I have got a vespa 50s, and I bought a new mazzuchelli amt120 crankshaft. Only it doesn't fit nicely, it touches the bulb at the inletport. I compared the circle diameter of my new cranshaft with the circle diameter of my old crankshaft.They are respectively 86,85mm and 86,15. Is the new mazzuchelli not ok and should I exchange it with another one. Or is milling of the inlet port bulb necessary.