[647jc]

Decided to order a replacement FAB-320-1 Air Box kit and start over again. I ended up with a throat opening at the front where it is supposed to meet with the cowl opening, ½” to high. That is the opening is 2 ¾ inches high instead of 2 ¼”, the top edge of the opening lines up with the top edge of the cowl opening but the bottom edge of the opening almost touches the cowl bottom and is 1/2" below the cowl opening. Where I went wrong is fitting the top plate to the FG bottom, sandwiching the K&N Filter E-3260 in between. The instructions said to compress the filter 1/16” (no way) but I did press the top plate down hard onto the filter sitting in the FB base. While doing this I noticed the top plate was not level so I finally took the filter out and measured it. It is supposed to be 2 ½ tall but mine measured 2 5/8” on one end and 180 degrees from that, 2 7/16”, a 3/16” difference in height. So no matter how I oriented the filter, the top plate would never fit level. I decided the taller end of the filter should go to the front thus making the throat taller rather than shorter and possibly restricting the air way. As it turns out the filter height difference resulted in an air way ½” to high. Had I placed the filter tall end to the rear, everything would have worked out perfect (I think).

So, my question is, are all of these K&N E-3260 filters lopsided like mine or was I just lucky? My replacement FAB kit will have a new filter with it but the suspense is just killing me. What if I you build your air box to tightly seal a lopsided filter and then have to replace it later and the replacement is NOT lopsided? I suspect K&N may have some quality issues but am not sure.

 

[gmcjetpilot]

Make it fit, get a bigger hammer!

Decided to order a replacement FAB-320-1 Air Box kit and start over again. I ended up with a throat opening at the front where it is supposed to meet with the cowl opening, ½” to high. That is the opening is 2 ¾ inches high instead of 2 ¼”, the top edge of the opening lines up with the top edge of the cowl opening but the bottom edge of the opening almost touches the cowl bottom and is 1/2" below the cowl opening.

I think I understand. Generically, builders some times miss the aim a little and physically cut the box, doing a little fiberglassing to make the "snorkel" end of the box align with the scoop. 20/20 hindsight, fit the cowl first with the scoop, than use the cowl to align the air box. However if you are not off left/right you can re-angle the snorkel up or down. Cut the fiberglass and re-angle. Or the big hammer method, bending of the metal to "tweak" it, making it fit will get you a little change in elevation. It's about making it fit. Also remember the engine will sag a little over time. In the "old days" builders had to bond the scoop on the cowl, so you had some play with both scoop and air box, meeting halfway. Of course the Lyc sump is not center line symmetric any way, it's offset slightly.

Where I went wrong is fitting the top plate to the FG bottom, sandwiching the K&N Filter E-3260 in between. The instructions said to compress the filter 1/16” (no way) but I did press the top plate down hard onto the filter sitting in the FB base. While doing this I noticed the top plate was not level so I finally took the filter out and measured it. It is supposed to be 2 ½ tall but mine measured 2 5/8” on one end and 180 degrees from that, 2 7/16”, a 3/16” difference in height.

Totally weird. I believe you but very surprised. I'm not affiliate with K&N nor have I had my hands on more than 3 or 4 of them. I never measured them but they always seemed to be pretty symmetric and uniform in thickness.

So no matter how I oriented the filter, the top plate would never fit level. I decided the taller end of the filter should go to the front thus making the throat taller rather than shorter and possibly restricting the air way. As it turns out the filter height difference resulted in an air way ½” to high. Had I placed the filter tall end to the rear, everything would have worked out perfect (I think).

I guess aiming or building the box to fit around an air filter thickness variation was a small boo-boo, no offense, but it hardly sounds fatal. A tight fit between hard parts (cowl inner scoop lip and FAB) can actually be bad. The engine moves a lot. Also if the seal is too tight, making the cowl and FAB seal ridged, with no give, vibrations will tear-up the FAB. Having a little longer seal that is not too tight may not seal the air as well, but it isolates and protects the FAB from forces induced by engine movement. A mod I recommend is a strut from the engine to the fwd part of air box to give another support point, stabilizing the cantilevered snorkel part of the FAB. Other wise its all flexing off the flat plate bolted to the carb. Flat plate in bending with holes in? This equals crack making.

