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  #1  
Old 11-13-2018, 09:34 AM
PG13 PG13 is offline
 
Join Date: Apr 2017
Location: Fresno
Posts: 15
Default Air Cleaner Box (FAB) K&N Cracking and rubbing

I see a ton of posts on this and various fixes. I took off an old, and cracked FAB that had a metal plate on it with a huge gap between the filter and the housing, and built a new box and added support where the old one had cracked. Within 100 hours, it had completely eaten through the new bottom. My question is: Is there supposed to be ANY contact between the lower cowl and the air cleaner box via the baffle material? On BOTH assemblies, the thick plate that mounts to the performance airflow section of the throttle body has also cracked on the forward left bolt area. I obviously have something WAY wrong. I've only had the plane for a couple hundred hours. 815 hours on airframe. Whats the fix?

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  #2  
Old 11-13-2018, 07:38 PM
RV10Pilot RV10Pilot is offline
 
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Location: Medford, NJ USA
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The baffle material on the front of the fab should contact the lower cowl, but only the baffle material, there should be a gap that the baffle material seals.

I do recall that AFP increased the thickness of the mounting plate because of cracking in the past. Best bet is to contact AFP.

I also noticed from your photos that you have not complied with the "Auxiliary Airbox Retention SB" that can be found here https://airflowperformance.com/index.php/documents/
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  #3  
Old 11-13-2018, 08:52 PM
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AlexPeterson AlexPeterson is offline
 
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Location: Maple Grove, MN
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Top Plate:
I've made about 3 new top plates in 1600 hours (O-360, AFP injection). The first plate was the anodized plate from AFP. I don't recall how long that lasted, maybe 2-300 hours. (Side note: anodizing approximately halves the fatigue life of aluminum, all else being equal.) I made a replacement from the same thickness aluminum, but this time from sheet stock 2024. I also slightly offset the hole in the middle which attaches it to the servo, since a centered airbox seems to occasionally make contact with the left side of the cowl (mine's a 6A with the earlier cowls for which one needed to attach the scoop, so maybe I got it off center). The second plate probably went several hundred hours before cracking. The third one (and now fourth) I made from .062" 6061, not sure the material choice is any better/worse. I also made roughly rectangular "washers" to put under the bolt heads to better distribute the clamping force. The undersides of these are well filleted so that no sharp edge is in contact with the plate.

Another observation I made is that the large blue anodized fitting on the underside of the servo was making contact with the top plate, causing some cracks to initiate there. I fixed that by lowering the position of the clamp ring onto the servo by perhaps 1/16".

Fiberglass:
I laid new glass on the inside several times; it is simply a wear item I deal with. I put Kevlar on it the last time, which was only about 50 hours ago. I'll report observations at annual time in March.

Metal bottom:
I'm really against people doing this. Based on observing the wear of the filter on the bottom, I believe that the large pressure (suction) pulses resulting from each intake stroke are what causes the wear. I have to believe it could crack the bottom plate (if it's metal), and could cause a piece to be ingested in.

Airbox top:
I replaced a portion of mine somewhere in the 1000 hour plus range, as I saw some small cracks and because the alternate air door hinge was utterly worn out from vibration.

Drain hole:
It's a good idea to have a drain hole both inside and outside the filter, at the back (lowest spot).

Nothing else has been anywhere near as maintenance intensive as the airbox on my plane.

No perceptible vibration can be felt on the panel or anywhere reachable from the seat. (Yes, the prop is dynamically balanced.)
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  #4  
Old 11-13-2018, 10:13 PM
rockwoodrv9 rockwoodrv9 is offline
 
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Location: Meridian ID, Aspen CO
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Is there a concern that the fibers from the airbox can get into the engine? Pictures I have seen and a couple airboxes that had wear damage I looked at, most of the damage was on the outside bottom edge. As they wore out, it looked it was possible for fibers from the glass could get past the filter. Anyone with experience with this? I think I spent more time on the fab than the canopy and I am still not happy.
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  #5  
Old 11-13-2018, 11:21 PM
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petehowell petehowell is offline
 
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Location: MN
Posts: 2,175
Default O-320 seems better n=2

Rocky,

The design of the O-320 Airbox is different than the O-360 and mine with over 2000 hrs has not needed any maint at all. I have watched Alex repair his cracks, so have been looking on mine, but have not found any (yet). Our other hangarmate had on O-360 - 7A and had cracks in a few hundred hours, but then built an O-320 -9 and has over 500 with no cracks.

Since you are building the right plane, you might be just fine.

