B A L D E R D A S H ...We go through this discussion periodically...
There are very few engines using roller bearings on the crank, US 41 and old Q35s and 40s..
They have a bronze thrust washer to take up the longitudinal thrust, and it works very well and for a very long time..Most of these old engines are still running, outlasting the planes they were put on..
Maybe someone can ENLIGHTEN me as to why DA, for example, using ball bearings on the crank, is better suited for thrust than a CHAINSAW or weedeater engine using the same ball bearings ? The crank in both types is pulled against the front of the case by the prop..THRUST...
The main difference between a CHAINSAW and a DA is in the porting of the cylinder..The DA is designed for more torque at lower rpm, while the CHAINSAW wil run happily all day long at 8000 rpm cutting trees...
Any bearing engineer will tell you that a BALL bearing will take about !/2 of its rated load in thrust...I con't know of any model airplane engines that will put 1500 lbs of thrust on the crank...Cantilever crank engines, like the DA 50, use the REAR bearing to take up the thrust..Engines that are not cantilever crank types use the FRONT bearing for thrust, The rear bearing is there to support the rear portion of the crank.....
BTW, almost ALL the model airplane engines sold in the past 20 years are mostly CHAINSAW or WEEEDEATER derivations...