Jonsered 920 air leak- need help

[A_sharp]

I finally started to strip my saw down to split the crankcase and find the internal air leak but have discovered the oil pump is open to the crankcase body. When pressure testing it seems possible that the air could be leaking through the oil pump assemply into the oil tank and exit through the tank vent. Before going further I need to check the oil pump for leaks but can't think of a way to pressure test the pump assembly. I am planning to dissasemble the pump to see if there are any orings, seals, etc that appear to be damaged and potentially causing the leak. Anyone have similar problems and/or suggestions for dissaembly and what to look for?
Thanks, Harry

 

[heimannm]

 

[Bob Hedgecutter]

IF engine crankcase pressure is entering the oil tank- what are its means of escape?
No vented filler cap on these.
So its going to pressurise the tank and escape where it can, you have already discovered the tank vent cotter pin- but is there another exit for fluids/air out of that tank? Through the pump maybe?
Rather than trying to seal the pump- I would be trying to figure out if indeed the oil tank is being fed with crankcase pressure.

 

[A_sharp]

Success!! I managed to get the oil pump mechanism apart and found the o ring on the pump shaft was worn and loose. This is what seals internal crankcase pressure from the oil pick up line and thus why the oil tank was pressuring up. I do not have the correct replacement for this o ring but got one that was tight on the shaft and reassembled. Pressure tested for 5 min and only dropped from 8 psi to 6 psi, good enough for now. I am on the hunt for the correct o ring, also plan on changing the other o rings if I can find them. Thanks everyone for all your help, you guys are awesome!!
Harry