I would prbably blame poor maintnance for the gouges, it seems quite common when grass has been allowed to collect in the cooling fins of the engine. If its not using oil, I would run it a few times and leave it be. I hava a 5hp quantum that has the same issue for over 3 years in one of my main fleet that get used all summer and still has not got any worse.
The crank bearings and conrod bearings are not replaceable in these, they are cast into the block/conrod.
Hope that helps
