Alternative rear crank bearing

[808Airhead]

Check this out, I saved these pics off of FB where I saw a European restorer using this actual roller, not barrel bearing. I messaged him and he mentioned he always built engines this way. He said this was the original design for the war time R75 engine and allows the crank to move in & out rear main bearing inner race vs. entire bearing shifting in the rear carrier and wearing it out. Every engine I have rebuilt, 5 now, have needed new rear carriers dur to this wear. IIRC Zundapp engines use this bearing, and discussing this with some experienced, long time rebuilders, they mention they see no issue with using this setup bearing setup… I am even thinking about it myself! Discuss………

[Seek]

Well, the BMW /2 crankshafts flex quite a bit at higher rpm's. BMW even had to use the barrel bearing in the R68-R69S because of this. I don't know if a roller bearing would be able to cope with this flexing.

[1967 R502]

What is the SKF bearing number?

Is it a barrel bearing? Two row roller? I have also read about those being used.

[DIS295]

Unlike some engines, these boxers have the crank located by bearings at each end, with minimal ability to accommodate for the expansion of aluminum over steel. These use of a roller bearing at one end allows for such expansion. This approach assumes that the differential heat expansion is more important than the crank flex. It's hard to imagine that a roller bearing can tolerate or prevent much crank flexing. There are some that think the barrel bearing in the 69 engines can be replaced with a c3 ball bearing. lots of opinions, less data.

[808Airhead]

All I know is, whatever bearing…. They all seem to spin the crank race / wear it out

[808Airhead]

1967 R50/2….. here is a pic of the #. It is a single roller bearing.