We normally see this because of three reasons, one mentioned above which is detonation, another which is preignition(or sparatic ignition, not controlled ignitioned) and an out of balance condition. Sit down some time and do the math of grams at 550 RPM on a balance machine and then calculate at 7000 RPM. Don't be overly surprised. But one thing is for sure, look at the bearings and see what story they tell. And you had better take heed, because it is telling you a detrimental story.
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