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FAB Wear

J

jchang10

Well Known Member
After 150 hours, i noticed that the floor of the FAB is getting a wear spot or two from the air filter rubbing on it. I tried searching for some solutions but no joy.

Has anyone seen this and come up with some good ideas?

I could do a fiberglass patch to reinforce it, but it seems like the problem would just reoccur. Seems like a better solution is to create a stronger floor with Al.

Updated 7/17 with photos.

IMAG0999.jpg


IMAG1005.jpg


Thanks,
Jae
 
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I put .063 on the bottom, which also gave me a place to put the nutplates for the emergency air assembly rather than just rivet into the fiberglass. And I sealed it all with ProSeal.
 
Just curious

Do you use the K&N filter seal (special K&N grease) on the rubber surfaces when you install a new filter? 744 hours and I do see light impressions on the fiberglass but I'm on my third aluminum top.

Bob Axsom
 
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No. This is the first i heard of a filter seal. I just laid the filter on the fiberglass floor since the filter already has the rubber rim. Clearly, the manufactured rubber rim is not sufficient to prevent wear.

Jae

Bob Axsom said:
Do you use the K&N filter seal on the rubber surfaces when you install a new filter? 744 hours and I do see light impressions on the fiberglass but I'm on my third aluminum top.

Bob Axsom
Click to expand...
 
If the fiberglass is wearing from rubbing of the filter, then the filter has been moving back and forth, which indicates the fit is not tight enough between the top and bottom of of the FAB. I discovered I hadnt made mine fit tight enough and simply marked the correct footprint of my filter on the bottom of the FAB, scuff sanded it, mixed up some microballoons, and poured a thin layer in the marked footprint and let it cure. Lightweight, secure and works great.

erich
 
jchang10 said:
No. This is the first i heard of a filter seal. I just laid the filter on the fiberglass floor since the filter already has the rubber rim. Clearly, the manufactured rubber rim is not sufficient to prevent wear.

Jae
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I presume the "filter seal" is the K&N Filter Grease. They recommend it being applied for all automotive installations -

Fit and Finish

When installing a K&N filter, check all gaskets, clamps and seams for damage and/or deterioration. Check the filter's sealing surface. Do not install a filter if the seal shows signs of damage or deterioration. Check for cracks in the air box, particularly at the seams and around the corners. Such defects could cause air leakage around the filter. Also, check to insure the filter is sealing properly in the air box. A plastic air box can warp from age or continuous heat cycling. Apply a thin layer of filter grease on both sides of the seal each time the filter is installed. An impression in the grease will indicate a positive seal.

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Use of the grease is required by STC for some of the certified Challenger (K&N aircraft filters) installations.

The grease is some sort of high temp. stuff and does not melt or get runny under the cowling...

K&N Sealing Grease provides an airtight fit around sealing surfaces on all types of air filter elements. It resists heat and will not melt or run off. K&N sealing grease is not to be used on clamp-on filter elements
 
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erich weaver said:
If the fiberglass is wearing from rubbing of the filter, then the filter has been moving back and forth, which indicates the fit is not tight enough between the top and bottom of of the FAB. I discovered I hadnt made mine fit tight enough and simply marked the correct footprint of my filter on the bottom of the FAB, scuff sanded it, mixed up some microballoons, and poured a thin layer in the marked footprint and let it cure. Lightweight, secure and works great.

erich
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In fact I noticed that the filter seemed to have shrunk by a half inch in diameter. It probably has shrunk in height too possibly causing a more loose fit. Will have to look into it further and/or get a new filter.

Jae
 
Reply from K&N

I emailed K&N tech support to see if they had a clue to why the filter is shrinking in size. Nothing useful.

Hello,

Thank you for your interest in K&N products. The type of fuel and the heat should not cause the filter to shrink, unless the filter was being soaked in gasoline; however without testing the filter to see what happened to the rubber and why, there is no way to really tell. In addition, our filters are not designed for aircraft and do not have any FAA certification of any kind, so there really is no way to know what happened.

If you have any further questions, please reply to this email or call our Customer Support Team at 800-858-3333

Thank you for writing

James Johnston
Product Specialist
K&N Engineering Inc.
www.knfilters.com
Phone: (800) 858-3333
 
FAB wear

Mine started leaving just a mark on it so I cleaned and added some fuel tank sealant. Re-installed filter when cured and no problems in 2 years now.
 
jchang10 said:
...
Thank you for your interest in K&N products. The type of fuel and the heat should not cause the filter to shrink, unless the filter was being soaked in gasoline; however without testing the filter to see what happened to the rubber and why, there is no way to really tell. In addition, our filters are not designed for aircraft and do not have any FAA certification of any kind, so there really is no way to know what happened.

....
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Unless you have a Challenger STC for a certified aircraft in which case the identical filters have the usual K&N part number and a rather untidy "FAA-PMA" melted into the rubber edge....:rolleyes:

I believe my Tiger one is the same as a 60's slant 6 Dodge....:)
 
Mine had a fairly deep groove worn where the filter touches, and had begun to crack in the thin spots. I layed up some more glass inside, problem solved. I'm not a big fan of putting aluminum in there - too much vibration from induction pulses. Vibration = cracks eventually in aluminum, given the high cycle rate.

