I tend to agree with "sport pilot" here... always check all the screws on new engine... especially the head bolts.
I have found them unevenly torqued and even partially loose on more than one of my engines when they were new. Unevenly torqued head bolts are not a good thing, as they can deform the top of the engine case and the liner with it.

In fact, I take every new engine completely apart and clean it thouroughly before I attemp to start it. I have found metal shavings in several engines. Last example was a new MVVS 1.44 twin... its piston pins are closed on one side... there were A LOT of steel chips in both piston pins! Imagine what this would do to the liners and pistons if they start coming out during operation...

After the cleaning I put everything together and tighten all the screws evenly. I also put some synthetic oil on the threads prior to assembly... that saves the threads and helps in getting the screws loose again later.