This is why I did this “test”.
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Ever since I built the KX-200, I have used a KX air filter, KX air box and KDX air boot. A while back, I decided to try a different approach since I had the parts laying around – I put together a new system that used the KX air box, but used the KDX air boot and the KDX air filter. Since I have never used the KDX air filter before, I did some reading and decided to try a UNI filter for the first time.
Up until this change, I never had problems with dirt getting past the air filter. So either the air filter is at fault or the design of my new air intake system is at fault. I couldn’t wrap my head around how to easily do a leak or pressure test on the air boot / air box, so looking at the air filter seemed like an easier starting point. I originally wasn’t trying to compare air filters, I was just looking to determine where dirt was getting into my engine. But as usual, things spiraled.
My approach to testing is very low-tech. It doesn’t get much more basic than a wet/dry vac and grease. But since my goal was only to identify where dirt was entering my intake system (in this case was dirt passing through the air filter?) did it need to be any more complicated???
If I were trying to determine air flow or the total amount of particles passing through the filter or the size of the particles passing through the filter, I would need something from a lab at Consumer Reports.
The one thing I proved to myself is that not all air filters are the same. As you will read, you can take a flash light or a light bulb and compare different filters and see that some use foam with larger cells and others use foam with smaller cells.
And even the same air filter can have very different results when the method for sealing the bolt hole is changed. In the case of the KDX air filter, foam with a hole punched in is inferior to the more common practice of using a rubber grommet that is found in most other air filter applications.
And I certainly questioned my oiling technique. But if anything, I would claim my filters are over-oiled. I say that because I’ve handled a few pre-oiled filters and they seem exceptionally dry. Here is how I do it:
Start with a clean filter:
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Get a small container and the FFT:
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Empty the bottle in the container:
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Completely saturate the air filter:
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Squeeze the filter until no more oil drips out:
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Let the filter sit for a couple of minutes and then blot off the excess oil:
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Finished:
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Enough of my rambling and on with the results.
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The last two times I’ve gone riding (this time and that time), dirt has gotten through my carb and into the engine. It just so happens that I bought a new UNI filter two rides ago. Placing the oiled UNI filter in front of a halogen light revealed more spots of bright light than I expected:
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After seeing this, I dug up an old Moose Racing air filter that came with one of the KX airboxes I bought on eBay:
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Placing this dry filter in front of the same halogen light revealed no spots of bright light. You can see dirt, but no direct light.
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I was going to order a Twin Air, but after seeing how this Moose Racing filter looked, I thought I’d get one of those as well.
A few days later, I’ve got all the filters to test.
Twin Air:
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Moose Racing:
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The comparison of the sealing surface (Moose on the right):
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Halogen Light Test
I’ve already seen how bad the oiled UNI filter looks. Here is what the same UNI filter looks like dry:
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Here is what the dry Twin Air looks like in front of the halogen light. Still has bright light spots showing through, but not as bad as the UNI:
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Here is what a dry Moose Racing looks like in front of the halogen light. The cells or pores of the foam material look smaller/finer than the other two. I don’t see any bight light spots showing through like the other two, but the yellow color of the filter may be masking that. Time will soon tell:
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Testing
I’m glad I didn’t pitch the OEM filter base, I found a good use for it:
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And finally all this goes together so that the filter sucks up dust from the bucket when the mortar mix is stirred up:
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And to see what might be getting through the filter, I used these pieces of lightly greased white plastic over the opening.
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I was going to use dirt to do my testing, but then remembered something better. Anyone who has mixed a bag of concrete knows how dusty that can be. This should provide plenty of fine particles:
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A couple of pounds of mortar mix in the bottom of a bucket and almost ready to get started testing:
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Test 1
The UNI will go first:
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After sucking in some dust for a while:
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And this is what showed up on the pieces of plastic:
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Twin Air next:
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And this is what showed up on the pieces of plastic:
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Moose Racing Last:
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And this is what showed up on the pieces of plastic:
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Test 1 Results:
Based on the light test, it wasn’t surprising to see that the UNI let the most dirt through and the Moose Racing did the best. But I have two concerns how I did this test. First, as careful as I was in pulling the dirty air filter off, I was concerned that some dirt could have fallen off the filter and landed on the greased strip, making it look worse than it is. Second, I noticed that with each test, the mortar mix because “denser” and packed in tighter in the bottom of the bucket. This was due to the lighter particles being sucked up and the heavier particles staying behind. This didn’t make for a fair comparison between the 1st filter and the last.
