Hi,
The engine has no compression. Either timing is off, valves are stuck open, the spark plugs are removed, or the new cylinder head is completely bad. Just listening to it, there isn't any compression. It will never start. I did hear the backfire in the first video. Likely, there is a build-up of unburned fuel in the cylinders which eventually ignite.
If you can and want confirmation, I would recommend performing a compression test on the engine. I can't imagine you will find more than 20 psi in each cylinder. Here is a link that shows how it's done:
https://www.2carpros.com/articles/how-to-test-engine-compression
Here is the really bad news. All Honda engines are interference engines other than a couple of their V6 engines. What that means is this. If the timing is off, there isn't enough room/clearance between the tops of the pistons and an open valve. As a result, they hit and cause internal damage.
So, I need to know if the timing marks were exactly as they are indicated in the directions I provided. (Camshaft and crankshaft)
Let me know.
Joe
Sunday, December 26th, 2021 AT 8:21 PM