Wobble Test Fixture for SB 388C: angle or parallel valve cyl

[Dave Clark]

This is my improved version of the Wobble Test Fixture described in Lycoming's Mandatory Service Bulletin 388C. When I first made the fixture depicted in the engineering drawing in the Service Bulletin, I found that on the angle valve cylinders in my shop, if I clamped the fixture to the inboard rocker shaft boss, the dial indicator tip would not reach the split gage. Therefore I added approximately 3/16 inch to the length of the fixture. (Note: split gage is spelled correctly and not to be confused with the gauge in a dial indicator.

I also designed and fabricated a centering tool which is basically an aluminum dowel with a cove milled into the end. The radius of this cove is identical the radius of the OD of the split gage (exhaust valve extension). By placing the centering device into the bore normally occupied by the dial indicator gauge, and then pressing it firmly against the split gage, it ensures that the dial indicator tip will be perpendicular to exhaust valve.

While I have designed (and sell) a much simpler fixture for use on just parallel valve cylinders (see separate ad), the device described herein will work with either an angle valve OR a parallel valve cylinder. If you will be performing the wobble test on both types of cylinders or just angle valve cylinders alone, then this is the test fixture that you need. If you are performing the test only on parallel valve cylinders, then you will want the simple parallel valve fixture.

Included with the Test Fixture: Dial Indicator Gauge, Centering Tool, and Written Instructions

See my video tutorial on YouTube at: https://www.youtube.com/watch?v=bq9YVsepphs

Price: $250
S&H: $10

Contact:
Dave Clark
dave520@prodigy.net