So, my question is, are all of these K&N E-3260 filters lopsided like mine or was I just lucky? My replacement FAB kit will have a new filter with it but the suspense is just killing me. What if I you build your air box to tightly seal a lopsided filter and then have to replace it later and the replacement is NOT lopsided? I suspect K&N may have some quality issues but am not sure.

That filter should 2.50 thick give take a little, if not send it back. There should be enough give it should seal in a box with to level surfaces. K&N has as good to very good reputation. I think K&N should be able to make a filter with a constant thickness and near parallel top and bottom edges. This is not rocket science, . May I suggest you call K&N and tell them of your problem. K&N Contact Link Could it be a bad China knockoff? I am not joking. It happens and counterfeit parts show up in aerospace and auto-parts all the time.

I believe Van uses a K&N filter for the FAB 320 is the K&N E-3450.

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
Filter Re-Oiling Amount: 0.65 oz (19 ml)
Weight: 1 lb (0.5 kg)

 

[L.Adamson]

I think K&N should be able to make a filter with a constant thickness and near parallel top and bottom edges.

I'm going to assume, that a high point on these filters can also be compressed somewhat (in addition to the 1/16" compression), considering the non-rigid materials they're made of.

L.Adamson

 

[647jc]

Hi George,

Thanks for the input. I think the K&N Filter part number is E-3260 (for the O-320 engine), that’s the K&N number and Vans part number is the same. Yes, I strongly debated slicing the FB throat and bending it up to the correct throat height and then resealing it with a few FB lay-ups. But, I was concerned about building the box to fit an abnormal shaped Filter. So, I decided to at least order a new filter to compare with. I suspect the new filter will not be lopsided in which case my FB tub will no longer fit and since I had trimmed it to fit the lopsided filter, I would have to build back up the rear edge to accommodate the new filter. Also, I had already fit the carb heat door and cut the hole in the top plate for it, unfortunately the door and matching hole are now ½” to high also so, a new door and new top plate would also be needed. Finally, I had already screwed up the mounting plate by drilling it for nut plates, no big deal but I planned to replace it also. So, a new mounting plate, a new top plate, a new FB base and a new filter, sounds like a new kit to me.

Compressing this filter is a real challenge. Pressing down as hard as I could probably only resulted in 1/32" compression at most. Compressing it by 1/16" as the instructions state will take quite a bit of pressure and ultimately the FB base will have to hold that compression which I doubt if it will, it will probably just deform. There is no way I can compress the lopsided filter by 1/8" as needed to make it flat or flatter since the other side is 2 7/16" rather than 2 1/2".

 

[gmcjetpilot]

heck you are right

Oh my thanks for the pic. sorry to even doubt you. it looks like the real deal, lopsided to heck. sorry for your grief. You'll get it perfect next time but return that filter for refund or credit, it's stupid! Just remember building is fun and it will be worth it. Forget compressing it; I agree it's off way too much. You really just want the filter synched in there snug, not compressed to an inch of its life with lots of pre-stressed and load on the plate and airbox. The filter is clearly junk. Cheers

 

[647jc]

Replacement kit filter much better

Just a quick update; received the new FAB-320-1 Air Box kit from Van yesterday. The K&N Filter included with the new kit is NOT lopsided like the original and the whole Air Box is going together much better than the original. I probably should have stopped working on the original Air Box as soon as I determined the filter was lopsided and got that resolved before trying to complete the Air Box with the suspect filter. Glad I started over with a new kit albeit a bit expensive, perhaps I can get a credit from K&N or Van for the defective filter.