The diameter of the seal surface on a stovebolt crankshaft is 3 7/8 inches. Back when we were changing a couple of those seals a week, GM had a tool that was used to pack the rope into the groove in the cap, simply a half circle of steel with a handle on it. I made a similar tool out of an old 4" piston, turned down to 3 7/8" diameter with a piece of wooden dowel rod through the wrist pin hole. Use it to pack the well-oiled rope firmly into the groove and trim the ends off flush with the cap. Silicone sealers weren't even thought of 50 years ago when I was installing rope seals, and they didn't leak. The seal I installed in a 261 we rebuilt six months ago isn't leaking. It's all in the technique you use.
Jerry
