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The Amazing Shrinking Air Filters

Walt

Well Known Member
I find this all the time...

Wrong:
RV%2520air%2520filter%2520001.jpg


Right:
RV%2520air%2520filter%2520003.jpg


The E3450 you get from Van's is not the same as the E3450 from Spruce or other sources, the smaller ones lack the 'B" suffix seen here:
RV%2520air%2520filter%2520007.jpg


I've not found another source other than Van's for the correct filter.
 
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That's my point, the A077A6 is not the same as the A077A6-B but both are listed under the same E3450 PN.
 
The K&N filters are known to shrink over time, whether from heat or some other reason. How old/ how many hours on the one in the first pic?

I've bought E-3450 from Autozone and it's the same as the one from Vans. Same K&N part #, stands to reason it's the same unit.
 
I guess I'll just have to go buy one at AZ and then compare it to the ones I get from Van's.

I've seen this at least half dozen times, perhaps they all shrunk exactly the same amount :confused:
 
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Are you saying you've never seen these filters shrink over time? Also, I'm still curious how many hours were on the smaller one. We could be talking about two completely separate issues here.
 
The K&N filters are known to shrink over time, whether from heat or some other reason. How old/ how many hours on the one in the first pic?

I've bought E-3450 from Autozone and it's the same as the one from Vans. Same K&N part #, stands to reason it's the same unit.

Same here.
 
Same here.

+3 I just bought one for my recent condition inspection (240 hrs). Amazon ($32 IIRC) and it fit perfectly (E-3450). Yes, I cleaned the old one last year per K&N but didn't want to mess with it this year. The new ones come oiled and ready to go.

Walt,
do you have any connections at K&N so that you could check with them and settle this once and for all and have it made into an VAF engine sticky. Comes up all the time. Especially, when well respected AP guys, like yourself, have issues with the E-3450.

As and additional note, I read somewhere (probably here on VAF) that K&N was contacted and stated that the mold had not changed and the "Oil before Use" caution on the molded part was outdated. They come pre-oil'd.
 
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They do indeed shrink. I believe I'm on my 3rd filter in 12 years. The latest one doesn't seem to be shrinking as much, but the first two looked like the OP pic after about 4 or 5 years.
 
Ok maybe they do shrink that much over time, I know they shrink a little when you wash them but I had no idea they would shrink this much!

This particular aircraft only has about 450 hrs on it and is about 5 yrs old.

Maybe someone can post the ID/OD of the replacement filter they bought (with no 'B' suffix) and I'll get the same on the new Van's filter.
 
Maybe someone can post the ID/OD of the replacement filter they bought (with no 'B' suffix) and I'll get the same on the new Van's filter.


Part E-3450 Product Specifications
Product Style: Round Air Filter
Height: 2.5 in (64 mm)
Inner Wire: No
Inside Diameter: 6.25 in (159 mm)
Outside Diameter: 7.75 in (197 mm)
Top Style: Open
Top Material/Finish: None
Air Filter Shape: Round
Filter Material: Cotton Gauze
Flanges: None
Package Contents: 1 Air Filter
Package Quantity: 1
Filter Re-Oiling Amount: 0.65 oz (19 ml)
Weight: 1 lb (0.5 kg)
Product Box Length: 8.5 in (216 mm)
Product Box Width: 3.63 in (92 mm)
Product Box Height: 8.63 in (219 mm)
 
I had one shrink and over the course of the 300 hrs this year, the relative movement had worn a hole in the bottom of the filtered air box.
Re glassed with 4 layers of cloth.
 
Well looks like you guys are right, the filter I removed is a full inch less in ID/OD measurements than the figures posted above by Brantel which matches with the filters I get from Van's.

I am amazed it could shrink that much!

So I guess the title should be changed to "The Amazing Shrinking Air Filters".
 
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Get them replaced

K&N will replace filters that shrank under their 'million mile warranty'. I've had a few replaced.
 
K&N Engineering Contact Info

Perhaps a call to them is in order. They have been pretty responsive to serious technical inquires in the past.


