Rapco Spiral Wound Gasket Installation

[Brian]

I am reinstalling the OEM exhaust system on my 22/20-150 following the 100 Hr inspection with new Rapco Spiral Wound Gaskets. Two decisions aways come up.

1. Orientation of the gasket (higher raised side of V Gasket Up against Cyl or down against stack flange)

2. Best torque value for the 5/16 coarse nuts (want a good seal but don't want to bend/warp the flanges)

Lots of discussion on the torque value found across the web but not much consensus.

 

[SeanM]

https://www.lycoming.com/sites/default/files/attachments/Exhaust%20Flange%20Gaskets.pdf

pHave you seen this Lycoming bulletin?

 

[Gilbert Pierce]

Lycoming O-320 Overhaul Manual page 63, 5/16” nuts and cap screws 150”-lbs.

I have used this torque setting on the exhaust flanges for years with no issues as long as the studs are not corroded. If they are I replace them.

 

[Brian]

Thanks gentlemen for your input!

I did discover after I started this thread that Rapco does address the orientation question in a FAQ section of their web site. They basically say that orientation does not matter.

Makes me wonder why they manufacture these with the crush spiral material protruding more from one side than the other which leads to this confusion. I have historically installed these type gaskets with the more protruding side down and against the manifold stack flange, based mostly on the fact the flange is thinner and less likely to be perfectly flat than the mating surface on the cyl head.

For torque, the 150 inch lbs value Gilbert uses seems like a good middle ground. I don’t feel good at all about torquing these to 206 inch lbs like some have posted on this and other sites as that seems excessive to me.

Stripping out a stud and having to helicoil a low time cylinder is a big factor for me in deciding on a torque value for both these nuts as well as intake bolts.

I do fully believe in a follow up re-torque of these nuts after a few hours at flight operation, as they do loosen up with both heat and vibration.

Link to Rapco FAQ on orientation:

https://www.rapcoinc.com/FAQ.asp#gasketinstall