Air-cooled engines have bore tunnels in them for oil.  The boring process at the factory requires end-plugs to be inserted.  With heat cycling of the engne and oil pressure, these can leak or even blow-out.  Here, I drilled and tapped the galley plug-ends for NPT thread plugs (blue hex heads).  Because I did not disassemble the case, I used T-Shirt materials and Grease inside the bores to pull out the shavings once I was done.  The oil pump area was reamed out a bit and I was surprised at how bad the casting tunnel was in the ports to the oil filter, bypass valve and oil cooler.

 

The push-rod tube holes show the lifters sitting in there (they looked great), and I used the same grease rag technique when I polished those with 400 grit wet/dry paper.  They were sort of "orange-peel" textured from the original casting and smoother push-rod tube bores prevent O-Ring scratches, promote expansion movement and thus prevent leaks.

 

Not shown, every gasket and seal has been replaced with new gaskets and sealed with Curel K2.

 

Flywheel and transmission end: