This "Window" is made from polycarbonate and comes with hardware as shown. The large pointer lines up with a yellow mark painted at Top Dead Center (TDC) of #1 cylinder. This means that the bottom cylinders are pulled up towards their Bottom Dead Center, minimizing the amount of oil seapage down the cylinders, through the exhaust stacks and on to the hanger floor, also decreasing the likelyhood of hydraulic lock. Another set of marks indicate #4 at TDC and at the firing point of the magnetos. When timing the magnetos, no need to find TDC and the measure again for this spot, it is there every time, in the same place where points open to fire.

The Russians invented this mod, I only improved on it. This is my 3rd version. I have changed the kit for ease of installation, sacrificing a small amount of seapage off the paper gasket for a simple install. There is no oil pressure on the window, lubrication is by "splash",  $150.00 plus shipping