the passage close to the gear end that goes to the oil pump surface is for primary oiling supply. crankcase pressure blows oil through the pump and then through a hose and fitting into the primary. it then drips oil onto the primary chain. not all shovels have that hole...
the angled hole that leads down to the passage behind the oil pump is primary oil return. any pan or shovel engine 65 and later has that angled hole. piston up stroke creates a vaccuum through the gear window while the case window is closed. it draws the oil from the lower fitting port below the clutch area in an aluminum primary case. it will also draw all the other cluch and chian wear grunge into the breather gear... that's most often how the breather bore is damaged... well, plastic breathers eat the bore too.
deep in the breather bore at close to the bottom is a small hole that leads down into the oil air mist trap area... that small boxy looking spot at the lower left of the cam case area. on piston up stroke the breather gear window is closed, crankcase vaccuum draws oil up that passage into the breather gear. that is the last chance for oil to be drawn from the air before it's blown from the case...
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Posted on Nov 7, 2009, 7:38 PM from IP address 75.218.21.126