Send all product related inquiries to: [email protected] If your question is vehicle specific, please provide the vehicle's year, make, model, and engine size in your email.

Phone: (800) 858-3333 or (951) 826-4000

Mailing Address:
K&N Engineering, Inc.
PO Box 1329
Riverside, California 92502

Physical Address:
K&N Engineering, Inc.
1455 Citrus St.
Riverside, California 92507
 
The air filters made of cotton shrink just like our clothing, especially when exposed to thermal cycles, 100LL and engine oil...oil draining down intake tubes and over priming.

This particular filter is undersized for the air volume passing through it for any of our engines of 360 cu in or greater turning 2700 rpm. Add to this the ram effect at 160-180 kias and it is easy to see why they shrink.

K&N does not warranty filters used for off road use.

I bonded a .032" aluminum plate to the fiberglass bottom to prevent the filter from wearing through and to provide better attachment for the alternate air door.
 
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Another data point to all the data points...

I'm coming up on 400 hours and my filter has been filtering since March 2008. It's probably starting to get close to the picture that Walt posted at the very top. I need to think about getting a new one as well. Funny how these things shrink and thanks for the explanation why, guys.

So, there's another data point about the ever shrinking K&Ns filter.
 
This thread got me looking at my air filter while I have the plane apart. Almost 400 hours and 7 years old...don't think it's ever been replaced or cleaned but I'm not certain of that since I bought the plane flying. I looked on amazon and got a replacement E3450 after some automatic discounts when I went to checkout for $12 (only 7 left at that price). Can't beat that...hope it fits and hope others can benefit from that. Only one worked with the discount...I couldn't get more than 1 at that price.
 
So please help me

I received my FF kit.
Nowhere does the part# E-3450 appear on the filter, only on inventory list. It was sealed in a plastic bag, no box. No VANS or K+N number on the bag.
On one side it says A077A6-T, on the other side it says A077A6-B.
The measurements are as supplied in Brantel's post.
It is round and not oblong as shown in the plans. What keeps it in oblong shape inside the FAB. (I have not build the FAB yet, but could not find the answer to this in the description).
Printing on the filter also says "oil before using". Is it OK to use as implied in this thread? Is there a way that I can tell if it was indeed oiled? It has pink/purplish color to the element.
Thank you.
Johan
 
When you build the FAB there are tabs that hold the filter in place. These tabs will make the filter form an oval. The filters come pre-oiled now (the red color on the filter) so no need to add anything except during future maintenance.
 
My last filter bought in 7/2012 already looks exactly like that in the OP. It has shrunk about 1.5 to 2 inches in only 1.5 years. I can't imagine keeping the filter on for 4 to 5 years. It would probably look like a donut.

Instead of ordering the filter from Van's, i think i will order it from the local autoparts store for $10 or $15 more. Then in a year from now, i will try and swap for a new filter under warranty with the original sales receipt.

Just found out the local autoparts stores dont carry it in stock. There goes that idea. argh!

Jae
 
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Because of this post I've kept an eye on my filter, here it is after 31 hours on the tach. I really can't believe it shrunk that much, you can see the sharpie marks of the original diameter on the FAB.
544B466F-3A00-4F36-BE93-F36B1074571F_zpspsixzasn.jpg

3F6FAE55-84DA-429E-8867-D0BAD19E073E_zpsmoqwvcmi.jpg


A phone call to K&N followed by an email with pics and a description of purchase date, time in use etc netted me a new filter in the mail.

I'm curious if it's the filter or the installation/Fab that is making it shrink.
 
Because of this post I've kept an eye on my filter, here it is after 31 hours on the tach. I'm curious if it's the filter or the installation/Fab that is making it shrink.

Did you install FAB drain tube?

I am wondering if those like me that installed the aluminum piece on the inside, which causes a little more clamping force on filter are having this problem?

