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post #1 of 34 (permalink) Old 12-25-2011, 10:36 AM Thread Starter
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Filters 101

There seems to be unnecessary/undue/excessive criticism in my homemade air filter thread, so I wanted to discuss filters in general.

Whether it be oil, fuel or air filters, in all cases they are a compromise between removing unwanted/harmful particles, and restricting flow to the point that they are doing more harm than good.

Two general statements about filters are:

* Large particles are harmful, and
* Small/minute particles are virtually harmless

Also, the mechanics of filter are such that a brand new filter actually filter less than an older/dirty/clogging filter. The reason: older dirt in a filter actually assists the filter media in trapping new dirt. You can see this by holding a brand new filter compared to a dirty filter up to a light and seeing how much light gets through each.

The bottom line is that a filter's precise micron capability is NOT all that critical; you just need to make sure that you have enough filtering capability that you are removing large to medium size particles, without removing such small/minute particles that you are restricting flow, or that the filter will clog in 10 minutes of use and have to cleaned/replaced before continued use, and I am confident that my homemade filter design fits the bill.




Last edited by Aufgeblassen; 12-25-2011 at 12:54 PM.
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post #2 of 34 (permalink) Old 12-25-2011, 11:20 AM
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If you have rode dirt bikes much, there was an old trick that we did, and I still use it on my mowers & cycle... If you have room (You usually do) rub some stiff grease on the insides of the filter cover, you won't believe what will be caught before going to the filter...
Be careful to not get any on the filter itself though... Remember this is not clogging your filter... You should see my mower filter cover when I clean the filter, there is a minimum of 1/4" of dirt on the inside of the cover...
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post #3 of 34 (permalink) Old 12-25-2011, 01:49 PM
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First, you could have put this post in the thread you already started instead of starting another one.

Or you could have at least put this one in the proper section.... as you did not do with the other one ...

That all aside... You cant just judge the filtering qualities of a media by how much light passes through it. A sheet of glass passes alot of light and zero particles....

That aside.... I am sure your homemade filter is better than no filter at all and may even be more efficient at removing " harmful " particles than the stock filter.

But you have no testing data to share other than your seat of the pants opinion. Sorry, but not sure I'd trust my engine on some homemade untested filter...and that was what my point was in your other thread.

If you trust your handiwork that the filter material is strong enough to last or that your glue job will hold...good for you.

Size of the dirt that enters the motor matters less than what it is made of. See you live in Florida....fine sand will do more damage to your motor than stuff like hair or organic matter like pollen, leafs or bird poop dust.

Again, not saying your filter does not work, just saying it's an untested unit and I wouldn't feel comfortable using it. If you can't afford to buy the needed parts for your bike I guess that's another thing entirely.....

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post #4 of 34 (permalink) Old 12-25-2011, 08:50 PM
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You may find some informative materiel on air filters here:
http://www.rc51.org/airfilt.htm

Oil Filter comparisons:
http://www.calsci.com/motorcycleinfo/Filters.html

It is kind of a long read through all of this, but informative if you take the time to really study it.

Gordon

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TOP TEN THINGS A NEW RIDER/OWNER SHOULD DO. Click on link.
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Last edited by OlHossCanada; 12-26-2011 at 12:12 PM.
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post #5 of 34 (permalink) Old 12-25-2011, 09:25 PM Thread Starter
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Quote:
Originally Posted by Knifemaker View Post
fine sand will do more damage to your motor than stuff like hair or organic matter like pollen, leafs or bird poop dust.
Large particles of sand are the ones that actually can cause wear in an engine. I have all the confidence in the world that my filter design blocks them. If the very small/minute particles of sand do indeed pass thru my filter, they do not have enough mass to be of consequence. There is no such thing as a 100.000000000000% efficient filter on any kind.



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post #6 of 34 (permalink) Old 12-25-2011, 09:50 PM
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You will probably be safe in Florida with it. Here in West Texas where one can get caught in a bad dirt storm where sometimes even the road is hard to see, well I am not even sure if the oem filter can accually filter all the dirt out.

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post #7 of 34 (permalink) Old 12-25-2011, 10:54 PM
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Quote:
Originally Posted by Aufgeblassen View Post
There is no such thing as a 100.000000000000% efficient filter on any kind.

Actually there is. There are several types of filters that can remove 100% of fine particles from the air. (and 100% is a defined limit, there's no reason to add a decimal point and more zeros...)

The problem with over efficient filters is they aren't that nessesary on a internal combustion engine, and that they can't filter large volumes of air without being uselessly large. There's no need and no room for a filter that's bigger than the motor it's protecting, especially on a motorcycle where space is limited.

Anyway, if you're happy with your creation that's all that matters. I'll keep using filters specifically designed for my bike as they are tested , warranted , and I don't have to any other work besides just switch them out every X amount of miles if needed.

And I'm not sure your statement that a dirty filter works better than a brand new one is 100% valid. You have any research on this?

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post #8 of 34 (permalink) Old 12-26-2011, 08:44 AM Thread Starter
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If we are discussing which filter removes more dirt, then the dirty filter does. As the filter media captures dirt, the pores through it begin to plug up. As these pores get smaller and smaller, they are able to capture particles that would normally go right through the clean filters larger pores, which results in better filtration. There will be a balance point where the restriction of the filter will become to great and will start to affect performance. Typically this is when the restriction reaches 25" of water column. if is virtually impossible to service/replace an air filter without letting some dirt into the engine, which is why many engine manufacturers recommend that over servicing of air filters be avoided.
One of the things that we often forget is that an air filter is usually sized to deliver adequate airflow with minimal restriction for the greatest amount the engine will need, wide open throttle at high rpm. How often do we drive like this?
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post #9 of 34 (permalink) Old 12-26-2011, 09:54 AM
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Quote:
Originally Posted by Aufgeblassen View Post
........
One of the things that we often forget is that an air filter is usually sized to deliver adequate airflow with minimal restriction for the greatest amount the engine will need, wide open throttle at high rpm. How often do we drive like this?
Some of us.... Most of the time.

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post #10 of 34 (permalink) Old 12-26-2011, 12:22 PM
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Quote:
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Some of us.... Most of the time.

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