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Air filter - does size matter?

bgary

Advanced Beginner
Blogs Author
My air filter is looking a little ratty. I did my usual beginning-of-the-year cleaning (basically blew it out with some compressed air).

Last night I looked online to see what a replacement costs. And couldn’t find one like it (it’s a circular K&N clamp on). I can find smaller ones, taller ones, oval-shaped ones, but not a match.

Current thinking is is that size and shape probably don’t matter, as long as it fits and doesn’t restrict air flow. So I’m leaning toward getting a narrower-but-taller one which, at least mathematically, has more intake area than the old one.

But it thought I’d ask The Collected Wisdom: is there any downside to having a bigger air filter (i.e. one which -theoretically - would allow more air into the intake)?

Bruce
 
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Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Yes to more air

When I was "into cars" as a sort of hobby many decades ago, lowered resistance to the air flow going into an engine was always considered a "good thing".... :nerd:
 

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
That K&N was recommended by Maine Sail and is the one on my current boat. Not that he's infallible.

I think it is intended to be oiled, maybe cleaned and oiled, periodically.
 
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sharonov

Member II
I use K&N RU-2450 on my M25XP. Replaced original metal can filter that was missing actual filtering material in 2016. Did not notice any difference except feeling better about it.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Air Cleaner Caution

Not to get all dramatic on you, but if *anyone* has one of those Universal filter assemblies with the aluminum mesh inside, Remove that mesh. Immediately. :eek:

This applies to the M25XP and possibly the M25. Not sure if Universal used this on their other engines, and I know of owners who say their filter does not have this. (Or a prior owner removed it).



While we will not know, sort of for sure, until the recipient of my old engine tears it down, my mechanic said that our crankcase blow-by problem for many years was likely caused by cylinder scoring from the pieces of that original mesh getting sucked in.

I would advise anyone with an 80's engine from this series to overhaul their air cleaner... or just replace it with a K&N.
 
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debonAir

Member III
Interesting. I have my "air cleaner" off while I replace the timing gear cover. The air cleaner is nothing more than an egg-shaped metal box with a small mesh screen at the pointed end of the box. Anything smaller then about 1/16" diameter would get right into the engine I imagine? I think adapting any sort of air filter would be better than this thing? And this small mesh screen is nearly blocked with grease from the "breather" tube which Universal re-routed to under the air intake screen (the tractor shows it pointing down to grease the farm I guess). I suppose that's better than the bilge but now needs some cleaning.

For the people that have adapted an auto style cone filter.. what did you do with the breather tube?

airintake.jpg
 

bigd14

Contributing Partner
Blogs Author
I threaded a brass hose barbed elbow into the rubber portion of the K&N filter and ran the breather tube to that. I believe I got the idea from Maine Sail's website.
 

Kenneth K

1985 32-3, Puget Sound
Blogs Author
K&N RU-2450 Universal Clamp-On Air Filter: Oval Straight $39.99
https://www.amazon.com/gp/product/B00062YQRA/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

That's about $12 more than the first one I bought a few years ago. Buy the K&N filter cleaner and you can clean and re-use.

Like Bigd14 said, you can drill and screw a hose barb into the flat underside and connect the breather tube directly to the filter.

410DTH3sD5L.jpg
 

kiwisailor

Member III
Blogs Author

bgary

Advanced Beginner
Blogs Author
Its a slip-on fit for an M25 in an E32-3.

Yes. Don't know about the M25XP, but the intake on my M25 is 1-3/4" in diameter, so any slip-on with a 1-3/4" ID flange will work.

I like the K&N stuff too.

Bruce
 

Second Star

Member III
I ran my breather hose down into a clear recycled plastic bottle zip tied onto one of the fwd engine mounts (M-18). This keeps the filter a bit cleaner and collects the very small amount of oil from the hose. Not sure if removing it from the air flow makes much difference to the engine … PCV is an emissions feature is it not?
 

vanilladuck

E32-3 / San Francisco
Blogs Author
Just making the rounds on my Universal M25 after having the mixing elbow, water trap exhaust and alternator bracket changed out. Like most, the air filter contraption is bumbling around atop the engine with no real ability to filter air and more potential to imbue disaster into the intake manifold ;)

Figured I would update and thank the contributors here. Thanks!

I'm ordering the K&N RU-2450 Ken lists above above (https://www.amazon.com/gp/product/B00062YQRA)
 

Geoff W.

Makes Up For It With Enthusiasm
Blogs Author
I use K&N RU-2450 on my M25XP. Replaced original metal can filter that was missing actual filtering material in 2016. Did not notice any difference except feeling better about it.

I use this same filter on mine. It seems a little small, and I'd like to replace it with something slightly bigger, but I haven't noticed any ill effects.
 

Kenneth K

1985 32-3, Puget Sound
Blogs Author
I don't oil mine for 2 reasons. 1st is that the cloth media K&N uses looks like it's much finer of a mesh than the initial installation air cleaners on the universal engines. 2nd, the main contaminant seems to me to be belt dust, which it appears the paper media can trap. I think a mixture of oil and belt dust would be a greasy mess, and maybe cause more blockage to the filter.

K&N offers a filter cleaning fluid, which makes these filters reusable, I cleaned mine two year ago, and was shocked at how much black crud came out of it.
 
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