Engine turns over but will not start

[Qwerty]

Just finished (trying) to completely overhaul an engine but I get this symptom when testing the car: "engine turns over but will not start". Initially I assumed I must have forgotten something so took the engine back out and basically rebuilt it from scratch (using the included manual) but end up with the same issue.
So to which parts can this issue actually be related to make looking for it easier? I would assume something's wrong with ignition or fuel but I'm actually pretty stuck at this point. Pretty thankful for any hints! Have fun!

[traublemaeker]

You're right on chasing spark, fuel, and aspiration for the big three most common issues. Low-effort diagnostics should occur before high-effort, so triple-check your engine externals first, because you will feel silly pulling the whole thing apart if you just needed new spark plugs.

Heads up, I'm not an expert, personally, but assuming plugs, wires, ignition, and fuel injectors are all good, my next steps would be to look at the things that tell the ECU that it's time to operate those:
-cam position sensor good, installed, and fully fastened,
-check the engine timing (while the crankshaft is in Top Dead Center as indicated by the notch on the timing gear, do the proper letters on the camshaft gears point toward the marks on the head?)
-Is the valvetrain assembled properly? (Lots of teeny tiny parts go into the cylinder head, and if they aren't all there the valves may not be moving properly)
-Is the car battery in good condition? (I don't know if the Catfish is rigged up this way, but while a starter motor typically stops first in low-voltage situations, it is theoretically possible for the voltage drop of cranking to prevent the ECU from operating)

I believe a turning-over/no-start situation is more likely to be caused by an issue in the top end than the bottom, so I'd work over the valvetrain next if you're not getting any luck with the externals. A bottom-end issue is possible, but I feel it would take a significant issue like all the piston rings missing for compression to be too low to start.

[Qwerty]

Thanks mate, it was an issue with crankshaft timing in my case. I just used the wrong reference points.
So in case anyone else is experiencing the same issue: carlsojos gave some great points where to start.
Some little helps for timing:
- Camshafts: Install the camlock tool and both pointers should be exactly one tooth below the lower end of the lock tool. E(xhaust) and I(ntake) should be aligned with the markers on the plate.
- Crankshaft: The little notch and the pin must be exactly at the upright position