So I was almost convinced I had a valve showing signs of sticking that showed up on my trip home from Osh a few weeks ago.
I proceeded to educate myself on the Lycoming guidance around this subject and found out about SB 388C and the "Wobble Test".
Long story short, I did not have a sticky valve but I did go ahead and decide to follow the SB 388C and perform the wobble test on my exhaust valves.
I realized that the official Lycoming tools to perform this test were ridiculously expensive. I also found out that the Lycoming tool rental program is also pretty much a joke and there was no way I was laying out that kind of cash for that either.
So I decided to have the tool shown in SB 388C 3D printed out of glass filled nylon. Here is the result:
The parts came out looking great.
I used the tools tonight and I can tell you that the fixture to hold the dial indicator works great. The valve extension not so much (pretty much useless).
The design of the valve extension is very poor. I should not have followed the design as it is shown in SB 388C. There simply is not enough surface area actually clamping the valve stem for it to work well. Most examples I have seen where people have made this extension have not made them per the SB 388C. I threw the one I had printed in the toolbox and made another one out of a piece of CPVC, split with a band saw and clamped with a hose clamp. It worked great since it can grab more of the valve stem.
Then I found another design flaw with the tool described in SB 388C. The SB says "Tool must measure parallel to the rocker at the following height above the rocker box cover surface of the cylinder (machined O.D. surface of rocker box cover surface). Angle Valve Clearance – 0.750 ± .015 Parallel Valve Clearance – 1.190 ± .015"
Well the design for the tool provided in the SB 388C measures at 1.875" above the rocker box cover surface not 1.190".
Since this puts the measurement point at a larger radius from the center of the wobble of the valve in the guide, this makes any measurement taken using this tool larger than it would be if the measurement was taken at the recommended height above the rocker box cover surface.
I plan to account for the geometry differences to ensure I am in spec but this is pretty ridiculous on Lycoming's part....
Note: Unless you have the latest version of the Lycoming rocker arms, they are not interchangeable. Lycoming SI 1454A details how to ID them and where they go....