I was recently conducting an inspection on my 9A (IO-320) and found the alternate air door mechanism ( bottom of the air box) hanging off. There were three screws that hold the flange to the box missing. What are the chances these screws were sucked up into the engine or fell to the ground? What suggestions does anyone have and how should I proceed?
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Missing Alternate Air Door Screws
- Thread starter Kuperman
- Start date
I lost a screw from my airbox and it was sucked up into a cylinder smashed a sparkplug ground strap tight. But then it found its way back to the intake manifold and went to a different cylinder and smashed a different sparkplug grounding strap. I found it when I removed a intake tube and it was just sitting there.
I remember this happening to a guy a couple of years ago. They symptoms he had were cylinder misfires because the ends of the spark plugs were squashed. The amazing thing was that a screw with a fiber lock nut still on it got sucked into a cylinder, beat the crap out of a spark plug, fell back out through the same intake valve and got sucked into a second cylinder where it did the same to that one, then fell back out of THAT intake valve. I wouldn't have thought that was possible, but it's hard to argue with when you read through the thread I linked. He eventually found the hardware laying in an intake runner. As I recall, his compressions were good, so the valves didn't get too beat up, which is also surprising to me.
Pulling the plugs and borescoping everything would seem like. a logical next step.
Multiple Spark plugs damaged
I have about 400 hours on a completely rebuilt O-320-D2A that has had something crush the grounding strap closed on three different spark plugs in the last 3-4 hours.NGK-BR8ES first 2 times running with 2 Emags. This has happen on two different cylinders both the back cylinders 3 once & 4...
vansairforce.net
Pulling the plugs and borescoping everything would seem like. a logical next step.
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I had the same thing happen - but if the builder followed the plans, it was held by blind rivets, not screws, and they tend to pull through the fiberglass. I repaired mine, but glassed an aluminum flange to the inside of the air box so the rivets wouldn’t pull through again. And I borescoped the cylinders just to be sure. Pics before - during - after repair. PDF of relevant plans attached, too.
Attachments
I make an .025 Alum sheet that goes on the bottom of the box. It gives another metal surface for the rivet to hold on and also prevents the FG from wearing away from filter movement. Very easy to do this and works well.
I've had so many different failures with this poorly designed system, I finally removed it and glassed it over. Sure, there is some risk with this, but after two failures in quick succession, I decided the risk of leaving it in place was more than the risk of removal. To each his own.
Stephen
Stephen
Is it possible, the screw is still laying at the bottom of the snorkel? I would run a borescope in and look.
As far as the alt air door, you may want to read some of the threads here. Some builders leave it off since there is little chance for icing or blockage. If you replace it, use blind rivets and proseal the hardware inside.
As far as the alt air door, you may want to read some of the threads here. Some builders leave it off since there is little chance for icing or blockage. If you replace it, use blind rivets and proseal the hardware inside.
This issue has come up repeatedly on VAF
A few planes came into my hangar for inspection with loose or missing hinge screws, my solution is to drill that screw head for safety wire.
As for that base plate fastened with glue & pop rivets (per plans) - this cost me 2 cylinders on my personal plane. My solution is to replace all pop rivets with AN507-8R8 screws (add a couple extra for good measure), nutplates solid riveted to a .032 aluminum ring inside the housing, all pro sealed together.
I’ve done this to multiple other RVs over the years. No further issues after these fixes & who knows how many thousands of bucks I’ve saved those owners…
A few planes came into my hangar for inspection with loose or missing hinge screws, my solution is to drill that screw head for safety wire.
As for that base plate fastened with glue & pop rivets (per plans) - this cost me 2 cylinders on my personal plane. My solution is to replace all pop rivets with AN507-8R8 screws (add a couple extra for good measure), nutplates solid riveted to a .032 aluminum ring inside the housing, all pro sealed together.
I’ve done this to multiple other RVs over the years. No further issues after these fixes & who knows how many thousands of bucks I’ve saved those owners…
Yes, I’m definitely going to do something different with the fix. Im also concerned about where the missing hardware has gone.
