Discussion in 'Motorized Bicycle General Discussion' started by salorr33cc, Aug 6, 2017.

  1. salorr33cc

    salorr33cc Member

    Apr 30, 2016
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    My engine that i ordered is a SKYHAWK GT 38mm stroke i believe and uses a type A piston, the enginr comes with a RSE reed valve,, Now i know the reeds wont do a thing unless the piston has a window put in,,

    I dont know where to put window in on the intake side of the piston,, Every Window I see on the internet stores looks different to others,, So Can someone tell me the measurments for the window,,, and also what do i do with the piston skirt that hangs in the intake port when piston is a TDC.. s-l400.jpg
  2. indian22

    indian22 Well-Known Member

    Dec 31, 2014
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    The piston shown has a 1" hole the center of which is located exactly half way between the bottom ring and the bottom of the skirt. On a window piston, modified like this one you would of course do nothing to the intake side skirt as it would fatally weaken the piston at that point.

    I installed that same piston yesterday in a GT-5 motor with a third transfer port cut for a RSE reed valve setup. After riding on and off for about an hour of break in yesterday afternoon I'm liking the 1" piston window mod...the last two pistons I cut windows in were also round & located the same but were smaller diameter (3/4" & 7/8")...the 1" definitely uncovers all of my intake port work & the added 3rd. transfer port milling. Carb used is a Dellorto SHA clone (RT) jetted with a .70 which will probably read too lean, but I'll adjust as I go.

    I've also tried oblong port windows of various dimension that work ok too and left enough room for a slight skirt trim on the intake. The round window is simple to cut and works great, but diameter of the hole has to work with all other engine mods as well. In my case each window in the piston worked pretty well. I just love to experiment & the 1" window is about as large as a 66 cc piston can use & stay in one piece. Good luck!

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