I've finished rebuilding the engine of my motorcycle (4 stroke 650cc single-cylinder). For now it runned only once varying between 1000 and 2000 RPM for 5 minutes with a couple of short bursts after fully heated.

I used Motorex Semi-Synthetic Formula 10W40 oil for that. Now I'm reading various sources of information about how further break-in should be done and am a bit afraid because everyone seems to agree that rings will never seat properly with modern semi-synth oil. It is advised to use conventional oil during first maybe 1000 miles of engine life.

Does anybody have an experience of succesfull break-in with semi-synthetic or synthetic oil? Should I replace the oil with a conventional one immediately? How likely is that these 5-6 minutes with a semi-synth oil have already caused trouble?