Discussion in 'Frame Mounted Engines' started by College_Fatness, Feb 17, 2010.

  1. College_Fatness

    College_Fatness New Member

    Hello all, its the Fatness here looking for some guidence on my MB project.

    I have an Electra Staright 8 cruiser that I want to motorize, but have a few concerns I was hoping you pros and bros could help me with.

    1) Engine size. The Straight 8 is a heavier bike and I'm pushing 200lbs. I believe that an 80cc motor will be the best option in trying to climb the hills of BC with minimal effort, but don't want to be prone to overspeeding the bike. Any debate on whether the 50cc will suffice? From what I've read, the RAW engines are the way to go...

    2) Rear sprocket The Straight 8 has a nexus 3 spd internal hub with a coaster brake. Is it possible to get the rear sprocket mounted on the rear wheel? Or am I gonna have to get rid of the nexus for a 1 speed?

    3) I've read the horror stories about coaster brakes. Although I've been riding motorcycles for years and feel confident in my abilities to handle an MB, I am strongly considering mounting a front disc brake system on the bike given the tires are too thick for conventional braking systems. Is that even possible?

    thanks in advance for the info

    Peace and Love

    The Fatness

  2. Dilly Bar Rob

    Dilly Bar Rob Member

    Hello Fatness:)

    1) The 80cc is a good choice for climbing the hills of BC. With the stock 44 tooth sprocket on a 26" wheel my old 200# friend rides up all but one hill around here, and the one he cant make he makes to within 15feet of the top (he doesn't pedal at all, like never). With a little help he could make it. If you want to be sure you'll make it up with no pedaling I think a 48 tooth sprocket would be just right, you don't want to go overkill & loose more speed then you have to. Don't worry about overspeed, the 80 is more about torque then extra speed. RAW? Go with zoombicycles/powerkingshop (ebay)/gasbikeshop (ebay) (all the same seller), they are from Burnaby, have great service & prices, ship free & lightning fast (ordered a kit just 3 days ago and I got it yesterday!). I don't think you would be disappointed with there PK80 kit and if you have any problems Andrew will make it right.

    2)I have my sprocket mounted on an old 3 speed hub (freewheeling not coaster) with no issues, I don't know about the nexus but I assume it's do-able with the standard bore-out sprocket hole/ bend coaster brake arm slightly procedure. Maybe someone else will chime in on that.

    3)as long as you manage to get some sort of front brake on you should be fine, it's just that you shouldn't rely on the coaster alone, especially in a hilly area. Loose the chain and loose the only brake - obviously not good.

    Dilly Bar Rob

    Edit: I just looked at a picture of the nexus, definitely looks like it would work with boring out the sprocket (dremel or better yet die grinder),the brake arm looks to be far out enough that it might not even require bending.
    Last edited: Feb 17, 2010
  3. srdavo

    srdavo Active Member

    I can offer some info on 2 of your questions.

    Use a 48 or 50 tooth rear sprocket, instead of the standard 44 toother. this will help on hills & keep your speed down.

    Adding a 2nd brake is a must. Front disc will be great, but costly!!

    Is this the bike? Beautiful!!!!!


    Mounting a Chinese 2-stroke bike engine to this frame will be a test of your creativity!! New engine mounts will be needed to span the frame.

    Also. this bike has an aluminum frame. Aluminum frames + chinese 2-strokes' vibration = disaster. (cracked & broken frames are common)

    Now that I've totally rained on your parade....have no worries. I'm sure there are other options & someone will be along soon to share them with you.

  4. College_Fatness

    College_Fatness New Member

    Whoops Wrong Thread

    A quick google search on recumbant has informent me that I'm in the wrong thread for discussing my cruiser issues. Will repost in a more appropriate thread

    Peace and Love

  5. srdavo

    srdavo Active Member

    I fixed it for ya. :)
  6. AussieSteve

    AussieSteve Active Member

    Love the bike, it looks great.
    My only contribution is to suggest that, for low gearing, a shift kit must be a consideration, if it will fit the frame and if the Nexus hub is strong enough.
    Then you get the best of both worlds - low gearing for hills and high gearing for the flat and downhill.
    I bought one a few weeks ago and would never go back to one speed now.
    With my 6-speed derailleur gears, I can do 5mph comfortably in 1st at 2000RPM and 51mph in 6th at 7400RPM. I'm in heaven. (And I guess I qualify for the 50mph club, now.)

    As Dilly Bar Rob said, as suppliers go, ZoomBicycles are hard to go past, in your part of the world. I even buy from them from time to time, for delivery to Oz.

    ... Steve
  7. Aussieben

    Aussieben New Member

    Its very similar to my bike, but mine definatley looks poverty next to that one.
    Mine is also an aluminium frame.
    Hope this pic works.


    Cheers Ben.

    PS. By the way, Ive done over 4000ks on this frame and the only signs of fatigue are in the front forks. The rear wheel mount also needs to be straightened every now and then too. I have a 48 tooth front sprocket and a 9 tooth pinion and I still very rarely get into 7th gear. On the flat it will sit on around 50kph (35mph) in 5th and its only a small block (49cc).
    Last edited: Feb 18, 2010
  8. AussieSteve

    AussieSteve Active Member

    G'day Ben. I remember you mentioning that your pedal crank spindle wasn't exactly below the seat tube - that's why I said earlier to Fatness, 'if it fits your frame'.
    Wasn't sure exactly what frame you used, but knew it was a slight problem.
    Looks like Fatness is in luck and can fit a shift kit if he wants and if the Nexus hub can handle it. From that point of view a 48cc might be good - absolute power is less important with gears and the 48 will stress the hub less.
    Don't detract from yours too much, either - it looks pretty good to me. It's practical for your purposes - that's the most important thing. (Mine's set up for shear performance, but heaven forbid I'd ever have to actually carry anything.)

    Mine's an alloy frame too, so let's see how long they last.
    I suspect that a decent alloy frame will last as long as a cheap steel one, at the very least. (Mine's a Malvern Star, not top notch, but not cheap Chinese KMart ****, either, like I would have bought if the motor would fit.)

    ... Steve
    Last edited: Feb 18, 2010
  9. Aussieben

    Aussieben New Member

    The biggest problem with this frame is it seems to chew out the freewheel bearings for some reason, (even HD ones), also every little chain adjustment requires precice front mount shimming otherwise it strips the bolts clean out of the block. You cant mount it very low either as the chain hits the clutch housing. Its actually worn through on mine.
  10. College_Fatness

    College_Fatness New Member

    Hello all,

    So after being repeatedly told that the straight 8 would not function as a MB and realizing how much it would cost for a disc brake and engine mount, I decided to go another way and picked up a manhattan flyer deluxe at the bike shop for 150 bones...It was used. Anyhow, spent a few hours mounting up the engine kit and whatnot, and got her running. My issue, however, is that the chain is rubbing against the fender and the rear tire. The stock chain tensioner snapped off in the maiden ride and is yet to be seen.

    Does anyone know where to get a spring loaded chain tensioner?

    How can I create space between the rear fender/tire and the chain? Do I put a spacer in with the rear sprocket or somehow alter the engine so the primary sticks out more?

    Thanks for the help. Despite my problems, riding this thing is crazy fun

    The Fatness