Vintage BMW Motorcycle Owners

Wow. What an article!
I really appreciate the time and information.
I will learn what you have written here.
I already know that I will consider replacing this rear bearing with a barrel roller type.
Updates will follow.

The barrel roller bearing is quite expensive, and may not be worth the cost for the relatively low-stressed R51/3 engine. But that’s up to you to decide. Also, you will need yet another tool, a bearing aligner, to install the crank back into the case. It’s a very simple tool, no moving parts, which can be easily made on a lathe.

Many reputable engine builders don't even use the spherical rear bearing even in the R69-R69S engines it was designed for. A standard front and rear crank bearing is quite fine for an R51/R50.

Dave