Originally Posted by
dinasrt
Not possible, not true Dave. The reason for the hollow in the bolt shank is to prevent someone from over torquing it. Snapping the O.E.M. bolt is better than stripping out the threads of the gear shaft on the S.C. nose! If you have snapped your O.E.M. pulley bolt, or feel that you need to replace your perfectly good O.E.M. bolt, then Rob @ Needswings sells the replacement bolt for you. The bolt he sells is a solid one with no hollow shank, as the O.E.M. hollow bolt is not available new.
I believe you are mistaken, bolts that are meant to shear at a predetermined torque have the diameter reduced by a groove, production wise this is cheaper to do than drilling a hole through the centre of the bolt. The position and width of the groove determines where it will shear. A hollow bolt can twist a lot under torsion and where it breaks can be hard to determine each time.
When the temperature of the air inside the gear section rises it will expand and if there is no hole the air will escape through any gap that there is, with no hole in the bolt the air will push past the bearing and oil seal and blow a fine mist of oil.
The oil will be thrown away from the hole in the bolt due to centrifugal force allowing only air and a negligible amount of mist to escape and thus equalize the pressure inside the gear section to the ambient pressure outside the SC.
There has to be some blowback from the rotors as well through the bearings on the ends of the rotors, any positive seal to prevent this would not last long due to the friction caused by the rotation of the rotors. Dynamic seals are used here as well.
Dynamic seals need lubrication, the oil provides this but the surface of the shaft has to have a certain finish on it to provide little wells were the oil can sit, the finish cannot be too rough or it will wear the seal despite the oil. The surface cannot be too polished or there will be nowhere for the oil to sit. The amount of oil we are talking about in a good seal will be hard to see, some of it will get past the seal in minute quantities which over time will show. It is this oil that lubricates the lip of the seal. The viscosity of the oil is important as well, too thin and there will be a lot of leakage, too thick and it will not sit in the wells on the surface.
The pistons rings in the engine ride on a very thin layer of oil, again the surface finish of the bores and the oil viscosity are critical in keeping the oil in place.
There is a post by Rudy some years back now that explains the reason for the hole, I just added a little more detail as I see it, maybe a little too much detail.
Feel free to point out any errors, I can take it as I am a big boy now. 😉