Heres how I install a rubber rear main. First things first... Not all blocks can take a rubber seal! take note that the seal groove is centered on the crank journal. there should appear to be even seal pressure on both sides of the crank.. if not, then a rope seal should be used instead.. About half the seal lip should come in contact with your journal that should be polished to 2k grit with no pitting or imperfections where the seal rides. the seal lip of any seal should point toward the inside of the engine. Theres 2 different seals sold for this application... A Brown one and a black one. I prefer the black one because it is stiffer and feels more durable to me, but ive had good luck with both so it doesn't really matter. the brown seals are slightly thicker.
I then pull the crank back out and trim the female end with no flag on a bench grinding stone. I typically want a fingernail thickness of seal sticking up on both ends to give the seal a good crimp on the back side upon cap installation, without distorting the actual seal. Since these engines didnt have a rubber seal, there's no actual formula for how much seal should be sticking up.. It would vary like ring gaps depending on thickness of seal and diameter of journal.. But ive had good luck doing it like that. Then I trim the female end of the seal at an angle slightly so that both seal halfs fit together like a puzzle piece when you put the two halves together like I pictured below... Lubricate the seal journal with light weight assy fluid or engine oil before installing the cap. I use Indian Head sealer on the bottom of the cap and in the corners, so bearing crush isnt impaired. that product and similiar ones have a very wattery viscosity, which is what you want. The side seal I make damp with black silicone. When installing the cap, I leave the side seals handing down about 5/16 of an inch so the catch up flush as the cap is pulled down. you can also add the side seals after cap install, but it can be harder. different side seals are thicker than others, and theres variations in how tightly fitting the main cap is. Main cap bolts are torqued to 110 ft pounds. Steak rods go on the inside