What's the best way to clearance check piston/head/plug?

Discussion in '2-Stroke Engines' started by AussieSteve, Nov 18, 2009.

  1. AussieSteve

    AussieSteve Active Member

    The title says it all. I have a Rock Solid Engines billet aluminium head arriving in a couple of days and I'd like to check clearance on installation.
    ... Steve

  2. I have used a bit of modeling clay. Roll it into a ring to fit around the top of the piston, install the head, rotate the crank to smuch the clay against the head, take off the head and measure the clay. I'm sure there are more modern ways to do it, but this is a tried and true old timey way. Use only a little clay, too much and you won't be able to turn the crank to top dead center (TDC) to get a reading.
  3. AussieSteve

    AussieSteve Active Member

    Thanks motorbikemike45. That's what I'll do. (I remember there used to be stuff called 'PlastiGauge' or similar, but I wouldn't know where to get it.)
    Got my head today! Beautifully engineered. Just hope I can start it with the high compression, (16:1). Tomorrow the fun starts.
    ... Steve
  4. 210061741

    210061741 Guest

    If i remember correctly plastigage is for checking engine Bearing Clearences.
    Could maybe work but the clay i would use.
  5. AussieSteve

    AussieSteve Active Member

    Yep, clay it is. Off to the toy/hobby shop in the morning. I thought about using some of my electronic solder, about 0.8mm, (0.032"), thick, but it wouldn't be thick enough without twisting it together and not as gentle as clay. No need to re-invent the wheel, either.
    Thanks for the help guys,
    ... Steve
    Last edited: Nov 20, 2009
  6. AussieSteve

    AussieSteve Active Member

    In the end, I used Blu-Tak - a small blob in the centre of the piston and a thin ring half-way to the edge of the piston, then smeared the top with oil and clamped the head down. Worked well. (It starts to go gooey if left too long, so pull it back apart fairly quickly.)
    The clearance for the Rock Solid Engines billet aluminium head was approximately 1mm (+/- 0.1 mm) with an 0.7 mm gap in a BH6S plug, for those interested. (Usually I set an 0.6 mm gap, which would leave about 1.1 mm clearance - no worries.)
    Test run tomorrow.
    ... Steve