Pre build: weed eater advice

Discussion in 'DIY Home Built Motorized Bicycle (non kit)' started by missle3944, Mar 6, 2012.

  1. missle3944

    missle3944 Member

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    Hi guys,

    While I'm waiting on some torx bits to get the plastic housing off my trimlite weed eater 25cc engine I want to run my psuedo design by you guys and see if you can give me any advice or similar.

    What thickness metal do you recommend? This seems to be the easiest design I can do right now becuase it requires no drilling into the frame. I plan to put a bmx peg on the shaft. I'm going to go friction drive and this is my first build. I cannot fit a 2 stroke in my frame and I'm a little tight on money. I have this weed eater engine lying around so I might as while put it to use!

    The bike with it:

    http://i.imgur.com/TIcAU.jpg

    Regular:

    http://imgur.com/ElOhW
     
  2. BigBlue

    BigBlue New Member

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    Hi Missle,

    here's mapbike's project that might fit your bill. It is simple and doesn't require much money to build. Check out some of the other members friction drive projects - no need to re-invent the wheel.

    http://motorbicycling.com/showthread.php?t=33199

    Good Luck

    Chris
    AKA: BigBlue
     
  3. rustycase

    rustycase Gutter Rider

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    I'd go with no larger than an 1 1/8" drive roller...
    Good luck
    rc
     
  4. missle3944

    missle3944 Member

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    Looks relatively simple, though I don't have a drill press to drill through that solid pipe.
     
  5. a_dam

    a_dam New Member

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    Off topic:

    All the kids around here ride those tiny-framed bikes, but I've never seen any of them without the seat lowered all the way. Even the 6-foot tall teenagers are riding way down low with their knees bobbing up by their foreheads. Must look "cool". It's good to see in your pic that someone knows how to raise a seat to a useable level.

    On topic:

    Rustycase is right. An inch-and-an-eighth is a great roller diameter to start with on a wacker-powered bike. Small changes make a big difference. Over 1 1/4 means no torque. Under an inch will give a top speed under 20 mph.

    You'd be amazed what you can do with hand-tools and determination. I used to clamp my ancient 3/8 inch drill to the benchtop with a wood-jawed handscrew clamp and use shims to get the drill bit parallel with the benchtop. Then I'd feed the material by sliding it on the bench into the stationary bit. You can get some really accurate drilling that way, but it is a pain to set up, of course.

    What thickness metal? What part? Eighth-inch thick steel will be strong enough for just about any part on a well-engineered MB. Aluminum is a lot easier to work with hand tools. Impress us by making all your parts out of bamboo, wood, or paper-mache (and JB weld, of course).
     
  6. NormO

    NormO New Member

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    I'm hoping Deacon will join this dicussion. When it comes to friction drive he knows what he is doing. If he suggests you do something. It's a good idea to listen to him.
     
  7. missle3944

    missle3944 Member

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    Thanks for the feedback guys. Another question is how do I mount the peg on the shaft? do I just jam it on there. I don't have access to a welder either. Could I use plywood?
     
  8. rustycase

    rustycase Gutter Rider

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    IMO... :)

    I think you could cut out a bunch disks with a cup saw and stack 'em on a shaft with some of the hi-horsepower glue now-a-days to laminate 'em and probably run for quite a while.

    IIRC, it was Cannonball2 who experimented with wooden rollers, and results seemed to be promising... but I'd ask him, or run a search on wood rollers and see what comes up.

    ...otherwise... some of the bmx freestyle pegs will thread on to some of the string trimmer output shafts, OR, a washer may be dropped down inside the peg, and a suitable nut tightened up on the shaft to hold it.

    I have a friend who is an accomplished gunsmith with a full blown machine shop... SO, every so often I try to 'stump the machinist' and drop my oddball projects on him... He shaved and turned down one of my Mac flywheels and made me an aluminum spindle, complete with a bearing on the outboard end.
    Nice fellow!
    ...He grumbles every time I show up! Wonder why??? :)

    If you do not have the facilities to do some sort of work, may I suggest a high school or college machine shop class? They are generally open to interesting projects and may take it on, if yer lucky.
    Of course you will be required to pay for materials consumed, but labor is gratis, IME.

