Help with an arrangement

After a complicated repair (the timing chain tensioner broke and ruined the entire timing belt kit, including the housing, and damaged the exhaust valves; it's all fixed now and several parts were replaced), I started my Nissan D21 pickup truck. It started normally, with a little rattling and all that, then I turned it off. Later, I tried to start it again and it wouldn't start. Why is that? I'm desperate and the mechanics can't figure it out.

Check if it's spark or fuel that's preventing it from starting, that way we can guide you on where to check.

There's spark, fuel, and everything...
New details: In the morning, it starts normally (I put in new spark plugs). I run it for as long as I want—5 ​​minutes, 30 minutes, an hour—but after turning it off, when I try to start it again, it won't start. I tried something I saw someone do once: I disconnected the injector connections and tried to start it, and it started briefly. Then I connected injectors 1 and 3, and it started perfectly, with a little knocking. Next, I connected injectors 2 and 4, it stabilized, and I took it for a spin, and it worked perfectly. I turned it off again, let it rest for a while, and it wouldn't start again. I tried the previous method again, but it didn't work. It only drained the battery from all the attempts... I don't know what else I can do.

If you change the exhaust and intake valves and it has starting problems, do this:

1- Check the valve clearances. D21 is 8mm for intake and 10mm for exhaust.

2- Check the engine compression with a gauge.

Greetings from Costa Rica.