Also what are your normal cruise altitudes? This filter is marginally sized for a 360 cu in at 2700 rpm, let alone my 540. If you fly low/high MP/high RPM a lot, you might be creating a higher pressure differential. I rarely fly low and rarely at high power settings due to birds(live and man-made).

Mine is exactly the same size after 135 hrs 2.5 yrs.
 
Today I replaced air filter with new after almost 1,300 hours. It deteriorated a bit during three years in service. It was cleaned and recharged at every condition inspection.






It held the same shape.







But it chewed a hole in the bottom of FAB which was promptly fiberglassed. :)




 
I'm curious, the folks that have had sever shrinkage :D (that's just funny) . . . I mean on your filter, do you fly in a lot of rain?
 
Did you install FAB drain tube?

I am wondering if those like me that installed the aluminum piece on the inside, which causes a little more clamping force on filter are having this problem?

Also what are your normal cruise altitudes? This filter is marginally sized for a 360 cu in at 2700 rpm, let alone my 540. If you fly low/high MP/high RPM a lot, you might be creating a higher pressure differential. I rarely fly low and rarely at high power settings due to birds(live and man-made).

Mine is exactly the same size after 135 hrs 2.5 yrs.

I missed this question several months ago, yes i did install the little aluminum angles but I don't believe they clamp. I might have introduced more clamping force than the average builder between the carb/FAB plate and the FAB, not sure. When I attach the airbox the airfilter is scrunched approximately 1/8 inch when tightened.
My first 30ish hours were breakin fly it like you stole it at mostly lower altitudes (below 6000) and winter temps 10-50*F. That being said I am fixed pitch and it limits my RPM until I get the speed up.
My next 30ish hours have spent a good deal of time around 60% LOP above 6000, I noticed at my last oil change the new filter is shrinking but not as bad.
5EC49DAF-B805-485E-8FD4-4EC7EE22163F_zpscl4fe3p5.jpg


Maybe I'm doing something wrong reference Vlad's filter...
 
Replaced the K&N E-3450 air filter in my RV6 yesterday. Shrinkage of the old filter was as seen in previous posts in this thread. New filter outer circumference was 24.625 inches and fit perfectly within the tabs on the air box. Old filter had shrunk to 23 inches outer circumference or about 6.6%.

Van's price is $47 (plus shipping). I got the filter from Amazon for $38.99 with free shipping due to prime membership.

Never flown in the rain per question above.
 
Shrinking

I have a K&N round filter in my BMW motorcycle . I removed it for cleaning and it shrunk enough that it would not fit back in . I contacted K&N , gave them the model # , year purchased and mile age , they sent me a new one .
They honored their Million Mile Warrantee .
 
The E-3260 in my O-320 RV6 is 12 years old now and has finally shrunk enough that it's no longer fitting well. I just ordered a new one from Spruce for $8 cheaper than Vans. I guess I'm about to find out if if fits :D
 
I think part of the contributing factor beside heat is the cotton fibers the filter media contain shrink after water exposure.
 
Posting a reminder to everyone doing their CI's to check the air filter for shrikage. The old filter had just shy of 1000hrs and 8 years on it and probably should have been replaced earlier. It was no longer sealing properly inside the airbox. The new one was soft and easily bendable whereas the old one was rock hard. In my opinion everyone should have this listed as a consumable on their Condition Inspection check list. It is obvious from the pictures which is the new one and the old one so no captions necessary.

20151020_182927.jpg


20151020_182914.jpg


20151020_183101.jpg


20151020_183016.jpg
 
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I installed a K&N 3322 two months ago as part of an FAB and scoop inlet overhaul, no modification of the filter required to mate the carb side, but I did make a more appropriate bottom plate. It is working well after 15 hours. I am pretty sure I picked up 3 or 4 knots on the top end. :rolleyes:
 
K&N filter warranty policys excludes almost everything

Guys,
Second shrinking filter. Did a chat online. Be warned, unless the filter is being used in a car, on a paved road there is no warranty (paraphrased).
Any 'custom vehicle' or 'off road' use is not covered per a somewhat curt web chat before they simply disconnected me(and no I was not being rude). A complete 180 from my first conversation with them two years ago.

