Generator Guru Says:
These can fail due to sun damage, age and the vibration of the engine. If one has failed we suggest you check the others for cracking as these might also fail. If they do, this creates bubbles in the oil which decreases the effectiveness of the oil and can result in engine damage.
** If you think your engine is vibrating too much, hard to turn over with the recoil or making a "popping noise," it is time to reset the Valve Lash Clearances. Check out our video on YouTube to see how to perform this service. https://www.youtube.com/watch?v=mYrdnPVmaDs