After cleaning the engine and replacing the head with a reconditioned head from ebay and a new gasket the engine started.
New injector sealing rings. The official mazda silver ones.
The oil was new. I manuallly lubricated the hydraulic lifters and cam lobes. I didn't put oil "into" the hydraulic lifters. I assumed they didn't need to be primed with oil, that would happen automatically.
Within a short time the engine went from fairly smooth sounding, to tappy. On accelerating there was a knocking sound from the drivers side of the engine. Which quitened down when idling.
When i removed the oil filler cap, i could see a mist of something moving around the area below the oil filler and insider the cylinder head.
No obvious smell from the oil filler cap. The cyclinder head was bought complete from a firm on ebay. All reconditioned.
I have since removed the sump and drained the oil. i've remove the piston rod end caps and inspected the bearings for scoring or damage and they look fine.
I haven't removed the crank yet, so can't say whether there is a problem there.
I'm pretty sure the engine oil is severely diluted despite the engine only running for about 5 - 7 minutes. I'm sure a mazda technician will have seen loads of these failed engines , with the low oil pressure warning and on inspection the exhaust cam lobes worn down to nothing. I'm at a loss as to why the engine is not running smoothly. No low oil pressure warning. No errors on the diagnostic reader. Prior to reassembling the engine, i cleaned all of the internal coolant and oil channels. No debris in the oil pickup filter or oil pump.
I am curious about the injectors. They read Open circuit on my multimeter on the ohm setting, however they must be working in order for the engine to run at all. I did wonder if it's possible for an injector to leak or be faulty in a way that more diesel than required is released into the cylinder. Therfore , excessive oil dilution. Perhaps an injector stuck open, if thats possible.
I'm sure some mechanic some where will have seen this issue before. I'd really appreciate help with it.