Hi Dave, You probably don't remember me but I wrote you a thank you note last year for your website because of all the great info and it tipped me off to a problem I now seem to have like you did. I have two atkins 13b's from the batch you got also. I have taken fastidious care of them, fogged them every three years and such, but no one before you mentioned anything about the cooling.  I talked to Atkins, both Dave and Dan, and they said tear down if the passages are pitted.  I inspected several passages, and yes there was a a little  "hanging, granular" rust, but no pitting that I could see. I assumed my dry climate here helped.  One engine is fairly clear and one engine will not allow 35 psi air ( the amount specified for the test by atkins) to pass from the block drain to anywhere up. indicating a passage  block. Do you have any advice ? I would really appreciate it.I think if worse comes to worse I could remove the freeze out plugs and all cooling ports and clean it that way until it runs clear, but hopefully there is something easier. I really don't want to tear these down and send them off to overhaul, but yet I will do what I have to do before putting them in my airplane.  I'm forwarding a screen shot of our solid works drawing we are using for CNC parts manufacture and stress analysis.  It's actually very simple and We think very cool.

Thanks again,

Lionel