Same layout as the 520, and 510 before it.
Metal case, that holds the engine assembly.
And as before, no one can provide any proof that the clamshell design, with the seals and bearings encased in the all metal block, that is bolted to the metal case, is in any way shape or form BAD. It simplifies the saws design and assembly, and makes any repairs less invasive and time consuming. When a bearing goes out in a 440, how long does it take you to replace BOTH crank bearings and BOTH crank seals and produce a running saw? What special costly tools are required? With the Echo method you simply unbolt the carb and muffler, remove the flywheel...remove the cylinder screws, and lift out the engine. Remove the case shell, remove the bearings and seals, slide on new bearings and seals, put the cap on, and drop it all back in...
If a bearings fails catastrophically, and eats into the case...on a STIHL, you are SOL. However on an Echo, you need only replace the cylidner and shell.
Keep in mind here that the acclaimed Husky 350 isnt nearly as robust as the Echo design, With Husky simply mounting the metal jug to the plastic case, with the seals and bearings mounted to the plastic case, and Ive never heard of any problems with even THAT deisign with regular use.
Im just saying, you may not like they way ECHO does it...but you cant prove it is inferior to the way Stihl does it, you can only offer opinion.