74A1 questions

Definitely is a D333T engine (4-1/2" bore). Valve guides are #5M8023 until you get to s/n 74A2467-up where they change to #5S4507. Early guides are flanged. Replaced by 4N3668 ( no flange)

I would replace the thermostat, I also think maybe engine has been idled a lot and or the wrong type of oil been used.

It's a slippery slope that leads to a complete overhaul at the bottom, but I would be going to some effort to assess the cylinder/ring wear while the head is off. Unless someone replaced the liners, pistons etc and ignored the head completely, the engine is very likely in need of an overhaul. I have a complete set of STANDARD main and rod bearings I would like to get rid of if you find your crankshaft is not worn enough to justify a regrind.

OK. further info, and thanks all for the responses.

Oil pressure is good and pressure comes up as soon as you crank the engine, before it even fires.
There is no blowby to see at high idle.
Where did the crud come from, could be the egg shaped guide. Or, as I know too little of the history, it could have had a bad injector-- there is a reason he suddenly changed them all and did the pump when the engine quit. I think if it was burning oil in that quantity there should be some panting out the breather.

I will be replacing the thermostat, it looks like there are signs of cold running. Bores are shiny with no wear ridge to be felt.
Nozzle Tips should be 8N4694, but it has 8N5986 in it. I don't know what effect this would have.
Have included pictures of the engine plate, and I don't know if there are any numbers that should come after the Series C or not.

Worn valve guides can let a large volume of oil past, and this ends up as coked oil (my term) choking up intake and exhaust manifolds. I just cleaned out my D2 5U's exhaust manifold. #4 had only a finger-size opening left in it before I cleaned it - #1 wasn't much better. Did the exact same thing on my wife's Audi except on that engine, it was the intake manifold that was choked. I'd guess that a lot of burned oil gets wrongly attributed to piston rings when it may have been the guides. Good thing about doing guides is that it's easy, cheapish, and also can improve your compression pressures if the valves weren't seating properly.

On your injectors....
74A1 to 1574 originally used 180 deg. counter bored nozzles Valve Service Group #3S6638 which contained #2S4442 nozzles.
74A1575-up originally used 90 deg. counter bored nozzles Valve Service Group #8M1584 which contained #5M4086 nozzles.
There seems to be a lot of confusion out there on whether nozzles are referred to by their correct part number or Valve Service Group part number. What reference I have may indicate your 8N5986 is a 2S4442 equivalent but I am not 100% sure. The 8N4694 does not appear to be a candidate.

On your injectors....
74A1 to 1574 originally used 180 deg. counter bored nozzles Valve Service Group #3S6638 which contained #2S4442 nozzles.
74A1575-up originally used 90 deg. counter bored nozzles Valve Service Group #8M1584 which contained #5M4086 nozzles.
There seems to be a lot of confusion out there on whether nozzles are referred to by their correct part number or Valve Service Group part number. What reference I have may indicate your 8N5986 is a 2S4442 equivalent but I am not 100% sure. The 8N4694 does not appear to be a candidate.

[quote="Old Magnet"]On your injectors....
74A1 to 1574 originally used 180 deg. counter bored nozzles Valve Service Group #3S6638 which contained #2S4442 nozzles.
74A1575-up originally used 90 deg. counter bored nozzles Valve Service Group #8M1584 which contained #5M4086 nozzles.
There seems to be a lot of confusion out there on whether nozzles are referred to by their correct part number or Valve Service Group part number. What reference I have may indicate your 8N5986 is a 2S4442 equivalent but I am not 100% sure. The 8N4694 does not appear to be a candidate.[/quote]

Old Magnet, you seem to have a bible with all the old numbers.
Wondering where to download a PDF parts manual for this critter. I see Cat sells chinese parts as Cat Classic but the numbers are different and they do have a cross catalog to download, but you need a original number to start with.