Shaved the bottom of the cylinder where the scavenging ports are

Discussion in '2-Stroke Engines' started by BikeBuilder43, Aug 9, 2016.

  1. BikeBuilder43

    BikeBuilder43 Member

    Ok. So in the quest for power I thought it would be beneficial to open up the scavenging ports by taking off about a 1/2" of metal from the bottom of the cylinder the width of the scavenge ports. It isnt pulling like it did before. What did I do?
     

  2. crassius

    crassius Well-Known Member

    perhaps left a rough spot or bent cylinder a bit out of round so that piston is now dragging just a bit?
     
  3. Steve Best

    Steve Best Active Member

    Can you show picture or even a drawing?
    I am guessing you widened the cylinder (or engine case?) transfer ports?
    1/2" of metal off anywhere on these engines sounds like a lot to me.

    This could be negative if:
    1) it reduces the crankcase compression (ccr)
    2) the larger cross-sectional area reduces flow speed (fuel drops out of suspension and air loses momentum)
    3) the match or mismatch of ports does not work with the flow and resonance of the engine. Sometimes a mismatch can be helpful.

    Just a blind guess, I'd love to see a picture.

    Steve
     
  4. jaguar

    jaguar Well-Known Member

    ?you shortened the cylinder skirt?
     
  5. jaguar

    jaguar Well-Known Member

    Did you cut the sleeve off at the red dotted lines?
    [​IMG]
    That exists to separate the downward motion of the piston from the upward motion of the intake charge in the transfers.
     
  6. BikeBuilder43

    BikeBuilder43 Member

    Jag thats exactly what i did. Also took a drill bit and widened the transfers a bit
     
  7. jaguar

    jaguar Well-Known Member

  8. BikeBuilder43

    BikeBuilder43 Member

    I did raise the transfers a bit by drilling the middle of the top transfers a bit. I am about to take it apart to see if i drilled the sides. I will take pics.
     
  9. BikeBuilder43

    BikeBuilder43 Member

  10. BikeBuilder43

    BikeBuilder43 Member

    Used teflon as a head gasket. May shave the head a bit more now that i have a sheet of glass and use the stock gasket.
     
  11. jaguar

    jaguar Well-Known Member

    no, throw it away. you've ruined it by raising the transfers too much and angling the transfers towards the exhaust which allows intake to go out the exhaust.
     
  12. BikeBuilder43

    BikeBuilder43 Member

    Good info. Now i know not to put too much effort into this jug. Where can i get a good pre-ported jug?
     
  13. jaguar

    jaguar Well-Known Member

    all the ported jugs are for racing, not for every day street use
     
  14. Steve Best

    Steve Best Active Member

    Jag is right, raising the transfers is a fatal flaw. You could play with it a bit by raising the exhaust port by the same amount as the transfers, leave the basegasket off (use ThreeBond or RTV sealer) and an extra headgasket, but you really have a mess of problems.

    Diamond Back said it well: "One step at a time, you might get there slower, but you'll know HOW you got there faster!"

    You see how easy these cylinders come off? You don't need to do 5 mods at once.
    Pull the cylinder, try ONE thing, and only slightly at that.
    Run it, test it, measure the speed or power.
    Did it get better?
    Now try a little more.
    Wade into the water slowly, learning as you go.

    Want some safe advice for what works without losing any power anywhere?
    Widen the intake and exhaust port only at the cylinder window and maybe 6-8mm into the port.
    Widen the exhaust 1-2mm each side mainly at the top (near head) and the intake at the bottom so each has an almost triangular shape.
    (This increases the pulse signal while keeping port volume reasonably small to keep velocity up)
    Drill out the exhaust pipe flange with a 3/4" inch drill. Be careful! Easy port matching.
    These things will liven up the engine amazingly.
    Some head work and attention to squish area will help.

    I congratulate you for the courage to try. Experimenting is fun when it succeeds.
    Follow the scientific method they taught you in school.

    Steve
     
  15. BikeBuilder43

    BikeBuilder43 Member

    May go with a thatsdax kit. I heard they are balanced. Dont know about reliability. Not the kit. Just need the engine and a smaller rear sprocket. I wanna do a 32T again. Loved cruising at decent speeds with relatively low rpms. My bike has a really bad vibration issue and I've had to modify the mounts a few times already. I am gonna go with better hardware before I put it on too.
     
  16. pghewins

    pghewins Member

    what the feck did you use a chainsaw lol
     
  17. BikeBuilder43

    BikeBuilder43 Member

  18. pghewins

    pghewins Member

    as someone said earlier you have to be precise and acurate hacking out metal will invariably make things worse i have worked for bar f1, mclaren ,renault, ducati, aprillia and honda and all power gains are made from very very careful engineering im only into these because my son wants to play with one unless you have an airflow and air speed meter and a means to monitor what you are doing and the effect it is having on air volumetric speed intake and try and port your engine invariably you will feck it up and reduce airspeed and vorteces effect the kit cost hundreds of thousands of dollars best bet rip it out start again gently this time if you do not know how to use a die grinder use a file if it your hobby you will get more satisfaction and at the end a batter and more acurate job
     
  19. BikeBuilder43

    BikeBuilder43 Member

    I am gonna get another kit. Gonna at least port match and clean up the excess metal. Not gonna go all out this time because i have very little experience. I had it running REALLY strong for a while before i screwed things up. Felt like a little powerband in the mid to upper rev range. First time i got that result out of any one of my builds
     
  20. Steve Best

    Steve Best Active Member

    Yeah, go slow, a little at a time.
    Don't port match the intake. Will make it slower.
    The "means to monitor what you are doing" is testing it on a hill with a repeatable speedometer or tach.
    Do a slight mod, test, go more or back off depending on the results.

    Steve
     
    BikeBuilder43 likes this.
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