Cannondale large down tube.

Discussion in 'General Questions' started by Mountbkr, Feb 1, 2014.

  1. Mountbkr

    Mountbkr New Member

    New guy here .I have a cannondale bike i am installing a motor on . The problem i have is the front mount clamp is not large enought for large downtube. Is there an adapter available for this?

  2. joshua97

    joshua97 Member

    team mate, on emay, or xbox website, of drill the frame an blot right through it
  3. Bzura

    Bzura Member

    If the frame is aluminum I would really avoid drilling through it. I've seen aluminum frame tubes crack in half where a hole was drilled.

    If your local hardware store sells u-bolts get one that will fit around the down tube. Then get yourself a 1/4" steel plate that will accommodate the new u-bolt or cut a 1/4" plate to size. Then use the original plate as a template to drill holes to mount the plate to the engine. Then measure the ends of the u-bolt & drill centered holes for that in the plate.

    New mount is now ready to install.
  4. Mountbkr

    Mountbkr New Member

    Thanks i did some craig listing scored an old Sears Free Spirit for $35 . Definetely not driling any frame for a mount . B Zura idea will be used on my next build depending on how this one goes...
  5. crassius

    crassius Well-Known Member

    I just bought a cannondale a couple weeks ago that was advertised as 'having minor clutch problems'. Got it for $60. Nice bike w/ 24speed auto-shifters, RST front suspension, 6061 aluminum frame and a motor that was unusable.

    To get around the large frame tube, he used a big u-bolt with a flat mounting plate, then to make the engine fit inside frame, he sawed of the front engine mount so it was flat. This left so few threads in the case, that they all tore out : (

    To get the carb to fit, he mounted it on a rubber tube out to the left of the motor, and cut down the clutch arm real short to clear the carb - this arm broke off.

    He used a coat hanger to hold up the muffler when the mounts for it broke completely off the front of the cylinder..

    I'm good at doing these things, and *could* get a motor to fit on one, but it is such a nice bike and so much work, that I restored the bike to working condition without the motor, and will sell or trade it for something more suited to motorizing.

    Lots of luck to you if you try it.
  6. birdmannn101

    birdmannn101 Member

    I bought a larger front motor mount from Sick Bike Parts for $14.95 plus shipping.


    Worked really good too. Just widens it enough. I might still have it laying around since I sold the HT engine.
  7. crassius

    crassius Well-Known Member

    if it's like mine, that tube isn't large it is HUGE - clamp that was on it looked to be an automotive muffler clamp
    Mountbkr likes this.
  8. KCvale

    KCvale Motorized Bicycle Vendor

    Here is my more coherent experienced advice on engine mounting.

    Never EVER drill your downtube for the front mount regardless of what it is made of.
    Just trust me on this, or just think about how sturdy a single bolt going through a flat plate and through a round pipe is going to be against the lateral and twisting forces of a gas engine!

    What is the exact diameter to the 1/8" of the down tube on the Cannondale?
    You can't just put a ruler up on the side and eyeball guess, this is crucial.

    If you can't look it up and don't have a caliper just wrap a tape around it and divide that circumference length by Pi for the diameter.

    A simple muffler clamp for your diameter (probably 1 1/2") downpost and you have yourself nearly 360 clamping power with side bolt tube support and a flat mounting surface to mount something flat to.

    Muffler clamps are like $1.50 at the auto parts store.
    Then all you need is a flat piece of medal with 4 holes; a set to match the front motor mount holes after you pull the studs out, and a set to match the muffler clamp U bolt holes.

    The thing is the chances of just a flat piece of metal is not going to be perfect.

    I found the best and easiest way to do a front mount right is pull the front studs out to start with, and then do the back mount first and forget the front.

    Your seat post takes all the engine force to the back wheel so it is extremely important the engine mount is completely flush with the seat post at a 90 and secured.
    Take this time to get your engine as low as you can, check your chain length to the back wheel... In short get the engine and drive perfect that particular bike, then fashion a front mount.

    On a typical beach cruiser you will find the engine is too low for a flat piece...


    ... Or too high for a flat plate.


    I build for a living and just keep SIckBikes universal mounts in stock.

    It's a clever Z plate design to change the mount distance to front bike mount, it can be mounted above or below the engine and comes with all the bolts and some cool spacers for really far away mounts.

    Hope that helps, I'm off to prep for the Super Bowl ;-}
    Mountbkr likes this.
  9. Mountbkr

    Mountbkr New Member

    Cannondales down tube is 2.229
  10. KCvale

    KCvale Motorized Bicycle Vendor

    Can you post a pic of your bike or a link to the exact model?

    2 1/4" seems pretty big to me, your headset is only 2" and bottom brackets are 2 3/4", SBP's biggest big mount only goes to 2".
  11. Mountbkr

    Mountbkr New Member

  12. Mountbkr

    Mountbkr New Member


    See attached photo . I measured the circumference = 7 /3.14 tape measure in photo just to give you an idea

    Attached Files:

  13. Bzura

    Bzura Member

    I've found it best to first get the proper size u-bolt (or muffler clamp) when mounting a HT to a bike with a really fat downtube. After that it will almost always involve drilling/cutting of a steel plate to accommodate for the wider-than-average u-bolt.

    That's the most simple scenario laid out for you. If you have the ambition & the means you can trim & bend that plate into a z-shape or whatever suits your needs. It's got to be functional first, and then you can deal with making it look as pretty as you need it to be.
    Mountbkr likes this.
  14. KCvale

    KCvale Motorized Bicycle Vendor

    All I can do is suggest one again the very first step I suggested you take, get an accurate diameter and you simply won't get one with that metal tape measure.

    A tool I find I use all the time is just a cheap ($15) linear caliper you can get at Harbor Freight.


    All you need is muffle clamp that size and something between it and engine base with front studs out.
  15. crassius

    crassius Well-Known Member

    mine has the RST front fork and the top tube drops lower at the seat post - I could do it, but the carb would need to be outside the frame to either right or left, and I think I'd make the rear motor mount block much thinner

    I'm not a hobbyist, but rather a maker of cheap transportation, so for me it isn't worth the hassle to make something that I would get about $2 per hour for all the extra labor involved

    I've done similar before tho. so I know it can be done.
    Mountbkr likes this.