mac 320 auto oil pump assy

[Oldtoolsnewproblems]

I had a leaky pump flooding the crankcase. I pulled it apart and I'm clearly not thie first one in there. does anyone have any good photos of the correct way to put it back together. looking at the IPL is vague about how the large oring is supposed to be located, and one of the pistons was installed backwards when i started, so I just need to know how it's supposed to look. the seal is confusing as to how it actually keeps oil out of the case, so I'm a tiny bit nervous theres a piece missing.

 

[heimannm]

The lager o-ring goes in the recess in the crankcase, the rest of the oil pump installs on top and the bail (item 1) holds it all together. If the piston (item 12) or the insert in the pump body are worn they can allow bar oil to leak back into the crankcase. If the outlet check valve is leaking (theoretically non serviceable in the pump body) that can also allow bar oil to drain back into the crankcase, but only if the piston and/or insert are worn.

I have NOS pumps if you decide to go that route.



This is a Mini Mac pump but the 300 Series is very similar, it just has an inlet check valve on the front of the pump body. You can see here that I pulled the insert out of the pump body to inspect and clean the outlet check valve. It is critical to press the insert back to the correct position so the holes in the insert align with the oil inlet line.



Mark