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Ever-shrinking K&N air filter - a continuing saga

Lycosaurus

Well Known Member
VAFers have well documented the K&N filter shrinkage. Mine has lasted almost 12 years and it has shrunk a little, though my need for replacement is due to the rubber seal portion having hardened like a rock. Time for a replacement.

So I ordered a replacement filter No. E-3260 for the o-320. Looks like this filter also shrinks during the manufacturing stage. :) This new one is about 0.160" shorter than my older one. Anyone see this too, or am I just lucky? :rolleyes:

This means I need to add additional proseal to the bottom lip of the emergency air intake.
 

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Are you sure you got the right one? I have the Van’s FAB for mi IO-320 and it uses an E-3450.
 
Are you sure you got the right one? I have the Van’s FAB for mi IO-320 and it uses an E-3450.

The dimensions for both models are specified to be 2.5" in height. The new filter measures 2.24", while the old one has shrunk to about 2.4". The E3260 fits the bottom aluminum plate of the filter assembly perfectly, just like the original, therefore I believe I have the correct filter. I will double check my measurements though, and report here if different.

Here are the specs for these filters from the K&N web site (knfilters.com):

E-3260
Height.................. 2.5 in (64 mm)
Inside Diameter..... 5 in (127 mm)
Outside Diameter... 6.375 in (162 mm)

E-3450
Height.................. 2.5 in (64 mm)
Inside Diameter..... 6.25 in (159 mm)
Outside Diameter... 7.75 in (197 mm)
 
E-3250 in E-3260 box?

Did you check the part number on the filter itself? Maybe you got an E-3250 packed in an E-3260 box.
 
Did you check the part number on the filter itself? Maybe you got an E-3250 packed in an E-3260 box.

Hmmm... there were no numbers stamped on the filter that correspond to the model numbers. I may make a call to K&N and find out more on how to identify which filter it is. Thanks for pointing this out.

E-3250
Height..................... 2.25 in (57 mm)
Inside Diameter........ 5 in (127 mm)
Outside Diameter...... 6.375 in (162 mm)
 
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Update

So here is an update...

I checked the box the filter came in, and it looks like the filter number and bar-code was placed over a previous sticker. I tried peeling it off, and it in fact looks like the previous sticker was an E-3250 (look at the 2nd image, with the 2 labels partially removed, exposing the back of the 2nd label... E-3250).

I purchased this filter via Amazon, full-filled by them, came in from California to Canada (could not find that filter in my part of the country). Called K&N tech support regarding the dimensions and my suspicion it was mis-labeled. I informed him that I had purchased the filter from Amazon and that I had started modifying the filter for my off-road vehicle. After checking the specs, the tech took down my contact information and said they would check their stock for quality control, and after checking one filter, they would send one to me as a warranty issue. Wow! Nice on K&N for owning it.

I may have wasted some time and effort on ordering and modifying the first filter, but am pleased they are sending me a replacement. Hopefully I will get some flying done this summer, as my annual inspection has been dragging out for too long now.
 

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I replaced mine last year. Got the new one from Van's. Here they are side by side. The original lasted 6 years.

IMG_8568_heic-M.jpg

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informed him that I had purchased the filter from Amazon and that I had started modifying the filter for my off-road vehicle.
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I may have wasted some time and effort on ordering and modifying the first filter, but am pleased they are sending me a replacement.

How/why are you modifying the filter?

I too need to modify the filter as the slightly off center snout in the filter box from intake snorkel to my Bendix fuel servo puts the heads of two of the bolts that hold on the servo under the filter. I carve out a bit of relief in the rubber upper cap of the filter to accommodate. The good thing is that it really traps in the “ever decreasing” filter. What I don’t like is that I can’t clock the filter differentially each annual to change which section of the filter faces forward and gets all the bugs.
 
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6 years? 12 years!

Why?

There is an aluminum plate that fits on the bottom of the filter. Over time and flight hours, the filter's rubber components shrink and make it so that plate becomes a difficult fit. The rubber has hardens over time, likely to exposure of fuel mist. My old filter had close to 1100 hours.
 
How/why are you modifying the filter?

