No more foam air filters for me!

[Schneller]

Group,

We use K&N filters in most of our customer race cars. As long as they are cleaned & oiled regularly they seem to work OK. However, they do pass more dirt.

Last year 2 of our cars raced at the new Calabogie circuit in Canada. The track was new & the surface was releasing a fine grit which afterwards was all over the engine bays of both cars. Sad to say we also emptied many OUNCES of the grit from INSIDE the intake manifolds of both cars! This stuff was able to penetrate the oil soaked weave of the K&N filters. Higher flowing filters have bigger air passages & hence allow bigger particles to pass through .

Also, w/ the K&N filter, you just can't drop it in & forget it. As they get dirty, their flow characteristics drop dramatically. We had an M5 w/ a K&N filter that hadn't been cleaned in 4 months and the HC's were too high (running too rich). Cleaning & re-oiling the filter restored emissions to spec (more air flow leaned the mixture). If you ride a lot, how many of you clean your air filters every 2 months or so? The filter on an S bike isn't the most convenient item to service.

It's my opinion that paper filters are a safer bet & that's what I run in my bike & car.

Schneller

[Deans BMW]

It's my opinion that paper filters are a safer bet & that's what I run in my bike & car.

Me too.

[BMW Atlanta]

Originally Posted by Deans BMW

Me too.

Try telling that to the couple of HP2 Enduro and GS owners who sucked in a little bit of water and the paper got swallowed immediately. In one case there were two HP2 E's on the same water crossing at the same speed, one had paper one had UniFilter Foam and the one with paper got treated to an engine rebuild after the day.

We've seen paper filters on the GS's and S's get wet just riding in terrential rain, this severely tweaks the filteration properties and integrity of the stock paper filter.

Also comparing the foam filters, in our experiences foam passes less debris then any cotton gauze type filters like K&N. You can't buy a main stream dirtbike with a paper or K&N filter (let alone even find K&N for current day dirtbikes), thus when filteration is most critical, foam is the only option while paper is cheaper and less maintenance, it's more prone to integrity issues given the wrong environment.

Foam may not be for everyone, but this would be the first Foam filter to have an adverse result.

Just give me a ring and we'll get it swapped out

[hawkeyejohn14]

Originally Posted by Schneller

It's my opinion that paper filters are a safer bet & that's what I run in my bike & car.

I as well run the stock filters as suggested by a Great BMW mechanic in Atlanta before there was a BMW of Atlanta and Bobby was still in grade school. Due to the reasons mentioned above about letting to much crap into the engine.

[shreddr]

Foam is the filter media of choice for dirt bikes because it has the smallest pore size combined with the ability to withstand water (the water still gets sucked in, it just doesn't foul the filter). As BMW is not afraid of throwing lots of routine maintenance at the owners, it doesnt make sense that the paper filter was an oversight, or some cost saving measure, the HP2S has one forgodsakes! The paper filter is in fact the BEST filtering media for eliminating the smallest particles and still allowing sufficient airflow. It rains plenty in Germany, and Europe, if the paper filter was an issue there would be a European option for those riders constantly fouling their paper filters, but they don't offer one, because one isn't needed.

When I first started racing MX in 1975 I got a "trick" K&N filter for my Elsinore 250, assuming of course it would give me better performance (it wouldn't have mattered anyway) Imagine my horror when after the first dusty race I ran, I took the filter off and saw dirt deposits in the back end of the carb! The K&N design hasn't changed much in that time.

If you want an alternative filter because you think your bike is starving for air, you are more than likely incorrect (unless of course you have made some HUGE flow improvements to the heads). If you think an alternative filter will filter better than the stocker, you ARE incorrect. If you think an alternative filter looks cooler than paper, and the cool sticker that comes with them looks good on the bike, you are right. You pay your money and you take your choice.

[JonyRR]

there's no doubt in my mind at all that a paper-type (and that includes oiled gauze such as K&N) pass more dirt than a properly oiled foam filter.
With any modern foam filter, it's important to clean it with the recommended cleaner. gasoline tends to dissolve the glue that holds the edges together.
None of MY dirt bikes will ever get a K&N type filter. I feel safe running paper or oiled-gauze on a streetbike as it will never be subjected to the rigors of the offroad environment, but I still worry about passing water during a torrential rain with a K&N..and they WILL pass water if abused enough.
This sounds like a freak failure.
Now that I run electrostatic foam at the outside end of a big schnorkel, we'll see how THAT setup works long-term.
Nikasil does NOT like dirty air, BTW.
tire threads
oil threads
air filter threads
spark plug threads
it's a religion!

[Deans BMW]

Bobby, the San Jose race bikes use your foam filters.

[kocook]

Originally Posted by AZ-Twin

How many times have you cleaned it, and if any what did you clean it with?

My first thought also.

If you use the wrong cleaner with these, the glue will breakdown. The instructions are pretty clear on that. I am fortunate that the local CycleGear store sells Unifilter products so I can use the manufacturer's cleaner and oil. Still I check the foam's adherence to the mount every time I clean it. It is a potential weak point.

[OwenM]

There is more then just a filtering efficiency issue here, I replaced a BMC cotton wire filter with a Unifilter foam filter and my R12S runs better, no question. I believe its because the foam filter damps the resonances in the air box, not because it flows more air.

[zx9rmal]

<>

Rob -

I cleaned it once, maybe 6-8K miles ago, with Honda foam air filter cleaner.

[zx9rmal]

Originally Posted by BMW Atlanta

Very abnormal and the first I or Uni has heard of such a failure. It is possible the knife cut too far when making the foam cylinders that comprise the filtering media. We have MANY of these filters out there in use and as long as you remember to take out the internal spring when you clean the filter and do a good inspection (knowing what to look for) upon re-installation these filters will give many years of great flow with superior filtering abilities. Send it back if you can and I'll gladly send you another to replace it.

Thanks Bobby. I appreciate the offer. When I pick up the bike, I'll have a look at the filter to see what happened. At this point, I have no idea so I can't/won't speculate. More will be revealed.

[AZ-Twin]

Mal,
I was just curious as I had one fall apart on my old XT, I used to wash it in gas. I use Mineral Spirits to clean the one in my DR (OEM), it is almost 5 years old and still in good shape.

[geothepencil]

I'll bet your mice don't eat the foam filters as enthusiastically as they do the paper ones. I've always just washed the small engine foam filters I have in dishwashing liquid. Easy on your hands and works pretty good too.

geo

[zx9rmal]

Update. I haven't picked up the bike yet, but the service guy tells me that one of the 2 pods separated from the filter body and got sucked into the right throttlebody. The spring somehow stayed a bit upstream from the throttlebody........thankfully. They say the bike is fine. I say.......I hope so. I'll get the filter back tomorrow or Saturday and post what I see. I'll send it back to Bobby so he can see what happened. As long as the bike is OK, no harm done. I only paid for an hour of labor. No big deal. Had them warranty the antenna ring while they were at it.