It was time to update the FAB anyway. Outside of James aircraft, anyone have another basic FAB they have been modifying for a RV7 vertical induction?

*I think James stuff is very well done but they have been too busy with other projects to work on this.....
 
filter shrank - in three hours

I had 25H TT on my filter before needing to do my condition inspection. I removed the filter which fit just fine, it did not snap off or anything odd. It sat for a couple hours, still fine. I washed it (K&N filter wash) , set it out to dry (breezy sunny day after a gentle air blow off). Was wrapping up and pulling stuff in to find one side of the filter had shrunk significantly, diametrically, over three hours of drying time. It looks like a trunchated cone now. I can't say if just letting it sit would have caused the same shrinkage, but I'm suspicious of the washing process. I'll go to blow-off/shop vac/re-oil for regular condition inspections now, and a periodic replacement (3 years? 5? Depends on degradation or deformation) rather than washing.
 
I had 25H TT on my filter before needing to do my condition inspection. I removed the filter which fit just fine, it did not snap off or anything odd. It sat for a couple hours, still fine. I washed it (K&N filter wash) , set it out to dry (breezy sunny day after a gentle air blow off). Was wrapping up and pulling stuff in to find one side of the filter had shrunk significantly, diametrically, over three hours of drying time. It looks like a trunchated cone now. I can't say if just letting it sit would have caused the same shrinkage, but I'm suspicious of the washing process. I'll go to blow-off/shop vac/re-oil for regular condition inspections now, and a periodic replacement (3 years? 5? Depends on degradation or deformation) rather than washing.

The certified K&N filters are sold as Challenger products. This is a link to their cleaning instructions. No mention of blow drying -

http://www.challengeraviation.com/Illustrated Air Filter Instructions.pdf

The Challenger filter for my Tiger has the original K&N part number on it - 60's era Dodge slant 6 I believe - and an extra stamp of "FAA-PMA" on the rim. :)
 
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set it out to dry (breezy sunny day after a gentle air blow off).

The K&N cleaning instructions say "After rinsing your filter, gently shake off the excess water and only allow filter to dry naturally. Do not apply oil until the air filter is completely dry."

I admit that "dry naturally" can have many different meanings (the sun and wind are natural), but my interpretation has always been to do nothing to artificially accelerate the drying process.
The filter media is cotton. It will shrink just like a 100% cotton shirt will.
If you do anything to accelerate the drying process, it will shrink that much more.
I always do the cleaning immediately after removal and then set it aside on my work cart to let it air dry over night. They can be reinstalled immediately after being oiled.
 
I bought a new filter at the first CI. I then cleaned the old filter and let dry as Scott suggests, in the hangar in free air. When dry, after a couple days, I put it back in the box until next year. I then oil the spare and install it (if it is new it is pre-oiled). At the next CI, repeat.
My two filters have lasted 750 hours total and more than ten years with no shrinkage..
 
Blow off as root cause?

So the feedback is blow drying is somehow the cause of the shrinkage. I understand the cotton consideration. The shrinkage is diametrical, not in height, and only on one side. I've not been able make these elements come together with blow drying as a contributor. I'm suspect of the washing solution as a contributor for the same reason now too. A lunchtime Ishikawa diagram, maybe, get everything on paper. I'll report back after I deconstruct it, maybe the rubber returns when free of the cotton. I'm curious about the durometer, and if there's a difference top to bottom. If nothing else, it's an excuse to goof off in the materials lab at work.
 
I think I have the same issue with the K&N in my O-320 powered RV6.

I bought the plane as a flying beastie about 10 years ago with what I believe is probably its original filter.

Not having realised the saga of the shrinking air filters I have just been popping it off, cleaning and re-oiling it once a year. I always wondered about needing to loop some locking wire around the last bolt and give it a heave to get it to locate into the hole in the bottom plate. Thought that was just the way it was.
The cutaway is an odd feature so why not this?