    Best
    rc
     
  9. BigBlue

    BigBlue New Member

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    first, take your motor apart and find out what kind up shaft you have - short or a long shaft. From there, you can determine how to mount a BMX foot peg to the shaft or make your own.

    Do a search on what others have done and you'll get a better understanding of what to use as a roller, how to mount the roller and what kind of materials work best for rollers. Also would give you some better ideas how to cheaply make your mounts without spending much money or having many tools.

    As rustycase stated, you could make your own wooden discs and glue them together with a clamp and run a bolt down the middle. You would have to be accurate on your drilling, so the roller would run true. Don't know if it would work until you get the motor apart. Others have glued 80 grit soft backed sand paper to electric motors for traction - might work on a wooden roller.

    Good Luck,

    Chris
    AKA: BigBlue
     
    #9 BigBlue, Mar 10, 2012
    Last edited: Mar 10, 2012
  10. a_dam

    a_dam New Member

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    It's funny you said that, because that is exactly what I just did about a week ago - and it's for my Mac motor too!

    I trimmed the flywheel fins and made a 5/8 OD aluminum spindle to go over the existing shaft. Would have been about a 15 minute job if I had a lathe. And the McCulloch's shaft is about 0.365 inch, so a 3/8 bore would be too loose (my Homelite's shaft was a standard .375 - three-eighths). I also threaded it because there's more than 1/4 inch of threads past the flywheel nut. It was a pain, but it's going to work good. There is more than 3 inches of spindle for me to mount the friction roller and have the outboard bearing at the end. I'll post pics when I get around to it.
     
  11. cannonball2

    cannonball2 Active Member

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    I am running laminated oak rollers exclusively now on my FDs. They work perfectly for my applications which are big bore(97cc) 4 strokes. I built a 31cc WE FD once and the wooden rollers dont have enough bite in such a small size and are hard to make accurately below 1.5". Deacon is the man on small cc WE engine conversions. I think he used stacked washers to make rollers, I believe he even used stacked nuts. If you have a longshaft its much easier to experiment with as you can basically bolt on your ideas. My WE engine ran well with a 1.5" BMX peg, but it was an older(read more powerful) 32cc Poulan. If you are in the 25-30cc range 1-1.25 is best depending on terrain. If I had a longshaft I would find some washers that fit my shaft well and approximated the roller size I wanted and give it a shot. Smooth rollers drive well until wet. All of mine are smooth varnished oak and I can kill the engine with the brakes. Small engines require a good deal of downforce to grip also. Hope this gives you some insights. FDs are cool because they are easily made, are reliable, and ratio changes are a snap.
     
  12. cannonball2

    cannonball2 Active Member

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    Thats exactly how we do R/C engine conversions, turn down the flywheels and make a prop hub from barstock. I convert both short and long shafts. A prop hub would make an excellent roller. The older engines of USA manufacture had good quality bearings. I have never seen one fail even with the thrust loads the prop puts on them. These engines would run long term with out a second support bearing. The newer engines of foreign orgin probably need the bearing. If I were building a small cc FD, I would hit the yard sales this spring looking for older Homelites, Ryobis, Poulans, and maybe Macs. The Macs have ignition module issues which is what put Mac out of business, and a lot of ones for sale have failed modules, check for spark.
     
  13. a_dam

    a_dam New Member

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    Yeah, I've read about the McCulloch ignition module issues. Thanks for the heads-up on that!

    I know that I at least have enough spark for it to run because I was test running it for a while. Compression wasn't as good as my Homey, so I tore it apart for a complete inspection/overhaul. This Mac had VERY little wear and carbon build-up. Might not have even been really broke in before the guy threw it in the garbage where I found it (fuel lines were bad). I just got the Frank Bowman ring in the mail and will be trying it out within the next few days. Those RC conversions are bad-ass, BTW. Especially when the flywheel is replaced by electronic ignition and the cylinder fins are all cut down neat. The motors looks so small and clean. [PIC]

    It's always something, though...

    I thought that it would be quick and easy to swap the Homey off the Schwinn and put on the Mac. The Homelite is still running good, and I might try a new bike/design with the Mac. But I wanted to test it on the old Schwinn, copying the existing design.

    The Macs shaft is different: Messed with that.

    The carb is another Walbro, but the config is much different: Got that worked out.

