New guy with a lawnboy

Discussion in '2-Stroke Engines' started by Lawn-boy, Jun 30, 2009.

  1. Lawn-boy

    Lawn-boy New Member

    Hey guys, i have started putting a 2 stroke lawnboy engine on my bike. Its around a 4 hp. Its all bolted together. The engine just has too much compression and the crank is slipping on the wheel. What would you guys recommend (without purchasing anything online) to use for a friction drive? If i put a bigger wheel type thing on the crank would it help? Once i get the drive train all solid i will shower thy mods down upon the engine...pipe..porting..etc thanks

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  2. Happy Valley

    Happy Valley Active Member

    Hi there, good start. A second brace on the left as well to hold steady down pressure might be a good idea. Drive spindle size affects gearing, larger spindle more top end but lower torque for climbing. BMX pegs can be adapted.


    ps
    you might want to downsize your pics.
     
  3. Hawaii_Ed

    Hawaii_Ed Member

    wow, cool homebrew! I have no idea what to tell ya on the drive, but be careful not to get your shirt tail in that flywheel LOL!
     
  4. Mountainman

    Mountainman Active Member

    nice
    would like to watch this one come along
    many have used a skate board wheel for the friction
    some take something like what you have and make an epoxy mixture with sand mixture added
    MM
     
  5. Lawn-boy

    Lawn-boy New Member

    Well a bigger drive gear would cause the engine to turn over easier ,correct? Im sure this engine has more than enough oomph to to push along at low speed without trouble.
     
  6. Esteban

    Esteban Active Member

    Be advised,,, that's a LOT of motor for a bike ! TOO much, in MY opinion.
    But, if you insist, I agree, a brace on the other side is absolutely a must. It having so much power, you will see that overrevving IS going to make the drive roller slip. Maybe make a throttle stop to keep the rpm's down. You can buy a cheap grinding wheel, like you add to the end of your drill, put it on a table, wear safety glasses, cover grinding wheel, & beat it with a hammer. Take the fine powdered bits, & mix with JB Weld. Apply A LIGHT coat to the driveroller to get a better grip. Save remaining bits, for another coating later. It will take a little trial & error to keep from grinding the tire up too much, but you will get it.
     
  7. Mountainman

    Mountainman Active Member

    larger friction drive wheel - makes for higher gear - faster top end speed
    not the best for slower speeds
    not the best on hills

    turn over easier ?? not really

    MM
     
  8. Lawn-boy

    Lawn-boy New Member

    Almost no hills where i am. It would make it turn over easier, its just like a motorycle, if you try to push start a cycle in low gear its hard to get the engine to turn over, shift it into a higher gear and it spins over a lot easier. I own 3 dirt bikes and ATC's so i'm fairly experienced with the engines.
     
  9. RMWdave

    RMWdave Member

    word on the easier starting<bigger wheel.

    i used to bump start my old tri-moto in 2nd
     
  10. seanhan

    seanhan Member

    I wonder

    If you can just put the rope pull back on and start it that way ??
    most rack mounts use the starting rope....
     
  11. duivendyk

    duivendyk Guest

    You will have a very hard time getting this thing started,it is my guess around 100cc or more.I did an approximate calculation of how much continuous force it would take at the pedals and came up with something like 150 lbs plus to overcome the compression of the engine, and that was assuming a 6" roller .It would require a down force of at least 80 lbs on the roller to keep it from slipping.Does not look practical to me.With that 6 roller size you would be doing 33mph at 3000rpm.
     
  12. RMWdave

    RMWdave Member

    ^ hehheh in other words bro, put the recoil on it
     
  13. Lawn-boy

    Lawn-boy New Member

    I dont have a recoil. I dont plan on getting one. I got it to turn over. Just need a new carb.
     
  14. RMWdave

    RMWdave Member

    cool. why do you need a new carb?
     
  15. Lawn-boy

    Lawn-boy New Member

    Original is a bowl carb. I have a diaphragm tilly, but its old and needs a rebuild kit. I might as well buy a new one.
     
  16. RMWdave

    RMWdave Member

    id stick with a bowl type carb for this type of application, diaphram carbs can be a pain in the junk when it comes to varying throttle positions.

    you should look into the dellorto replicas (if you have a round manifold to slide it onto) or if you really want to stick with the diaphram the walbro 603.
     
  17. duivendyk

    duivendyk Guest

    I made a mistake in my calculation (crank dimension is 1/2 of stroke not equal to it!)That changes things somewhat. I takes 100lbs + at the crank to turn the thing and about 50lbs+ roller pressure to keep it from slipping.That is with a 6" roller,more with a smaller one!.You need a compression release,to get going (not feasible on 2 strokes).I should mention also that I assumed a 2:1 ratio between front & rear sprocket,if this was reduced to 1:1, the requirements would be cut in half (or the roller size reduced to 3" from 6)
     
    Last edited by a moderator: Jul 4, 2009
  18. RMWdave

    RMWdave Member

    why isnt it feasable on a 2 stroke? man i have CM cutoff saws at work that have compression relases to start them. i fix them 8/10 times they get rented out because people rip the recoils off them trying to start it without em. and they are only 60cc!
     
  19. duivendyk

    duivendyk Guest

    You are quite right, a compression release not infeasible in principle on a 2 stroke,that's true,but is rarely seen on lawnmower engines as far as I know.How is it implemented, a spring-loaded valve in the head?.It would appear smart to enlighten your customers about this very nice feature!,IMO.
     
    Last edited by a moderator: Jul 4, 2009
  20. RMWdave

    RMWdave Member

    lol well tell em... they never listen haha

    all it is is a little sealed plunger in the side of the cylinder! pretty cool!
     
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