My 70cc happytime project (many pics within!)

Discussion in 'Photos & Bicycle Builds' started by Bogaurd, May 15, 2008.

  1. Bogaurd

    Bogaurd Member

    Alrighty - I've started a project building up a bike with a 70cc happy time engine which I purchased from www.zbox.com.au.

    I've been working on and off on it for around a week now, and figured I'd share some photos - apologies, the earlier photos were taken with my mobile phone, they're not of the greatest quality ;)

    The bike I decided to build this up on was a 2006 Avanti Escape which I picked up from a local second hand store for $75. The bike was in terrible condition, broken chain, ruined paint, missing brakes, stuffed bearings - you name it. I decided to strip it down and rebuild it.

    Here's the frame when I first stripped it down... (click to enlarge the pics)
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    The chipped paint (this thing was also covered in so many stickers!)
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    I started sanding the paint back, but gave up after 15 minutes & took it down to a nearby sandblasters - for $15 I had the frame sandblasted, and for another $5 they sprayed it with an etch primer.

    Sandblasted:
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    Primed:
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    A light sand later, ready to paint:
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    Painting the frame (hanging on the clothes line, haha):
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    Soo... how'd it turn out?
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    So for $30 I stripped all the old paint & gave it a nice black satin paint job. Nice! :grin:

    From there I fixed up the rest of the gear on the bike, bought a set of brakes for the rear, replaced some bearings, re-oiled & tuned everything - it was all working great.

    A few days later my engine kit arrived, hurrah. I went abut getting it all setup on the bike, I replaced a lot of bolts with hardened or high tensile steel bolts, as the Chinese ones that came with the engine kit seemed to be made of something similar to chalk ;)

    Engine in the frame:
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    As you can see, there was no way the carburettor was going to fit in the frame, there's not enough room. To get around this, I modified the intake so that the carby sits to the side of the engine. This is a temporary intake, I'll weld up a proper one soon :)

    Intake:
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    The bolts on the rear motor mount were replaced with 60mm high tensile steel bolts, and the mount was slightly modified. There's also a bit of black cloth tape wrapped around the frame there to prevent it from getting too damaged.

    High tensile steel bolts:
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    The bottom tube on the bike I'm using is very thick - diameter is somewhere around 50mm. I didn't feel like drilling the frame, so I took a large hose clamp, drilled through it to bolt it to the bottom engine mount, and then tightened it up around the bottom tube. There's some rubber between the clamp and frame for now too, you can see it in the photo - this is actually a very strong mount, and the load is evenly distributed on the tube rather than crushing it at a single point.

    Bottom mount:
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    The wheelset I have on the bike has disc hubs - intended for use with disc brakes - I have a disc break on the front, but the rear stays do not have a mount for a caliper, so I'm using v-brakes there.

    Given that I have a disc hub, which is designed to deal with large amounts of torque, I figured I'd mount the drive sprocket to the disc hub. This gives a much more solid point to mount to, can be mounted with more precision, but more importantly, will transfer the force of the engine to the whole wheel evenly, rather than just the spokes on one side.

    Due to clearance with the rear stays, the sprocket could not be mounted directly to the disc hub. I drew up a simple design in CAD, and took it down to a local engineering firm to have an adapter plate made up to allow me to bolt the sprocket to the disc hub. The hole in the sprocket is also being enlarged to allow clearance over the disc hub.

    The hub:
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    A diagram of the adapter plate mounted:
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    The pink shows where the adapter plate will sit, the green is the drive sprocket, the black lines are the mounting bolts, the white blocks are spacers.

    The adapter should be ready for me to pickup tomorrow, or Monday at the latest - so I'll have the bike finished by then. I've already taken it for a few rides by hijacking the wheel from another bike I own & mounting the sprocket in the conventional fashion, hehe :grin:. The cost of the adapter plate is $30.

    I'll post some more photos & info as the bike progresses more!
     
    Last edited: May 15, 2008

  2. Alaskavan

    Alaskavan Guest

    Good work. That's going to look sharp. Let us know how the adapter plate works. Someone else posted that they had trouble using a rear disc brake mount for their sprocket. The bolts kept pulling out or breaking. There was some speculation, but no real reason why that was happening (possible alignment issue?).
     
  3. Bogaurd

    Bogaurd Member

    Yeah, that sounds a bit odd - there should be no reason that the bolts would break or come out - after all, the hub is capable of standing up to the forces of very sudden deceleration via disc brakes, which would be much more demanding than the limited torque put out by these motors... I'll let everybody know how it goes though :)
     
  4. kjparker

    kjparker Member

    Hey, stupid question time.

    When you removed the forks in preparation for paint, did you remove the bearing races as well? if so, how? I thought they were pressed in, yet it looks like yours are out....
     
    Last edited by a moderator: May 16, 2008
  5. Bogaurd

    Bogaurd Member

    Hey there,
    I did take them out, yes. Mine were sealed bearings, and they were pressed in to some degree. I got them out by inserting a screwdriver down the tube where the steerer would sit, positioning it on the rim of the bearing racer, and tapping it with a rubber mallet. They came out fairly easily. I used a rubber mallet to put them back in as well :)
     
  6. kjparker

    kjparker Member

    can you post more information with regads to your sprocket mount? Im interested in doing the same!
     