"Bottom plate" I hear some of you say?
My RV was finished in 1994 so has lots of early features - floor mounted pedals etc. - and one of these 'features' seems to be that the FAB sits around the filter but doesn't actually retain it. The filter is clamped between the top plate and a bottom aluminium plate by 4 long AN3 bolts. The fibreglass plenum (with hot air door etc) is then fitted around it and attached to the top plate.
This may, of course, be a modification the original builder added, but it does mean that one can see the filter is (very!) snugly located on the carb inlet before covering it all up with the plenum box.

A friend gave me a secondhand RV6 filter a while ago, and mine is appreciably smaller than that one. As the 'new' one was in a box I was able see the K&N part number was E-3260 - and then found it on the Van's site anyway - and have ordered a new one through Amazon. £21. About $28.

We shall see what size that turns out to be!
 
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Quick update.

The 20 year old K&N in my RV-6 was 18 1/2" round. I think that has shrunk around 2 inches from the 20+" of the new one!

I now think the bottom plate on the K&N in my FAB is meant to be there as it is exactly the right length for the rib around the new K&N to go around it.
 
Same issue on -10 but K&N says not being used as designed??

500 hours and K&N telling me that I didn't need to clean it if i could clearly see through the filter, which I could. So never cleaned, but sure enough it shrunk enough that I can not use it anymore. I called K&N, based on this feedback from forum and they mentioned the filter is not warrantied due to not being used " as designed" as the E-3450 is not meant to be used as a aircraft filter. I bought a new one from Aircraft Spruce, which fits correctly.
Pascal
RV-10
 
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So is it time for a better mouse trap ?

Just finishing up my 4th Annual inspection and I went to put back my air filter that I had washed and put aside.

LflIuHwFYjRucOPiWZchuFoXXS08P12N7a7GUWT6UdyATy86Ui8Q24M1uo_IpVv_8SerZxWDaC2HLQQAHnvZHpYQjdOjt6qLXxNQ1nS8vT3hOvKeScdrYYM9IXjYr-NgLjbyX3m39gk9E90-HZp0-u6ox4BybJjPIqJBJM0dZog62_MH750llRUwVzeUIA6AFUVhCANhVS7H_MQazJXrwNHY8K-Q2pG2RJDXfIGKu5bySKh-p5GKfM7Pm_WC2JWufHiNzrk7uVOfBSJhHO1v2TUAAZUeEIR84aJT_1W6pqLF7eGBuakJLFvbiKGm5Avjl3yKbTucrm3f2xEGCDRQHnL1TGzLMAeJikXm6A8R_gvDD1ka2OIqfNas1URguZS19dc09MyQSJFVM0AzNH66H5hM9X5Aoacl0ULWwEqjvQuZ_UPly2sShVvCLn69AYXi5SKNiWJMC160sifUwtQp125a1esZXo1HCrkNs-8e7pi14OlPv9DVaRPSiF7gWyGREOfoN_AF09_qKwx1pTnzZcrlrSpV_H2RoRWq3dJsQu1LcN4uUzwANjddXjoS9nIN46FFncHTyzS1UL4VawsRVVLY12Tk8E_dEgf-DaT64SiGHP56oRYs_Czxatdq2Kc9=w813-h609-no


The filter had shrunk in height and length, so much so that I had to put a .063 spacer in the bottom of the FAB on top of the Stainless wear plate that was already fitted just so it would seal.

This is the 2nd filter in 4 years ,the first one shrunk the same way at the 2 year mark.

I do fly through a lot of rain.

Time to look at a total redesign of this area .
 
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I bought a new filter at the first CI. I then cleaned the old filter and let dry as Scott suggests, in the hangar in free air. When dry, after a couple days, I put it back in the box until next year. I then oil the spare and install it (if it is new it is pre-oiled). At the next CI, repeat.
My two filters have lasted 750 hours total and more than ten years with no shrinkage..

I think the takeaway is to do this and if it shrinks take it back to the autoparts store and tell them it was in your car for the warranty.
 
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