Can anyone tell me what year my D6 is? The serial number is 5R-4688. I replaced the engine with one serial numbered SP-8B9208. Would like to know the year of the engine also.

The 5R shows that they started making them in 1941 and the next SNs came out in 1947 so yours probably would be about a 45 or 46 guessing as my book only shows start up dates.An 8B is not listed in the book so it doesn,t sound like a serial number. SP means Special Parts so I don,t know what you have, look around and see if you can come up with another number.Look down stamped in the block on the left side close to where the pan bolts up to the block and brush it off good and see if there is a number there.