  7. With that intake you can get a cool air filter with all the room.
     
  8. redman

    redman New Member

    i did a disk mount adapter and it works great. one step better would be some form of rubber cushioning to take the shock out of the pulse of the motor to relieve the spokes. mine have held in there but its what i see as the weak point. make sure you attach with high tensile bolts though.
     

    Attached Files:

  9. redman

    redman New Member

    your bike is taking similar steps to mine, i like it. i never finished to the level i would like though. stick at it!
     
  10. Bogaurd

    Bogaurd Member

    Hey guys, thanks for the responses.

    I did some more work on the bike this afternoon - I sprayed the engine with a high temperature matte black engine paint, and I fabricated a bracket which mounts the fuel tank over the rear wheel.

    I'll take some photos later this evening and upload them :)
     
  11. Bogaurd

    Bogaurd Member

    Okay, pics:

    Rear mounted fuel tank:
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    The bar that the tank is mounted on is a piece of PVC piping which I shaped by heating up. It's attached to the seat tube with a T-clamp I got at my local hardware store for a few dollars.

    Inline fuel filter:
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    I've also replaced the fuel line...

    Painting :evil:...
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    A better shot of my bottom engine mount:
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    New spark plug:
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  12. rdorman

    rdorman New Member

    boguard, was just thinking with the fuel tank mounted like that, when you accelerate without heaps of petrol, wont all the fuel go to the back of the tank? so there will be air in the fuel lines... or at least vapour. wouldnt want to be running out of fuel every time you accelerate fast =P

    btw, how quick do these things accelerate? and with the 70cc do you need to push off much still?
     
  13. bluegoatwoods

    bluegoatwoods Well-Known Member

    Very nice work and superb documentation of your engineering. (Good, clear photos and such)

    In the future, when doing repairs and such, if you include photos and descriptions like that you can be a tremendous help to everyone here.
    (I'll be trying. But, man, you're already way ahead of the likes of me.)

    I'll be interested in seeing the completed bike. Looks like you're going to have a fine machine!
     
  14. Bogaurd

    Bogaurd Member

    Alright, I picked up my disc hub adapter from the engineering firm that was fabricating it - they did a great job, and it works perfectly.

    Hub adapter:
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    The finished bike:
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    My kill switch:
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    Glad I added a fuel filter...
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    Replaced the exhaust studs with hardened steel ones, then secured the exhaust too - this keeps the engine much more firmly held.
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    A few other pics...
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    So far it seems to run great, though possibly a bit lean. The only complaint I have is that the $4 speedometer I bought on ebay does not work when the engine is running - looks like the RF noise generated by the magneto upsets it, and the readings go crazy.

    [​IMG]

    bluegoatwoods - thanks! I'll be sure to document any more work I do. I've posted a thread on making the adapter plate in the 2stroke section already.

    rdorman - I made sure that the fuel tank tilts forward slightly, to avoid the fuel running backwards when accelerating, though I don't think it'll be an issue anyway. The fuel in the bowl in the carb as well as the fuel in the lines should be plenty to prevent the engine from getting starved :)

    Regarding acceleration, the 70cc pulls quite well when its in its powerband. I generally don't let it pull me from idle, I'll only let the clutch out once I'm going 10km/h or so - I don't like to bog down the motor.
     
    Last edited: May 27, 2008
  15. KiDD

    KiDD Member

    I have the exact same carb mount. Are you having a problem with the tube melting that is attached to the intake manifold?
     
  16. Bogaurd

    Bogaurd Member

    Not so much melting, but it softens under heat, it's a pain. I'm going to have a solid one welded up when I get a chance :)
     
  17. kjparker

    kjparker Member

    wow,thats a tight fit!

    got any pics of the adaptor without it being mounted?
     
  18. Bogaurd

    Bogaurd Member

    Unfortunately no, I was so eager I mounted up the adapter plate before I had a chance to take any pictures.

    As a side note, I took the bike out for a decent ride last night with some friends - at one stage I had my friend driving alongside in his car to tell me the speed. At around 3/4 throttle, I was doing in excess of 45km/h - I think the bike has the potential to do 50-55km/h, I'll try it out once the motor is broken in some more and I'm running a less oily mix (currently 16:1). :grin:
     
  19. KiDD

    KiDD Member

    Mine has started to kinda melt on the edge nearest the engine. The softening of the vinyl made it want to come off until I bought these goodyear OEM style hose clamps. They have a spring that compensates for the expansion of the materials.
     
  20. fastboy9

    fastboy9 Member

    I had the exact same cycle computer and had the exact same problem, only cost me £3 including postage from china but the readings went from 1 to 99, some of the readings weren't even numbers! Will be buying a higher quality one soon though. I must say this is one of the most well documented builds on here, very high resolution images and very clear commentary on everything you are doing. This is a great contribution to the site!
    Fastboy
     
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