I ran across this on the German einzylinder forum. Pretty cool...
http://community.motozania.com/_1950-BMW-R251-Schuerman-3-cylinder-radial-/photo/15053614/29029.html
Extreme closeup:
http://community.motozania.com/_1950-BMW-R251-Schuerman/photo/15053611/29029.html?enlarge=true
http://community.motozania.com/_1950-BMW-R251-Schuerman-3-cylinder-radial-/photo/15053614/29029.html
Extreme closeup:
http://community.motozania.com/_1950-BMW-R251-Schuerman/photo/15053611/29029.html?enlarge=true