As a positive displacement
pump oil pressure is directly related to rpm
and system restriction. The regulation is simply a pop off valve. Low oil pressure can result from
- Oil pick up blocked or loose - air enters instead of oil
- An internal oil line has come loose or is leaking - your pictures seem to show bolted on oil tubes under the valve cover
- Pop off valve stuck open
- Oil filter restricted, blocked or bypassing - Do you know if you oil filter has a bypass?
- Oil passage
- Failed oil pressure sender
- Gear pump failed
- Oil hiding - Oil hiding occurs when oil is pumped into system and can't drain or return to sump. sump runs out of oil and starts cavitating. This could occur if drain holes from the head are restricted. Oil pools in the head and after shut down drains slowly - Oil pressure will be good at start for a minute or two
The fact that this started after an oil change
could be a red herring or could be significant.
Something could have dislodged during the oil change
. Lot's of sealant
was used (I presume) for pan gasket, front and rear seals
I would remove and check the sender next if not already done so. Most of the troubleshooting for this is going to involve tearing the engine down again and you want to eliminate everything else first.
I would not personally try to run the engine with the timing cover off.