Do the cylinder head assemblies sold by Honda dealerships (e.g. 12100-P30-020) come complete with valves, springs, retainers, etc or are they bare requiring a machine shop to finish them before installation?

 

To the best of knowledge to come complete. But you would not have to have a machine shop assemble a fresh new head. Being all the tolerances are perfect due to them being new and never heated to the point to change anything from the finish machining that they receive from the factory

 

That would be up to you IMO, you can buy them bare or fully assembled from my understanding of their catalogs.