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The engine of concern is a 224cc CHP OHV small engine (Champion Generator), I can pull the rope and within a few pulls, the engine builds pressure that prevents me from being able to further rotate the engine. If you remove the spark plug and pull, then you can rotate it all day, no problems. This problem surfaced after I changed out the head\valve assembly for a brand new one, this job was accomplished without any need to go into the crankcase (the head was simply unbolted and refitted with a new one). I have been able to start this engine on the occasion that it could be started with one pull, after that it locks up tight under the compression. Similarly, if I just ease the rope out a few times slowly the same effect surfaces.

With the new head installed, I put the piston at the top and set the valve clearance. Is that all there is to it? Thanks for your time and consideration.

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Note that this answer is based on the original question, and it's less likely a solution given the new info provided in the question's edit. See comments below.

Sounds like your compression release is not working. When you worked on the engine, if you had the cam shaft out, you may have disturbed the compression release mechanism, which typically has a weight, a spring and a pin (or something) that raises one of the valves when the rpm is slow so you can easily rotate the engine for starting. As soon as the engine fires, rpm rises above that speed threshold and full compression is allowed.

It's also possible that the valve stem on the replacement part lacks the shape that allows the compression release to work.

See this other question / answer and search this site for "compression release" (using quotes) for more info.

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