster Member

    Last edited by a moderator: May 29, 2009
  19. BoltsMissing

    BoltsMissing Active Member

  20. Junster

    Junster Member

    It's the only thing on his site he doesn't have a price on. So I'm not sure. I bought one of his copper exhaust gaskets. He was very quick to ship. He also has the nicest rear sprocket mounts I've seen.