Chainsaw Repair

I know this is an old thread, but I thought I would share my experience incase it helps anyone.
I had a problem with my oil pump, same as above. After stripping it, I figured it was missing a ball bearing to act as a valve. The oil enters the pump through the gauze. The manual pump draws it on the return stroke, then should push it up the hole that the pic above has a bearing in. I left that clear and I popped a 3.5mm ss steel bearing in the larger hole this side of the gauze.Whilst I was at it, I replaced the smaller ball at the top of the piston valve with a neww ss 2.5mm. Now works as good as new!!
The model is a Mac 4000. 16" bar. Can't fing any info on it anywhere!

Last hope for that saw, befor the extruder come's

yeah that looks like the powermac 380 or the promas440 av the titan models use the same engine but different oil pumps. also there is an eager beaver 2.3 model like that you can usually find for sale on ebay.