I am in the process of fixing some minor problems on my engine, so I have it out of the car and has taken off the oil pan. I found the engine very clean inside, and it appears to have been rebored and the crank seems to have been reground. I found som text written on the crank:
RR
R10
M10

I guess R10 means rod bearings are reground .010" and M10 must mean that the mains are reground .010", but what can RR mean? Is it the engine rebuilders signature? Could it be an abbreviation for something?

I'm trying to think of what it can mean, but since english isn't my first language, I'm turning to this forum hoping that somebody can help me guess.