Nobody does better work or knows more about fatigue than Alex, so it is not a workmanship issue. I can assure you my build is of much lower quality than Alex's so that is not the issue.
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  #6  
Old 11-14-2018, 05:10 AM
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acam37 acam37 is offline
 
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This FAB is 100% fiberglass. I fabricated a new top piece and on the bottom where the air filter sits is a layer of core mat that is glassed over. This should be maintenance free for a long time. (Still havenít installed the baffle seal yet)
[IMG][/IMG]
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  #7  
Old 11-14-2018, 10:20 AM
PG13 PG13 is offline
 
Join Date: Apr 2017
Location: Fresno
Posts: 15
Default Phone with Performance Airflow vs Vans

So I talked to both companies about this. Airflow performance says we need a 3 inch gap between cowl and air box that is filled with baffle material so there can be a massive amount of flexibility between engine and cowl. Vans says 1/2". I had 1/2" with my new box. I think I'm going to experiment in the middle. Maybe start with an inch and cut from there.
Another suggestion from Vans was to wrap the air filter in plastic, line the bottom of the air box with ProSeal and squish the filter in place and let it dry. Then remove, and you'd have a custom mold that would prevent lateral rubbing. All good until the air filter shrinks. hehe.
I agree with the comment about hitting on the left side. I see more rubbing on the baffle on the left for sure. I suspect under load it moves there.
The ONLY thing that can break that upper mounting plate is excessive contact with the box and cowl according to Don at Performance Airflow. So.. more gap it is. I ordered a new plate from them. Vans suggested making one out of Stainless.
As far as the air filter rub is concerned, sounds like a lot of Pulse votes for the movement. I'm unsure. IF I can eliminate the box to cowl "contact" to take that out of the equation I'll be curious to see if that reduces the rubbing of the air filter. I really like the Kevlar thought too, but my air filter is CHEWED up! from the rubbing... so the ProSeal idea is intriguing.

Thanks for all the thoughts and suggestions! I think I'm ok with the safety wire holding on my bolts vs the bulletin. Have had zero issues.
Thumbs up to square washer idea. I'll do that when the new plate arrives.
I'm using the plane over 200 hours a year, so it's not taking long to see results of experiments.

Last edited by PG13 : 11-14-2018 at 10:47 AM.
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  #8  
Old 11-14-2018, 07:22 PM
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AlexPeterson AlexPeterson is offline
 
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Quote:
Originally Posted by PG13 View Post
So I talked to both companies about this. Airflow performance says we need a 3 inch gap between cowl and air box that is filled with baffle material so there can be a massive amount of flexibility between engine and cowl. Vans says 1/2". I had 1/2" with my new box. I think I'm going to experiment in the middle. Maybe start with an inch and cut from there.
Another suggestion from Vans was to wrap the air filter in plastic, line the bottom of the air box with ProSeal and squish the filter in place and let it dry. Then remove, and you'd have a custom mold that would prevent lateral rubbing. All good until the air filter shrinks. hehe.
I agree with the comment about hitting on the left side. I see more rubbing on the baffle on the left for sure. I suspect under load it moves there.
The ONLY thing that can break that upper mounting plate is excessive contact with the box and cowl according to Don at Performance Airflow. So.. more gap it is. I ordered a new plate from them. Vans suggested making one out of Stainless.
As far as the air filter rub is concerned, sounds like a lot of Pulse votes for the movement. I'm unsure. IF I can eliminate the box to cowl "contact" to take that out of the equation I'll be curious to see if that reduces the rubbing of the air filter. I really like the Kevlar thought too, but my air filter is CHEWED up! from the rubbing... so the ProSeal idea is intriguing.

Thanks for all the thoughts and suggestions! I think I'm ok with the safety wire holding on my bolts vs the bulletin. Have had zero issues.
Thumbs up to square washer idea. I'll do that when the new plate arrives.
I'm using the plane over 200 hours a year, so it's not taking long to see results of experiments.
Interesting... You might find some of the stuff the Sam James cowl guys use, the wet suit stuff or whatever, to bridge the gap from the inlet to the FAB. I may do that modification next annual...

Not sure I agree with AFP on the cowl connection being the only thing to cause cracks in the top plate. It doesn't explain the difference that we see anecdotally between 360's and 320's. The FAB are different designs, but both connect to the cowl the same and both have a top plate. It also doesn't explain the filter chewing. Movement related to contact with the cowl doesn't have enough cycles to generate the fatigue cracks that I've seen. It would mainly be startup/shutdown and moderate turbulence.

Keep in mind the purpose of the AFP bulletin is to safeguard against the large ring sliding off the bottom of the servo, not to keep the four bolts from loosening.

Re the pro-seal "mold", as long as it all is outside the filter, I might contemplate it. I'd not want any inside the filter that could crack off and go for a ride through the engine. Filter shrinkage as you note is a problem...
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  #9  
Old 11-14-2018, 09:09 PM
RV10Pilot RV10Pilot is offline
 
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Location: Medford, NJ USA
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Quote:
Originally Posted by AlexPeterson View Post
Keep in mind the purpose of the AFP bulletin is to safeguard against the large ring sliding off the bottom of the servo, not to keep the four bolts from loosening.
It is a service bulletin and we fly experimentals so you are not required to comply, but you may want to read this story http://www.vansairforce.com/communit...295#post868295
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  #10  
Old 11-16-2018, 10:46 AM
PG13 PG13 is offline
 
Join Date: Apr 2017
Location: Fresno
Posts: 15
Default I see!

Ok. Thanks guys, for keeping me straight on the "why" of the bulletin. Makes much more sense to do it!
Yeah, the ProSeal on the inside of the filter is a consideration. I also wonder about a filter retaining tab on the outside bottom, much like the outside top, to at least stop it in one direction of flexion. Might be better than the proseal.

Last edited by PG13 : 11-16-2018 at 10:49 AM.
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