all engines will vibrate a little, especially a 2 stroke engine. i wouldnt worry too much about it. take the spark plugs out and remove the pto cover. turn the engine over by hand. if it is easy to turn over by hand, chances are your alignment is correct. this is not the be all end all test, but a good rule of thumb is to try that. if everything moves smoothly with no binding you should be good. if the shaft and engine arent aligned, it will bind and you will feel resistance.