So I have been driving myself crazy looking at head options. Jim at JDM and Ron at Foxlake both very helpful, but with different perspectives. Found this while researching, and I wonder, is this why some have success with bronze valve guides and some do not have success????
http://www.enginebuildermag.com/2010/10/sizing-up-the-valve-guide/
What about finish?
Ra finish is all over the board as I found during research for this article. Most agree that too rough will reduce life and too smooth will not allow enough oil to be held in the bore to provide the necessary lubricant and heat transfer. My research has found that somewhere between 30 Ra and 80 Ra is the range. Bronze is suggested to be a lesser or smoother Ra especially for high-performance and cast iron tends to be higher on the scale especially for diesel as this rougher Ra will hold that much needed oil for diesel lubrication and heat transfer.
Most reamers except the carbide reamers will not deliver the necessary Ra finish you need for these newer valve guide applications. The diamond hones and diamond reamers will deliver the finish, as will abrasive type of guide hones, but the regular reamers need a little help with another tool after the valve guides are to size. Using a small diameter flexible honing tool will get you a couple more positive Ra’s and then follow through with an honing tool designed for finish or plateau honing. Yes these soft honing mandrels are made out the same material you use for final cylinder hone finishing. My testing showed with the combination of hones delivered a finish in the single digits. Again the Ra finish is directly related to the application. Always check with your valve guide supplier to determine what Ra you need for that application.
