Wobble test tool for IO-390?

Av8rRob

Well Known Member

• May 26, 2026

• #1

I am researching the wobble test for my -390 and trying to figure out the best tool solution for the bracket that holds the dial indicator. Does anyone have any great solutions/ schematics/ tried this with a 3-d printer ideas?

Thanks

 

jmra72a

Well Known Member

• May 26, 2026

• #2

I machined one. I simple found a mechanic that had a cylinder and then made a bracket to fit it. The Federal indicator was purchased from E-Bay for about $30.00. The drawing for the valve extension is available from a Lycoming service bulletin.

 

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Jetmart

Well Known Member

Friend

Patron

• May 27, 2026

• #3

I copied one from a pic I think I found on the site. Doesn't need to be fancy but the height of the gauge from the surface of the cylinder is important. That spec is in Lycomings service bulletin.

 

L

lr172

Legacy Member

• May 27, 2026

• #4

Jetmart said:

I copied one from a pic I think I found on the site. Doesn't need to be fancy but the height of the gauge from the surface of the cylinder is important. That spec is in Lycomings service bulletin.

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Glad you posted that. All of the go / no go dimensions provided are based upon the dial indicator height.