How to drill piston

Discussion in 'General Questions' started by Neufcruz, Jan 23, 2016.

  1. Neufcruz

    Neufcruz Member

    Finally getting around to getting my gt6 motor ready. I'm installing a RSE reed valve and understand I need to drill the intake side of piston skirt. Anyone have an exact DIY for this?
    Any help would be great.

    Thanks in advance


  2. butre

    butre Well-Known Member

  3. Neufcruz

    Neufcruz Member

    Thanks butre!
    I see many videos but all seem different. Scares me a bit to start drilling or cutting up the piston. Only get one take at it so want/need to get right. Gonna go check out link.
    Thanks again.
  4. Neufcruz

    Neufcruz Member

    Thanks again but still a bit confused. I only want to drill piston and no boost port. Will this still work with the reed valve. I want to go in stages as I learn. Once I get this going right then down the road I can go a little more on the porting etc...
    How exact do you have to be? The one detailed drawing is so blurry I can't see numbers when enlarged.
    Anymore advice would be appreciated, again. Lol
  5. sbest

    sbest Active Member

    Have no fear... Just DO IT!


    This was a well worn Yamaha Blaster piston, donating its life to science.
    You are working on a China Girl / Happy Time engine aren't you? Pistons are only like $10 delivered?
    Buy several and try different things.

    Last night I had my top end off, milled the hell out of my ports and all back together in an hour. These engines have got to be the cheapest, easiest, fastest motors to experiment with EVER. Luv'em!

    Purple Haze and Timbone like this.
  6. Neufcruz

    Neufcruz Member

    Thanks Sbest.
    I've seen so many variations and still really hesitant on drilling. My top hat doesn't come in till next week so I have a little while before I'm ready to rude so I research some more. Did you cut toes windows with a CNBC machine. I only have access to a drill press. Does anyone sell already windowed Pistons?
  7. sbest

    sbest Active Member

    This is a Yamaha Blaster piston that was part of an experiment to see what a boost port in the piston would do.
    All work on it was done in a my home workshop drillpress.

    You will notice it is badly scratched and scarred.
    If you are going to experiment until failure, do it on something cheap, or worn out.

    Also do it one small step at a time to see what works and what doesn't.
    In spite of a well worn and scratched piston and bore, this worked very well:

    My son and I put the piston back into the engine and took it back out for a ride to test the effect.
    Every time we upsized the slot or added new holes, we re-assembled and test drove the Blaster:

    The upshot of this, we learned exactly what and how much made this engine work better.
    This piston was in and out of the engine at least 6 times in an afternoon, with about a half hour of riding each time it was together.
    Notice the plastic shopping bag that assures the clip and dirt do not fall into the bottom end:

    End result was that this was too much, but now we know. Glad we did it to worn out parts.
    These air cooled 2 strokes, with no cooling shroud or cylinder head mount are the simplest top end to work on.
    Only takes minutes to do anything. I can strip a CG engine out of the frame and into pieces in less than an hour.

    So you want to experiment on your new engine? Drill the piston?
    Put it together stock, break it in properly, and order a new piston, or even a new piston/cylinder/head.
    Then is something fails, you are not waiting for shipping.

    But don't let it fail.
    Start out stock, and do your mods one step at a time, so you know what works and what doesn't.


    Just noticed I've got my gunslinger pants on...
    Last edited: Jan 27, 2016
  8. johnsteve

    johnsteve Member

    that piston looks like a Dr Who foe..........A Cyberman i think. I hope your not making pistons to take over the world are you?

    Attached Files:

    Last edited: Jan 28, 2016
  9. sbest

    sbest Active Member

    Oh yeah! It was a bad performing piston!

  10. Neufcruz

    Neufcruz Member

    Do you have a pattern that has worked best. I don't want to have to do this a bunch of times. Any basic pattern to start with? I have a 66cc, dullar carb, high compression head, expansion pipe, reed valve if that matters.
  11. sbest

    sbest Active Member

    Not exactly, I am new to these chinese motors.
    My experience is with Yamaha Blasters, KTMs and various snowmobiles and stuff.
    With a reed valve, intake port timing is not so crucial. Not cracking the piston skirt is.
    I'd suggest a round hole leaving lots of material around the edges of the skirt. At least 6mm.
    But I am no expert and have no experience. The good thing is pistons are cheap for these engines.