    Now that I'm getting almost ready to mount things, I notice that the little fuel tank on the Mac is "backwards" (cap on the left). The way the Homey is mounted, the motor is slightly tilted with the gas cap up. [PIC] If I do the Mac the same way, the cap is pointing down. I'd have to put the bike in a wheelie position to pour gas in the tank, and then it would leak for sure with the cap and fuel lines angled down. I can "rotate" things around on the mounting plate, but then I'll have issues with the spark plug clearance under my rack. (I guess I could maybe adjust or remove the rack) Also gotta make sure my heel doesn't whack the motor/tank.

    The way the Homey is set up now, everything works just right. I'm sure I'll get it worked out - at least enough to see how that Mac is gonna work. It's just gonna require a little extra cussin and hair pullin.
     

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  14. cannonball2

    cannonball2 Active Member

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    I have a Mac, but the module was bad and I have never done anything with it. I understand the make very good power and are 31-32cc? The Poulan I used on my only adventure into small cc bikes was a 32cc Pro which has 2 rings and a chrome bore. It made enough power to happily run a 1.5" BMX peg. I would think the Mac Should be similar. The module issues are either a complete failure, or it wont start hot after a shut down, but will restart when cool. I had a Mac WE that had the hot start issue. I just never shut it down until I was completely through. Am interested to see how it works for you. A fellow R/C flier had one and swore it was the best running conversion he had ever had.
     
  15. rustycase

    rustycase Gutter Rider

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    it just occurred to me that a shorter crank from a kiddie bike might resolve that 'heel clearance' problem... since it's most likely the bike won't be used so much for pedalling???
    I find more discarded kiddie bikes than anything.
    rc
     
  16. a_dam

    a_dam New Member

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    That's not a bad idea, rustycase. It used to be easy to find different one-piece cranks to fit these old Schwinn bottom brackets. They're probably not so common today. I really just need shorter feet! After looking it over today, I'll be able to tilt the motor and have enough clearance for everything; as long as I don't try to pedal with my size-12 tippy-toes.

    Cannonball2, I wish my mac was 32cc. It's 28cc with a single ring, but does have a chrome cylinder and pretty good looking parts. Con rod is I-beam shaped and looks forged. Needle bearings on both end of the rod are nice and tight. Crank bearings look pretty much identical to the Homey, and the Homelite bearings are still good after 10,000 bike miles.

    And if the module ends up bad, I have a spare Homelite module. I garbage picked a 25cc trimmer that I thought would be full of spare parts. But the motor was DESTROYED. The cylinder was seized up with metal shavings. The piston was all dented on top like maybe he put in the wrong size spark plug. And he removed the carb before throwing it out.

    But the module looks good!
     
  17. lowracer

    lowracer New Member

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    missile3944,
    For the framework, 1"X1"X1/4" angle aluminum works well or bar (angle won't flex). Also could use 3/16 steel.
    -Lowracer-
     
  18. cannonball2

    cannonball2 Active Member

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    This is from memory so could be a bit fuzzy, but I believe the Mac module was an in house design. I know it has a wierd flywheel design. Most of the other OEMs used Phelon systems and you can swap them around a bit. If the module is white I believe it is the defective one. It may be possible to use a matched flywheel/module from another brand if the shaft fits, probably with some advanced modding. Mac was smart in designing on module to work on most of its hand held equipment. Unfortunately when they began to fail a lot of equipment was affected. If you really wanted to you could go electronic like the R/C engines. Those systems are relatively cheap. They also offer electronic advance/retard for easy start, good idle, and more ultimate advance/power. Will run a LONG time on a 7ah battery or a large lipo.
     
  19. a_dam

    a_dam New Member

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    Of course it's white! Now you got me worried. Maybe I'll get lucky - it's happened a few times before.

    I generally don't start and stop the motor much. I usually motor the 7 miles to town. Then I pedal around in town and maybe hang out by the river. The motor is always stone cold by the time I need to use it again. Still, I would hate to have any unreliable part on my bike - the parts on my body are iffy enough.

    If it is bad that will give me an excuse to try electronic mod.

    Thanks CB2


    missile3944, I didn't mean to hijack your thread. I'll gladly help if you have any more questions on your weed eater build. Hopefully there will be something useful in my rambling posts.
     

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  20. cannonball2

    cannonball2 Active Member

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    On the positive side a dam not all of them failed.
     

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