As posted by Konrad:
There are predominately two types of bearing failures. First type of failure is over loading as a result of poor size and type. This kind of failure would need to be discussed in context with individual model types.

Please note that as the contact area is increased (ether by design or overload) the skidding across the ball increases causing heat build up with the eventual spalling of the ball. This is because of the different surface speeds on the balls surface as a function of the radius distance away from the axis of rotation.

The real concern in our toy engines is corrosion, and galvanic corrosion to be specific. In our engines we have a ferrous steel (bearings and crankshafts) in an aluminum case. These dissimilar materials combined with moisture effectively make a battery. This battery action accelerates corrosion both in the aluminum and ferrous material. Now just about all our toy engines are made from aluminum and ferrous materials. So why does the OS engine fail bearing at a higher rate than some other quality engine? Well it has to do with the aluminum alloy OS uses. OS has chosen an alloy that is both easy to injection mold and machine. Better engine companies such as Rossi use an alloy that is a little more difficult (not much) but has a lot higher tool wear rate. This alloy makes for a much stiffer stronger case with the down side of added machining cost as a result of needing to change out the cutting bit more often. Rossi and many of the other higher quality engine manufactures have chosen an alloy that is better suited for us the end user than the demands of the manufacture.

So what does this have to do with the rusted bearings? Well the aluminum alloy OS use is very prone to galvanic corrosion. This galvanic corrosion is what corrodes the OS bearings. So the root cause for OS’s high corrosion rate of her bearings isn’t so much the bearing material as it is the aluminum used in the crankcase.

Now some of you will say, but after I change my failed OS bearings with brand X the new brand X bearings last a lot longer. This often is very true. The reason for the second set of bearing to last longer is because as aluminum ages (corrodes) it develops an aluminum oxide on the surface. This aluminum oxide inhibits galvanic corrosion to some extent. So older used crankcase don’t corrode the bearing as fast as newly machined OS cases. A simple and effective fix would be if OS would Alodine the cases after machining. (Alodine is a controlled oxide process) This won’t happen as Alodine has chromic acid in it’s make up. Now the uncontrolled oxidation from the galvanic corrosion process is all fine and dandy until it gets so thick as to start to come off the surface. This liberated aluminum oxide will fail bearings, as aluminum oxide is one of the harder abrasives. So while a microscopically thin layer of aluminum oxide is good too much of a good thing is bad! So I contend that OS is blaming the end user for failed bearing when the root cause is the aluminum alloy of her casting.

Also a contributor to early bearing failure is that OS allows synthetic oils. If OS is going to allow the use of fuel that use synthetic lube the engine should be designed for it. In the old days we used almost castor oil exclusively. Engines run on castor oil showed very little corrosion issues. These older engines used bearing often made from SAE 52100 steel. This makes a great inexpensive low temperature (350°F) bearing. But is very susceptible to corrosion. The use of 440c stainless steel is often called out for bearing in a corrosive environment. The problem with 440C SS is that only has about 80% the dynamic load capacity of SAE 52100 steel. So if the original design has marginal dynamic load margins the use of stainless steel bearing is not recommended unless the bearing pocket is made larger to accommodate the proper dynamically spec stainless steel bearing. In the two examples I gave earlier I machined the bearing pockets, in my engines that hadn’t been destroyed, to allow for a bigger bearing.


Just a side note I picked on Rossi in this post because “Broken Wing” made a false claim in the earlier thread that they were out of business. Please don’t take my comments about Rossi as an endorsement of Rossi over many of the other high quality engine suppliers for truly high performance engines.

Also the use of the term synthetic oil is very broad. I will have to admit I’ve seen very little corrosion in "properly designed" (I'll leave that term undefined) model engine when run on Power Master fuels.