We sometimes slip fit the left-hand main, particularly on test engines that might be split frequently. We have a simple jig that locks the inner bearing track whilst we mount the bearing in the lathe and then we seal the bearing with grease. We then spin the bearing counter clockwise, whilst we run a close fitting 120 grit flap-wheel clockwise in the bore at about 15,000 rpm in an air die-grinder. 15 seconds does the trick. Just keep the die-grinder nice and square and move it in and out quickly from one extreme of the flap wheel to the other and it will be very accurate. Then just a quick clean out and it’s ready to go.
The only advantage for normal race use is that it makes gearbox ratio changes a bit quicker, when you don’t have to remove anything on the right-hand side. Otherwise we just use a crankshaft puller and installation tool.
Even if you have slip-fitted the bearing or crank, sometimes the dowels take hold, so if your only splitting it once a year you may have to use the puller anyway, then it’s not really of any benefit.