Lycoming SB388C Part 3 Alternate "Locally Manufactured" Tool

thingiverse

Human: The CAD version of the tool referenced in Part 3 of Lycoming Service Bulletin 388, Revision C, "Procedure to Determine Exhaust Valve and Guide Condition" is called out. The full text of the service bulletin can be found here: https://www.lycoming.com/sites/default/files/Procedure%20to%20Determine%20Exhaust%20Value%20and%20Guide%20Condition.pdf This example has been designed with a 5/8" rocker shaft boss directly, rather than using a 7/8 boss to press a rocker shaft bushing into. It also accommodates a dial indicator with a 3/8" shank. I have included the FreeCad .FCStd file and a .STEP file so that you can modify these parameters in either FreeCAD or your preferred CAD program. Being frugal, I am attempting this as a 3D Print in PLA. I will update this summary to inform the community of its success or failure. **Update January 14, 2020** After using this tool in real-world applications, I can confirm what most mechanics already know: that engineers often lack practical experience and have never actually attempted fitting part A into slot B in a real-life scenario. I have adjusted the overall thickness of the tool, the depth of the pocket on the front, relocated the two side set screw holes to bite further out, and modified the shape of the pocket on the front to accommodate larger angle valve engines. Additionally, I added a fillet to the back edge for improved clearance and counter-bored the body portion of the dial indicator clamping screw hole. I tried creating the stem extensions as shown in the SB according to their plans, but that part is not well-suited for printing in PLA. It would be more practical to fabricate that part from aluminum tube or machine it from bar stock. Fortunately, I have a young apprentice who was able to quickly produce this part on a lathe with ease, giving me zero notice. (Shout out to my boy Sean!)