piston orientation. which way does it go?

Discussion in '2-Stroke Engines' started by daninthesand, Jun 8, 2009.

  1. daninthesand

    daninthesand New Member

    Does it matter?

    My second build is going ok. SBP shifter is in. This is a new 49cc slant head taiwanese engine. I took off the jug? (is that what you guys call it?) to look see what the ports were like. Dummy me never marked the piston. I cannot for the life of me see any reason it should go back in any particular orientation either way it looks the same. I have found references to marking the piston before removal and am now concerned I might put it in the wrong way.

    I have searched in vain to find a previous thread about this but i am sure there is one.

    Any ideas?


    ps. I did figure out that the piston goes in so that the flat side of it goes up toward the spark plug. duh!:whistling:

    pss. The needle bearing is really sloppy by my guestimate. Is this normal?

    thanks again.

  2. Flapdoodle

    Flapdoodle Member

    If by sloppy you mean moving side-to-side, yes. Some of us make spacers for the wrist pin to keep it centered.

    Mine is nylon, another fellow used brass tubing.
  3. machiasmort

    machiasmort Active Member

    Acreguy would be the one to ask.

    My best guess would be to put the piston retaining ring pins (facing toward the carb). That means that that side of the piston will be under preasure while returning to top dead center. I might be wrong so ask AG!

    Wait a minute. I read your post again. You took the jug off or you took the piston off of the connecting rod? Or is it both?
    Last edited: Jun 8, 2009
  4. Old Bob

    Old Bob Member

    On any two stroke rhe rings locate so the ends don't drop into exhaust port. or any other port.
  5. daninthesand

    daninthesand New Member

    Good point. Yes it is sloppy side to side, but I meant that the needle bearing itself appears to be too big for the pin....hmmmmm... i just thought of something. I suppose the bearing would be sloppy if just sitting on the pin without the rod attached right? :whistling: I'll put the pin/bearing/rod together and see if its better....I'm learning as I go along...sorry...but I have to say this is fun!


    I did think of that...hence my confusion. The ring ends don't drop into any port either way around! :jester:

    Thanks for help guys! Bummer...i got grease on my keyboard....:D
  6. biketec

    biketec Member

    The piston goes in either way as for the rings there's a pin in the ring slot top ring half moon down, bottom ring half moon up.
  7. fetor56

    fetor56 Guest

    It's preferred(but not essential) if the piston is orientated the way it came out the barrel...that way u won't get a new set of wear marks.
    Is there something on the engine that makes u think it's Taiwanese?
  8. wildemere

    wildemere Member

    The piston ring locating rings are roughly 90 degrees apart and face the inlet side.
  9. BSA

    BSA Guest

    Hmm on mine theres a small arrow which should point towards the front of the engine.
    If not I would just look at the jug and decide which way the piston doesn't snag any ports. If you put the piston in the wrong way you will snag a port and break your rings.

  10. daninthesand

    daninthesand New Member

    The engine is new so has no wear marks. I probably should have said "chaiwanese" . The motor is a typical Chinese made one, if one judges by all the Chinese writing on the box.

    I will place the piston like wildemer said. either direction the ring pins don't line up with any ports. So i think i got it covered at this point.

    The piston does have a mark on it but it simply is a "3"

    Thanks everyone.