I switched to Rotella T6 5w-40 full synthetic at the 1,000 mile mark. A lot of what you hear about synthetic motor oil is a myth. It isn't any more "slippery" than conventional oil so you don't have to worry about your rings not seating in or any of that old school non-sense. Many sports cars these days come factory filled with full synthetic like mobil-1. I am pretty sure Yamaha uses a semi-synthetic oil as the factory fill motor oil for all of their products now so obviously Yamaha is not too worried about it either.
I am old school and when breaking in a new engine, I change the oil at 50, 500 and 1,000 miles. I can tell you that I am glad I did the early oil changes on my S-10! The first 2 oil changes were loaded with metal shavings and the oil looked pretty nasty for so few miles. The first 2 oil changes I used Yama lube 10w-40 conventional that I got dirt cheap from a dealer that was going out of business. I could have done the break in with synthetic and it wouldn't have made a difference, it just would have been more expensive each time I changed the oil.
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