Test 2
To address the two concerns I had, I made the following changes. After each test, I will dump the mortar mix out and pour in fresh mix. I also moved the white plastic strip to a different location so I couldn’t accidentally contaminate it:
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UNI first:
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Twin Air second:
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Moose Racing last:
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Test 2 Results:
I guess the good news is that the results from test 2 are somewhat consistent with test one. The Moose Racing did the best but this time it looks like the UNI and Twin Air performed similar to each other. The bad is that even the best performing filter let dirt through.
Time for test 3.
Test 3
During one of the clean-ups between tests, I noticed that there was some dirt/debris in the threads of this piece:
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I’m not sure if that was there from long ago or if the motar mix was getting sucked past the threads. So to test if this was the source of the problem, I turned to a lot of grease to try to seal things up. This test was done only on the UNI filter.
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New mortar mix in the bucket and fresh grease on the white plastic:
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After creating and sucking up a lot of dust:
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Not the results I was hoping for:
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I’m running out of ideas on why so much debris is getting past all of these filters. One final thing to test.
Test 4
Even though I thought I used enough grease to seal up the bolt hole in the center of the air filter, I remembered that the KX air filters use a rubber grommet as seen with this old Moose filter:
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Not having much to loose, I thought I would convert the KDX air filter to use this same grommet.
This is the grommet removed from the filter:
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And this is the center post of the KX air filter cage:
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The grommet fits over the center post like this to provide a fairly tight seal:
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First step is making the center hole in the KDX air filter larger. I thought I was going to have to break-out the exacto knife, but I had a piece of stainless steel tubing that happened to have the right OD:
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Using the Twin Air as a guinea pig, line things up:
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Then press and twist the tubing until it cuts all the foam filter:
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Then insert the grommet:
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The same procedure was repeated with the Moose Racing filter.
Now on to the KDX filter cage. That “ring” on the top is going to cause some problems:
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After a little dremel work:
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Then I cut off the top part of the KX center post:
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It is difficult to tell from this picture, but I drilled out most of the center post:
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So that it would press fit onto the brass part of the KDX cage. It took a lot of force to press it on, so it isn’t going anywhere. Just needs to be cleaned up:
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The modified Twin Air on the modified filter cage:
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So on to the testing. The Twin is first. Fresh grease and an oiled filter read to go.
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After sucking up more mortar mix:
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I still found some debris in the grease, but it was a big improvement.
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Results from test 2 for the Twin Air for comparison:
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The Moose Racing was next. Again fresh grease and fresh oil in the filter:
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After more mortar mix dust sucking . . .
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Finally, the grease is clean!!!
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Conclusion
Each filter was tested three times. After making adjustments after the first test, I think I had an effective and repeatable way of testing and comparing the filters.
The “light” test supported the actual filters in action. The UNI filter looked the most porous in front of a light, and the dust tests showed that it let the most fine particles through. The Twin Air looked better in front of the halogen lamp, but in the dust test, it still let an unacceptable amount of fine particles slip through. Based on the light test, the Moose Racing filter looked like it would do the best out of the three. And the actual dust test supported that.
The UNI filter is going in the trash. I’ll keep the Twin Air, but use it only when conditions are muddy. And I’ll be buying another Moose Racing filter. And before you say “I’m not putting anything Moose on my bike, especially an air filter”, Moose doesn’t make most of what they sell, they just re-brand products. The Moose air filters are actually made by DT-1. Now I just need to find some extra grommets used in the KX filters . . .
NoToil Test 12.30.13
I need to thank Adam728 from kdxrider.net for sending me a NoToil filter to test. This was from a YZ, but looks like it will fit the KDX filter cage:
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Doing the same light test as the other three filters would indicate that this will do a good job of keeping the fine dust out. This is the dry NoToil:
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I only have one KDX filter cage and it has been modified to use that rubber grommet, so I needed to make the hole larger on this filter:
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Oiled up and almost ready to test:
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The YZ filter fit the cage well enough to not cause any leaks or gaps:
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Grommet installed and almost ready to test:
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NoToil mounted up and ready to go:
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Fresh grease for testing:
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After sucking mortar dust for a while this is what the filter looked like:
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And the results:
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Conclusion . . . Confirmed
The simple light test seems to be a good indicator of how well the filter will filter. If the foam cells are large or have large spaces between them that allow direct light to pass through, then dirt can pass through as well. The UNI and Twin Air support this.
Small foam cells or tightly arranged foam cells that do not allow direct light through will due a better job of filtering small dirt/dust particles. The Moose and NoToil support this.
I also need to point out that the factory KDX method of sealing around the bolt hole was problematic. Once I incorporated the rubber grommet, the results of any filter tested improved.