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Converting Air Filter from Oil to Paper


Sam Buchanan

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Since my P15 doesn't spend any time on dirt roads, and the oil-bath filter is sort of a pain to service, I decided to convert it to a paper filter. I did a lot of searching in the forum archives but the threads I found were several years old and most of the photos can no longer be accessed. I took photos of the method I used in the conversion so current and future members will be able to get ideas about how to do the conversion.

 

We need a filter element that has the proper diameter to drop into the recess in the bottom of the lower filter bowl. The height of the element isn't critical, I suspect if it is at least three inches high it can accomodate the torrent of air roaring down the throat of the one-inch bore of the carb.  ? 

 

At my local family-owned auto parts/lawn equipment dealer I found a Kohler filter for some sort of lawn machine that was a perfect fit.

 

paperfilter-1.jpg.38df70c8112f3436bcb821381d53f91f.jpg

 

A cap for the filter was cut from 1/8" aluminum, but any metalic stock would be fine if it is fairly stiff.

 

paperfilter-2.jpg.200b3af94648a53b89b2bd92fea9a67b.jpg

 

The top half of the old filter must be modified to accomodate the new paper filter. I used tape to establish a cut line on the upper bowl.

 

paperfilter-3.jpg.6ae8414f7f9e2fb2bbccde95077ef82f.jpg

 

The cut-off wheel easily cut the bowl and the old fiber element was set aside.

 

paperfilter-4.jpg.58ef3fed8837853f62b3ace438be87c6.jpg

 

I put the modified top back on the lower bowl, made sure it was fully seated and took a measurement of the protruding end of the stud.

 

paperfilter-5.jpg.2a910e87341d1959e65def17c3fb372b.jpg

 

The top was removed, the wing nut run down to the measurement I had taken, and another measurement was taken of the space between the bottom of the nut and the filter cap. This indicates how long a spacer is needed to fill the gap between the cap and filter lid.

 

paperfilter-7.jpg.b2511d1be40041b568252d9527daacdd.jpg

 

The top lid was placed in position, the wing nut run down snug and the new, oil-less filter assembly installed back on the carb. This mod retains the original appearance of the filter, nobody can tell there is a modern paper element inside.

 

paperfilter-8.jpg.f29b208438021d657853c9878e55e1b3.jpg

 

A test drive proved the P15 is happy with its new filter and it should be good for many years of maintenence-free filtering.

Edited by Sam Buchanan
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I used a WIX #42221. After cutting a disc like Sam shows, I looked down and saw a 1 gallon paint bucket. A quick measurement and yup I could have used the lid.

I also have a shorter housing, on the backup shelf, and I believe the same filter will work in it as well.

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Very nice job there, Sam.  Thanks so much for posting how you accomplished this.  I was kinda lucky in a way that our D24 did not have an air filter at all when we got it - I didn't have to fret over a conversion.  I ended up getting a period aftermarket Fram dry air filter off of an F6 in a farmer's junk yard, and got a case of filter elements for it that I still haven't gone through.  Didn't find an original oil bath filter until many years later, which has been sitting on the spare parts shelf.  Our Terraplane has the original dry air filter, that looks like an oil bath one.  Actually, I think it's more of a silencer, because even new, it couldn't have been a good air filter.  I need to devise a way to get a modern element in it, your post will help!

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16 hours ago, LazyK said:

I used a WIX #42221. After cutting a disc like Sam shows, I looked down and saw a 1 gallon paint bucket. A quick measurement and yup I could have used the lid.

I also have a shorter housing, on the backup shelf, and I believe the same filter will work in it as well.

 

The Kohler filter I used sure looks like a rebranded Wix 42221. The paint can lid is a good tip.   :)

 

Anyone considering this conversion should use a metallic disc so a carb backfire can't distort the lid.   

Edited by Sam Buchanan
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1 hour ago, chrysler1941 said:

Wouldn't be better to address this problem? Carbs shouldn't backfire.

 

I agree and I've never had a backfire with my car.

 

But can you say with certainty that a backfire will never happen?

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The main reason for my "metallic disk" comment was the implication not to use some sort of plastic-like material. It would function fine on the filter until exposed to high temp which could make it distort and lose tension holding the element in place.

 

Yep, purist will prefer the oil bath filter. But I really like having a modern, maintence-free for all practical purposes, filter element that doesn't detract from the original look. It's good to have options.  ? 

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the oil bath filter is still common in many commercial and agriculture circles due to the fact they are much better filters.   But I also see and understand the trend to go with the paper...and in the town/urban communities of paved roads and few plowed fields of stirred dust lingering over the highways....it a suitable means to filter the air.  But for certain the oil bath will win in all aspects except cleaning and servicing.

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