Piston Wrist Pin Dimensions?

Discussion in '2-Stroke Engines' started by Kit, Dec 13, 2013.

  1. Kit

    Kit New Member

    Hi Everyone!

    First post here...I have ran a motorised bike here in the UK since August. I use it everyday to commute 2 miles down farm tracks to my work, and its great. I am modifying it substantially over the Christmas break, mainly to help cope with the 300ft hill on the way into work.

    I need to change the piston wrist pin needle bearing, to cope with the extra compression its going to have to put up with. Its expensive and lengthy importing parts from the US; I'm hoping someone will be able to share with me the dimensions of the bearing (for the 66/80cc engine). This way I will be able to order an equivalent quality part from a UK manufacturer, and have it in a couple of days for a few pounds.

    Many Thanks...

  2. Fabian

    Fabian Well-Known Member

    Why the "substantial" engine modifications when the standard engine works reasonably well and with reasonable reliability, other than fitting a Jaguar CDI, a reed valve intake, a diaphragm carburettor, a CR Machine Manufacturing billet cylinder head, modified standard exhaust system and modified piston.

    No need to change the wrist pin or small end bearing for they won't give any trouble if keeping engine rpm below 4,800.

    For hill climbing and hauling weight, a shift kit is the proper method of solving the problem, whilst maintaining drive train reliability and usability, although i would order the chain tensioners with the kit from the word go.
  3. Kit

    Kit New Member

    Ha! A man on my wavelength Fabian! I had arrive in the post today:
    1. Jaguar CDI Kit.
    2. A 'voodoo' expansion chamber exhaust,
    3. A Walbro Stage 2 Carb.
    4. A RSE Reed Valve .

    I'm expecting good things when I fit all this to my bike. However, (remember I am new to in-depth tuning, and welcome all advice), I have read that increasing compression is important for best performance...I had intended to get a machinist friend to take 1mm off the head, to get additional pressure. I understand that this will take its toll on the stock bearing? I'm hoping that someone will know the bearing dimensions, so I can order it before stripping my bike.

    Thanks for the input...I welcome your additional ideas...
  4. Fabian

    Fabian Well-Known Member

    A most important part to get is the thermal isolation spacer for the Walbro carburettor. Without the spacer, fuel will vaporise in the carby when the engine gets hot; making the bike unrideable.

    You "MUST" get the thermal isolation spacer if using a diaphragm carburettor. There is a good reason why every single chainsaw uses this heat isolation method.

    You can shortcut a lot of setup problems by going here and here and here
  5. Fabian

    Fabian Well-Known Member

    I haven't found the extra gains that are claimed by many using sky high cylinder head compression. My most powerful engine was ironically an engine using the lowest compression ratio offered by CR Machine Manufacturing and then lowering it even more by adding three spark plugs to his 3 hole billet cylinder head, to further lower compression, though i had the Jaguar CDI set at the highest ignition curve.

    I am currently running a medium compression billet CR Machine Manufacturing cylinder head with a centrally located spark plug, but i can't replicate the power offered by the older style (non trapezoid transfer port) cylinder and low compression billet head, much to my frustration.
  6. FurryOnTheInside

    FurryOnTheInside Active Member