INSTRUCTIONS FOR MODIFYING THE TOP OF ZENOAH PISTON FOR A QUICKDRAW PIONEER 26 AND THE 27 +1 mm and THE 27.2 +2 mm STROKER
The top piston crown for a 26 and the 27 +1 mm and the 27.2 +2 mm stroker PISTON are turned down to 1.332" to 1.331". Do NOT cut anything below the ring. Stock crown diameter is approximately +/- 1.337".
FOR A 29, 29.5 +1 mm Stroker and the 30.5 + 2 mm Stroker, DO NOT NEED ANY PISTON MODIFICATIONS. The Best piston to use is the stock Zenoah coated piston.
DO NOT cut more or less than the above dimensions, if you do the engine will slow down.
You DO NOT cut anything below the ring and you have to re-chamfer the top of the crown and the top ring land and when you do this you can NOT scratch the lower ring land. You can't touch the lower ring land in any way or the ring will not seal against it. I made a special file to chamfer the ring land, I ground one side of the file so it has no teeth on the flat side and the edge. Then I polished it on a scotch brite wheel so it is very smooth, this way if you do touch the edge of the bottom ring land it will not put a mark on it. Remember the ring has to seal to the piston just as well as it has to seal to the bore. And before you can cut the top crown you have to put a dial indicator on it and you can't have any more run out than .001" maximum, this means your chuck has to be good and you have to have the piston really well centered. Also the finish that you put on the crown when you cut it can't be too coarse, you have to use a very slow feed. If you need a cut down piston we have them in stock.
Also, you have to check every Zenoah ring with a 10x magnifying glass and look at the chamfer on the top and bottom, 70% of the time one side of the ring will have a bigger chamfer than the other. You always have to put the bigger chamfer up otherwise it will not run very well on top end. If the chamfer is the same on both sides, it doesn�t matter which way you put the ring on.
I can't stress enough how important cutting the piston correctly will affect the power and how it runs. If you are not capable of doing this accurately the best thing to do is purchase a cut down piston from Quickdraw, they are in stock. Also if your piston looks good but you notice the factory lathe turn marks below the ring are starting to wear away, this doesn't mean you need to replace the piston. It will actually run better as these factory turn marks start disappearing.