We own a small chainsaw, Sears model 358.357181, serial # 1G311E410. It seems not to have an oil pump, has a small plate beneath the bar, that has a filter, and a 'check valve ?' with the oiler tube going directly to the oiler hole behind the bar. The oil tube was blown clear by air, seems good. The 'check valve?' allows air one way, toward the oil tube, and not the other way, but we do not get oiling of the bar, none comes out. How does it acheive oiling, or does it have a pump? It appears to be gravity-fed. We replaced the bar oil with 30-wt oil, same results.