1986 190e no oil pressure at start-up

[190erebuild]

I have just reassembled a 1986 190e 2.3 liter 8 valve that suffered a catastrophic piston/valve collision. Details were sketchy as to what caused the engine to self destruct. I had the number one cylinder resleeved and replaced the piston, twisted connecting rod, broken valve and guide. I did not tear down the oil pump in the timing case cover when I had it off. The oil screen in the pickup looked clean. On restarting the engine with ~5.25 quart 10W40 natural oil, the oil pressure failed to come up at all. It had an aftermarket oil filter without check valves. I removed the oil filter and back-primed the oil gallery, and the oil pressure came up fine on restart. If I can get initial pressure by backpriming, the oil pressure behaves correctly when the engine is running -- good strong pressure (indicated 3) off idle and normal drop when idling and warm. If the car sits overnight, the oil pressure will not come up on start-up without backpriming the pump.

Yesterday, I got the correct OEM oil filter with internal check valves and got it running with oil pressure. This morning, the oil pressure again would not come up on start-up. I took out the overpressure relief valve thinking that, if I was lucky, it was stuck open and allowing leakdown. It had some slight scoring and was dirty, but it did slide in and out easily. I have not checked the oil filter bypass valve to see if it is stuck open.

I replaced the timing chain and I made one big mistake on reassembly because I didn't realize the timing chain tensioner was ratcheted. I initially installed the tensioner and ran the engine with the tensioner as it was with the old timing chain, way too tight for the new chain. It whined quite loudly until i figured this out and reset the cam chain tensioner.

The car has 65,000 miles indicated but was poorly maintained. It was extremely dirty inside the engine. The piston rings were completely sludged up, for example. Does anyone know what might be causing the oil pressure to not come up on start-up but behave normally if I back prime the oil pump before start-up? Thanks.