With all the recent discussion taking place about the new roller bearings for the IAME X30, it's time to explain a few things about them. First and foremost, they are not a performance gain. This style bearing has been used in the shifter engines for some time now where the abuse is extreme. The results were very good and this prompted IAME to have a bearing specially produced by SKF in the proper sizing to suit the X30 design. This change is all about crank support and stiffness, not more performance.
Reduced big end ovalization.
With the roller bearings the crankshaft runs more aligned, so the crankpin, which is in the center of the crankshaft assembly, remains a lot straighter during operation. This dramatically reduces the conrod big end's ovalization, which is first caused by crankpin defection. Lower rod bearing and washer life is much improved.
No wearing of the crankshaft.
As the bearing's inner rings are pressed onto the crankshaft journals, the journals are protected from friction and the crankshaft life becomes nearly eternal.
No wearing of the crankcase.
Due to the really long lifetime of the roller bearings, the replacement interval is much longer than with the ball bearings. This is a benefit not only for the time savings and cost for maintenance, it increases the lifetime of the crankcase by reducing the wear of the bearing seats in the aluminum, caused by the bearings' removal and installation.
Same high quality worldwide.
On the contrary of ball bearings, where people can use lower quality (less cost) bearings if they want, there are no other roller bearings on the market with the same characteristics as the SKF specially prepared for X30. The users will have the same quality worldwide.
Alignment in general
Better crankshaft alignment also improves the life of the oil seals and provides a more precision meshing of the gears that drive the counter balance shaft.
The only drawback to these new bearings is the fact that the inner race of the new unit MUST have a press fit on to the crankshaft. This is so the inner race is properly retained in place and also because it further improves the stiffness. These bearings may not be used on worn crankshafts where no press fit is available.
A complete assemble / disassembly document may be found on the IAME USA websites.
X30 Main Bearing Replacement Guide
IAME, SPA Technical Representative/USA