When you press a bearing into a bore, or onto a shaft, it causes the race to shrink /or expand, which tightens the clearance in the ball bearings. This is called preload, and a little is necessary to ensure the balls rotate and not skid. Mokai has an excessive amount of interference fit in the center axle and that puts too much preload on the bearings, add the drag from the seal on each side of each bearing and that is the stiffness you feel. This generates allot of friction which causes more heat than the bearings are rated for. Severe blistering is seen on the bearings seals on a regular basis. This heat causes pressure to build in the housing, that pressure will burp past the seal. When the housing cools, a vacuum is created like in a preserve jar, this will suck water into the housing. The factory front seal only has a very light contact lip which is no where near enough to keep from leaking. There is a collar that slides over the front of the axle with an o-ring inside to seal it, this collar is what rides inside the front seal. The o-ring doesn't provide a positive seal and is something I address in my rebuilds as well.
My method involves removing the excessive press fit in the axle so as to remove the preload from the bearing completely. The thrust generated by the impeller places an axial load on the balls, which will preload them so they don't skid in the race. I also remove all the seals from the bearing so they are open, which reduces even more drag. The stiffness you feel when you get your pump back from me, will be from my front seals only. The bearings are free of preload, to spin without friction, less friction mean less heat and being lubricated with a housing full of oil means the bearings will last indefinitely. With two double lipped seals, instead of one, and with the right amount of lip tension, there is more than sufficient sealing ability to keep water out, and the oil in. It's an overkill really, one seal with the right tension would be fine.
