John Deere 110 tlb loses oil pressure

[gravedigger2]

I have a 2011 JD 110 tlb it has a yanmar diesel I had a overheating problem that required the engine block to be machined and a shim put in between the block and head. All went back together good starts and runs good. The problem is it doesn't build good oil pressure only about 20 psi cold and after 10-15 minutes it loses oil pressure slowly. I was thinking it could be a bad or pinched oring in between the engine and the oil pump pressure side any suggestions would be appreciated. Planning on pulling it apart this weekend

 

[cormier]

Did you replace the main bearings when you got the block machined?