I too need to modify the filter as the slightly off center snout in the filter box from intake snorkel to my Bendix fuel servo puts the heads of two of the bolts that hold on the servo under the filter. I carve out a bit of relief in the rubber upper cap of the filter to accommodate. The good thing is that it really traps in the “ever decreasing” filter. What I don’t like is that I can’t clock the filter differentially each annual to change which section of the filter faces forward and gets all the bugs.

There is an accelerator pump protruding right where the filter fits, and instructions call for this modification on the MA4-SPA carb'd o-320. See
https://vansairforce.net/community/showthread.php?t=132716
 
Replacement received

Just received the replacement filter (E-3260) from K&N. Looks like they took one off from the production line since the date code indicates June 21st.

Advice: Make sure to actually measure the dimensions of your new filter, as the box may have been mis-labeled as mine was.

Measured the thickness to be 2.46". Good enough to start hacking away at it so it will fit under the carb. Kudos and thanks to K&N.

Thanks to everyone that piped with their comments/ideas on this thread.
 

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Just to add, this must have happened to a whole batch of filters, not just one. Brand new filter purchased direct from K&N UK a month ago, opened box today, exactly same issue.
 
Lucky

I feel lucky, mine came from ACS and was as advertised but I did find it was not quite as high as my old one. Had to add three washers so it would seat.
 
Unlucky this time

I change filter every two years on average. I was unlucky this time ACS sent me a bigger one. Exchange/return would take a lot of time I decided to do a surgery to it.
Sharp blade, safety wire to stitch, a bit of RTV and I have correct diameter :)

filter_-_1_(1).jpeg


filter_-_1.jpeg
 
Seems to be quite an issue with K&N quality control if we are all ordering the right size filters, and receiving smaller and larger than spec!
 
You can take the Russian out of the Motherland, but you can't take the ingenuity out of the Russian.

Impressive surgery, Vlad.
 
RTV + Fuel = Mush

Hey Vlad,

I would keep an eye on that RTV seam. Any contact with fuel would turn it to mush. Injesting a blob of RTV could cause a problem. It might just pass through the system or create a problem. I think there was a previous post about an RTV blob getting stuck in a portion of the venturi in the throat of the carb causing a power outage. Take care!

Mike
 
Hey Vlad,

I would keep an eye on that RTV seam. Any contact with fuel would turn it to mush. Injesting a blob of RTV could cause a problem. It might just pass through the system or create a problem. I think there was a previous post about an RTV blob getting stuck in a portion of the venturi in the throat of the carb causing a power outage. Take care!

Mike

Thanks Mike appreciate the reminder. I am aware of it. The seam is closed shut inside without any RTV protruding. How have you been? How is CJ haven't heard from him for a while.

Mike's_Eight_-_1.jpeg
 
HA! Love that picture, I miss the -8.

I am well thanks and I hope the same is true for you. About two years ago I moved to New Zealand for a 6-8 month project. Covid came along as did an opportunity to extend my stay.

I've done a little bit of flying in NZ but not much. I've spent most of my free time exploring the north and south islands. It is a breathtaking, amazing country.

Just booked my return flight. Haven't heard much from CJ. I think the love of his life is keeping him busy ;)
 
Hey Vlad,

I would keep an eye on that RTV seam. Any contact with fuel would turn it to mush. Injesting a blob of RTV could cause a problem. It might just pass through the system or create a problem. I think there was a previous post about an RTV blob getting stuck in a portion of the venturi in the throat of the carb causing a power outage. Take care!

Mike

I agree. That is not a good solution. Good chance of a piece of RTV or a piece of safety wire being sucked into the fuel servo. That's an area of extreme vibration. There's so much vibration of the air filters that it's not uncommon for the filter to wear right through the bottom of the filtered air box.
 
Air filter RTV

Vlad,

Like Mike said, keep a VERY close eye on that RTV. I seem to remember a post on this forum quite some time ago about a guy that did something similar and eventually the RTV disintegrated and got sucked into the throttle body and ended up with a rough running engine and had to clean rtv debris out of the engine.

You fly to some pretty isolated places so maybe waiting for the correct size filter might be a better idea. Just my two cents.........
 
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