Nothing visually obvious when inspecting the cam. turns over fine when cranking engine on starter or by ratchet.
In general (not the Mazda engine specifically), I’d expect to see oil flowing out the sides of the camshaft bearings and flooding the tops of the followers after a period of cranking without plugs (maybe 10 seconds, or so??). Certainly if you’ve run the engine, there should be plenty of oil up there.
There’s definitely puddles of oil in the head. just not sure if it’s getting enough oil pressure at idle. have rigged up a pressure gauge in the block. not the best or most trustworthy setup has don’t have an oil pressure gauge only air pressure. but will hopefully give an idea.
Update: block has 25-30 PSI on the oil pressure when cranking
Update again. exhaust cam for piston 4 has excessive rubbing. the oil on it is very metallic. definitely a problem.
So there is definitely an issue with that exhaust cam or bearing but the oil pressure was alright during crank?
mystery partly sold. either poor oil pressure or blocked channel. good thing i’ve got a spare head.
Those cam journals are not exactly in the first flush of youth either.
That’s good.
That’s Very Bad 
. I don’t think any oil has been getting there. That head is scrap IMHO.
As you say, lucky you have a spare head - figure out why this has happened before fitting it though! 
So: you’re getting oil pressure, but nothing to the cam(s)… I believe the oil feed to the head on these engines is internal - it has to come through a hole in the head gasket. Are you sure that the oil ways in head and block were clear when you fitted the head? Used the correct head gasket? Fitted it the correct way up? (I believe it can be fitted upside down which will block an oil way - maybe what has happened?)
Good luck, anyway.
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Yeah. that’s just on piston 4 and 4 exhaust. both cams are off now and the rest of the cam journals are in good condition and shiny with oil on surface. I think whatever oil vein that feeds those journals was blocked. don’t know if that’ll be in the head or block .
Engines coming out again now will have that done over the week. Will tear down again and find out if its a blocked vein and where.
At the same time will flush all fluids and make sure that none of the metal fragments in the oil from that damage don’t do more.
Will also take the time to make a few choice modifications like the coolant reroute to the rear of the head for a better coolant circulation and also replace the stock oil sensor and gauge with something that gives a real reading.
Does anyone have any other modification recommendations?
Thank you to everyone who’s helped. will be back here once I pull the engine again and find what’s behind this.
FWIW: Just seen on another forum that using a VVT head gasket on a non-VVT engine blocks one of the cam oil feeds. May be something to check…