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Snorkel rivet heads sucked into engine!?

Floog

Active Member
After removing the K & N air filter from the top of the snorkel I noticed several of the perimeter rivet heads that attach the baffle to the snorkel were missing.
This is an IO-360M1B standard build with 400 airframe hrs. I've replaced all of the perimeter rivets and washers with No6 screws and lock nuts. I'm thinking the rivet heads went right on through the throttle body and into the plenum. Maybe all the way through the exhaust, too? Just wondering if anyone else has seen this happen.
 
is this per the plans? best practice is not to use rivets downstream of the air filter for this reason.
 
Yup. Plans called out AK-42H rivets evenly spaced. Back-up washers on the outside of the snorkel, so only the rivet heads were ingested. Good point about not installing rivets there for that reason.
 
Yes, I had this happen to one of the rivets several years ago. And yes, it was built per the plans, using the correct rivets. I fully borescoped the engine, never found the head nor any apparent damage, so I assume it got sucked in, rattled around and eventually got blown out the exhaust.

I masked all the rivets and covered with a thin layer of fuel tank sealant to "capture" the heads more thoroughly, and haven't seen any issues since.

My guess is that the rubber face of the side of the filter vibrated against the rivet head, wearing it down and eventually what was left broke off. About gave me a heart attack when I found it, for sure.

https://vansairforce.net/community/showthread.php?t=168439
 
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If anyone else has seen this, perhaps Van's should be informed? If it's not extremely uncommon, maybe an SB is in order?
 
After removing the K & N air filter from the top of the snorkel I noticed several of the perimeter rivet heads that attach the baffle to the snorkel were missing.
This is an IO-360M1B standard build with 400 airframe hrs. I've replaced all of the perimeter rivets and washers with No6 screws and lock nuts. I'm thinking the rivet heads went right on through the throttle body and into the plenum. Maybe all the way through the exhaust, too? Just wondering if anyone else has seen this happen.

Years ago I experienced a 'burp' in the engine, had no idea what caused it as it never repeated it's self for the rest of the trip. Upon returning, the plane was took down for it's annual inspection & I found the bypass plate missing a couple rivets, same as you describe. I assume the rivet was sucked up & passed thru the engine, hence the 'burp'.
I decided to not replace the current (per plans) pop rivets that held the plate to the fiberglass, and instead made a .040 backing plate with #8 nutplates for inside the air filter housing. On the outside I drilled & dimpled the bypass plate for AN509-8 screws. Everything glued together with Proseal.
Turns out it was more than coincidence that I had to get a jug repaired on that engine 15 hrs later for a leaking exhaust valve, the shop saw evidence that something DID go thru the jug. If a CS4-4 pop rivet can do that to a valve, imagine what a broken #6 screw & lock nut can do.

Since then, I've copied this mod to probably 12 other different RV airboxes & have had no issues reported on any of those planes since.
 
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I covered the rivet heads in the snorkel with a couple of layers of fiberglass just in case.
 
Photos

Years ago I experienced a 'burp' in the engine, had no idea what caused it as it never repeated it's self for the rest of the trip. Upon returning, the plane was took down for it's annual inspection & I found the bypass plate missing a couple rivets, same as you describe. I assume the rivet was sucked up & passed thru the engine, hence the 'burp'.
I decided to not replace the current (per plans) pop rivets that held the plate to the fiberglass, and instead made a .040 backing plate with #8 nutplates for inside the air filter housing. On the outside I drilled & dimpled the bypass plate for AN509-8 screws. Everything glued together with Proseal.
Turns out it was more than coincidence that I had to get a jug repaired on that engine 15 hrs later for a leaking exhaust valve, the shop saw evidence that something DID go thru the jug. If a CS4-4 pop rivet can do that to a valve, imagine what a broken #6 screw & lock nut can do.

Since then, I've copied this mod to probably 12 other different RV airboxes & have had no issues reported on any of those planes since.

Any chance you could post photos?
 
Any chance you could post photos?
For me too, I don't even see where there is any pop rivet in the snorkel, especially that it says for the baffle.
The only possible place that I can see rivets are used on the snorkel is the alt air and that is typically used by a squeezed rivet. Anything else is on the outside of the snorkel and the filter should catch if it is going to fall off.

So, I am baffled
 
We, at least I am, talking about the alt air door. I choose to put a sturdy doubler plate inside the fiberglass air box & screwing the alt door plate together in a sturdy galvanized steel/fiberglass/aluminum sandwich structure. I don’t want any of my engines ingesting any more pop rivets.
 
For me too, I don't even see where there is any pop rivet in the snorkel, especially that it says for the baffle.
The only possible place that I can see rivets are used on the snorkel is the alt air and that is typically used by a squeezed rivet. Anything else is on the outside of the snorkel and the filter should catch if it is going to fall off.

So, I am baffled

I don't have the plans handy here at home, but yes, there are rivets that attach several pieces of aluminum angle to the snorkel to make the "box" frame that holds the filter and to attach the snorkel to the baffle.

I'll dig out the drawing when I'm at the hangar tomorrow...IIRC, it was a hand-drawn thing, not one of the OP series.
 
I don't have a finished picture, but these shows clecos where the pull rivets connect the filter bracket to the snorkel.
 

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First try at pix.
 

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I covered the rivet heads in the snorkel with a couple of layers of fiberglass just in case.

I work for a helicopter OEM and this is what we do for all fasteners in the intake.

We had a nut or screw go through a Rolls Royce 250 years ago thanks to a rushed mechanic. It wasn't pretty.
 
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