Exhaust system mounting nuts

We bought a brand-new IO-540 crate motor. The exhaust ports had plastic covers on them mounted with standard steel nuts, but also within the engine packaging was a set of twelve aluminum locknuts. These locknuts fit on the exhaust mount studs and there's exactly enough of them, but I'm not positive that's where they go. There doesn't seem to be any instructions either way.

So - which nuts are used to mount the exhaust system? Do I use the standard steel nuts, steel nuts with lockwasher, or these aluminum nuts?

Is it possible that those aluminium nuts are stainless steel? If so then they are the ones to use.

silver plated

My guess is they are not aluminum. My guess is they are silver plated. For the O-360 the correct nut is the STD2233 which is a silver plated stainless steel nut.

I am sure the 12 nuts are silver coated superalloy for the exhaust flanges. My friend scoped this out. Note they are about $25 each, so be proud you have them. I don't know why they are recommended for the 540 but not the 360.

Here is what the Lycoming guy sent him:

"The 12ea Self Locking Nuts (STD-2043) and Plain Washers (STD-35) should be used, along with the 6ea exhaust gaskets (77611) that also shipped loose, when you install your exhaust system.

The 4ea Plain Washers (STD-35), Lock Washers (STD-475) and Nuts (STD-1410) should be used in conjunction with the fuel servo spacer (73966) and gaskets (66224 & 77504) when you install the fuel servo to engine sump."

If you don't want the STD-2043 nuts I will send my address via PM.

krwalsh said:

My guess is they are not aluminum. My guess is they are silver plated. For the O-360 the correct nut is the STD2233 which is a silver plated stainless steel nut.

Click to expand...

Not always... my O-360 Tiger calls out STD-1410 nuts which are just plain nuts, and cheap...

http://www.aircraft-specialties.com/nut-exhaust-manifold-nut-5-16-100-per-pack-std-1410-ms35690-502/

Though the exhaust system is airframe specific, the Grumman parts manual states that exhaust nuts are supplied with the engine.

The Lycoming O-360-A1A wide flange latest parts manual (and even the TIO-360) also calls out the STD-1410 nuts.