Gary
I looked at the crank pin under magnification. I thought I could see little lines around the diameter. I tried a little oven cleaner that I use to clean the window on our wood burning stove on it. Then I scrubbed it with Scotchbrite. After a good water clean, I could feel little groves with my finger nail. They are very hard to see but I think I can feel them. Next, I pulled a similar looking crank shaft from my parts box. I think it was from a 56. Rubbing my finger nail on that crank pin felt much smoother. I looked up the part number for the crank on the 50 and 56 and found out it was the same part number. I am not going to put the original crank shaft back in the engine, I’m going to use the spare one I had.
Interesting side note… The threaded section of the replacement crank shaft is about ¼ inch longer than the original one that was in the engine.
Since the replacement crank shaft came from a bag of parts I bought at a swap meet, I did check the run out with a dial indicator. I have no idea of its history. It was good to go.
I think the oven cleaner trick saved me from using a crank shaft that may have caused a problem further down the line.
I now have the lower part of the engine assembled with new bearings. All I need is the new con rod to come in the mail.
Pedro