Also experience the same shrinkage described with the K&N filter.
 
AlexPeterson said:
Mine had a fairly deep groove worn where the filter touches, and had begun to crack in the thin spots. I layed up some more glass inside, problem solved. I'm not a big fan of putting aluminum in there - too much vibration from induction pulses. Vibration = cracks eventually in aluminum, given the high cycle rate.

Also experience the same shrinkage described with the K&N filter.
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Alex, i just saw your reply. I thought I was the only one to ever have seen this. Thus, far it is now just two reports.

Any ideas what the cause may be?

I updated the original post with photos of the shrinkage. Now that i have a new filter and can compare, the difference is significant!

Jae
 
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Two more reports

Jae,

My K&N filter has also shrunk and the FAB is worn from the (now smaller) K&N vibrating. My filter is now slightly conical. I plan to fiberglass and rivet AL in the bottom for the filter to rest against. I also plan to get some grease to improve the seal and possibly reduce future wear.

I asked an airport neighbor, tech counselor about this and he said it was a "common problem" with fuel injected engines that have fuel dumped in the FAB at times. He glassed/riveted AL in the bottom of the FAB in the first plane (RV-6A) he built. I don't think he has done this with the RV-10 or the RV-3B that he subsequently built.

The first picture in your original post looks like there are fuel stains in the bottom of your FAB. I'm guessing that you have a fuel injected engine?

Regards,
 
Roy, thanks for the report. Yes, i have a fuel injected engine. That blue you see is actually just sharpie marks. However, there is definitely a little moisture sitting on the bottom of the box. My box is unpainted and i can see through it. There was no puddle or noticeable amounts other than just wetness, when i pulled the filter off.

I agree about the cause being fuel on the bottom. I notice that the bottom rim of the filter is more shrunk than the top and has become much harder, causing more wear.

For a short-term solution, i created a gasket from some PVC tape or so for the filter to sit on top of. It creates a greater clamping force on the filter as well. Hopefully, it provides some buffer from the fuel on the bottom of the box, too.

Still deciding on the long-term solution.

Jae
 
My filter shrank, too (see photo). I replaced it after 1000 hrs and will replace it more often now because of the shrinkage.
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I had some wear early on but I fastened some stainless steel sheet to the bottom with the fasteners outside the filter itself.
 
jchang10 said:
For a short-term solution, i created a gasket from some PVC tape or so for the filter to sit on top of. It creates a greater clamping force on the filter as well. Hopefully, it provides some buffer from the fuel on the bottom of the box, too.

Still deciding on the long-term solution.

Jae
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Just a caution, Make sure that PVC gasket can not work loose and get sucked into the intake system.
 
Here is what happened to me

I had a wear problem on my FAB and repaired it with FG. I apparently didn't do a very good job and some of the repair flaked off in to thin sheets of resin. Some as big as a nickel. There were symptoms of this. Such as, while in cruise flight I'd sometimes lose a little power and speed and I was always chasing the mixture. The FF varied a lot also. I was about convinced I needed a fuel servo overhaul. I didn't figure it out until one day climbing out of Perry Houston airport I lost most of my power. The engine would only run in the 1200-1300 rpm range and the throttle had little effect except back at near idle position. The engine appeared to be running very lean. I made it back to the airport and did an uneventful SFO. Back on the ground I shut down, checked for contaminated fuel, cleaned all of the fuel filters and strainers, looked in the FAB and did an engine run. It ran fine and I thought it was good to go then all of a sudden it started running bad again including backfiring. I eventually concluded a fuel servo problem and removed the FAB. Once the FAB was off I noticed about 3 large "sheets" of resin stuck on the intake screen. They were blocking some of the intake but more importantly they were covering 3 of the 4 impact tubes for the servo. Amazingly, when I removed these, the engine ran perfectly. I put the FAB in the baggage compartment and flew back to the great state of Texas uneventfully. My solution? I installed an aluminum floor in my FAB and so far so good. BL, my recommendation is a metal repair vs FG. BTW did I say I hate FG. Fly safe.
 
Captain Avgas said:
A good call from John Adams. Sucking up any gasket debris caused by wear on the gasket could really ruin your day.
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Absolutely. It should be a short-term fix, but until then i have added inspecting the filter thru the snorkel on my checklist for now. Thanks!

Jae
 
rvsxer said:
My filter shrank, too (see photo). I replaced it after 1000 hrs and will replace it more often now because of the shrinkage.
Untitled-1.jpg


I had some wear early on but I fastened some stainless steel sheet to the bottom with the fasteners outside the filter itself.
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Anyone have a suggestion on where to get these? I can see that there are a number of places that sell this filter online, but I didn't find the E-3450 at the local O'Reilly or Advance Auto Parts. Neither place even had it in their catalog. Is the web where most people get these? I actually have two already, but neither is round anymore and they have shrunk as shown in the picture Mike posted. I can see that I don't have an adequate seal anymore.
 
I ordered a new filter from Van's. They had the cheapest price but came out as a wash once i paid the $10 for shipping. None of my local auto parts stores carried the right filter.
 
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