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That's very interesting Jim. I will have to check the pistons for comparison - mine are 1982 and the others I'm not sure, but most likely 1980 - 81.

A very related to all this a couple questions. In my project, all will be new: new rings, deglazed cylinders, new valves and machined seats, new seals.
I will definitely need breaking in time for the machine! What is recommended by experienced users? On one hand, I know you shouldn't push the engine beyond certain RPM until a certain mileage is met. Then it's recommended to operate the engine at a variety of speeds, not a constantly similar rpm's. What worked for you did you find in practice with these bikes?

The second question is, which engine oil to use? People are raving about Rotella T 14W-50 diesel. I am using it now in Vmax and Goldwing. All works great, but I think the clutch worked somewhat better using the native Yamalube 20W-50. Vmax doesn't like synthetic oils because of clutch slippage.

OH NO - Not the "Oil" thing again ?
...and so no one is offended -

LOL This is the FIRST time for me to talk KZ13 oil!
Isee.... One more reason to make it quick, short. and sweet
So.. what oil do you run scotch?

Considering the "Shell Rotella" now I have new valve-stem seals and can keep oil IN.

They sell it in a big bucket. Becomes quite reasonable when you buy it. I couldn't find any in depth discussion on oils on the forum using the search box... maybe I should stick to the Rotella?... hmmm