Currently reinstalling overhauled Lycoming B1E on a RV-7. I need to replace the Rod Bower filter. I am having a hard time finding a replacement filter that actually fits like the original filter. According to K&N, the replacement filter model number is K&N 4250. That filter is slightly “fatter“ than the original filter, which seems to decrease space/volume inside Rod Bower setup. Any ideas where I can get the correct replacement filter? Will the K&N filter work without creating an airflow issue through the reeds when ram air is closed? Thanks for all the advice!
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Rod Bower - Filter??
- Thread starter dww1977
- Start date
From my notes taken from past posts (but not personally verified);
The RV-10 version used K&N RU-4250
The RV-7/8 version used K&N RU-2520.
The RV-10 version used K&N RU-4250
The RV-7/8 version used K&N RU-2520.
I don't believe these are correct. The RU-4250 has too small a flange I.D. - although the intake adapter could be modified to fit.
My Bower 6-cyl and 4-cyl inlets had K&N RU-3600 and K&N RU-2510 respectively.
I use the RU-2510 in my improved HP Aircraft Type-2 Ram-Air Intake for 4-cyl as well. For 6-cyl, I now use the RU-5059 as it is a little shorter, makes the intake assembly a little shorter.
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Use an RU-2510.
Thanks Steve
My -10 also uses the 4250 filter, FWIW.
-Marc
OK, what that means is that Rod, or someone, turned the intake adapter ring down from 4" to 3.75" so that the RU-4250 would fit on it. That filter is otherwise the same as the RU-3600 - the I.D. of the rubber flange is the only real difference.
So, for anyone with a 6-cyl. Rod Bower inlet that is unsure about which filter, just measure the diameter of your aluminum adapter ring where the rubber filter flange clamps onto it. If it is 4", get the RU-3600. If it is 3.75", get the RU-4250.
A little more history ...
At some point in Rod's history he changed from the standard body length (RU-2510) to a long body length (RU-2520) - 4 cyl. engines. The 6 cyl. engines use, as Steve has alluded to, RU-4250 (3.75" inlet diameter) & RU-3600 (4" inlet diameter), both (I believe) are still available.
HFS
Good info. Looking at the chart on K&N's site, it appears RU-2520 is no longer available. The listing on Summit's site seems to confirm.
I found a chart in the Internet Archive showing the dimensions of both the RU-2510 & RU-2520.
My 4 Cyl (RV-7) Rod Bower setup is approximately 2014 vintage. I'm not sure which filter is installed.
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Supposedly, there is still one (RU-2520) listed on eBay. Selling from AUS, with $ conversion ~ $71.00 USD. So ...
HFS
How have you guys cut the hole in the end of the filter? I thought about trying a 3" holesaw in the drill press, but I don't see that ending well. The filter is slick with oil and I don't know how I could hold it steady without damaging it.
Any effective suggestions that won't result in a lost digit?
Any effective suggestions that won't result in a lost digit?
A 3" Greenlee hole (knockout) punch does a great job creating the 3" hole in the end of the filter.
Unfortunately, in my experience, the RU-3600 was not a suitable substitute for what I assume is an RU-2520. Two issues; The inside flange diameter of both filters is 4" (green lines). But the outside flange diameter on the original is 4.25" while the outside flange diameter of the RU-3600 is 4.5" (blue lines). Outside flange diameter is not depicted on the K&N diagrams.
After a few minutes of struggle, I was able to force the RU-3600's larger diameter flange into the aluminum flange plate. It's possible the original filter has shrunk over the years but the original fits the flange plate opening perfectly while the RU-3600 could just barely be forced inside.
At this point, I thought I was home free. But alas, it was not meant to be. The overall height of the RU-3600 is about 1/4" taller than the original and no amount of forcing was going to allow the base plate to properly seat inside the canister. The short green line shows the flange plate sitting proud of the caister by about 1/4":
The RU-2520 is seemingly no longer produced and despite the searches of a few weeks ago showing only one available anywhere in the world (in Australia) , today's search showed one available on Amazon. So, I've ordered an RU-2520 and will try again later this week.
Bear in mind, it's only an assumption that RU-2520 is the original filter. There is no legible part number anywhere on the filter itself.
I
Please let us know how the RU-2520 fits. To solve the problem of the thicker flange, all you need to do is open up the hole in the aluminum back plate a little bit. A 1/2" drum sander in a dremel tool makes short work of that. I'm wondering if the apparent extra 1/4" length is the result of an internal radius on the rubber preventing the aluminum back plate from fitting all the onto the flange until it is tight against the rear face of the filter body? Opening up the hole in the aluminum back plate should help with that too. Keep us posted what you learn.
I shouldn't give away all my trade secrets I suppose, but I have a wood disc that fits inside the filter with a 1/4" hole in the center. I use this to locate a pilot hole in the center of the filter end, so the hole will be centered. then I use a hole saw, guiding with the pilot hole. I cut very slowly with moderate RPM. Haven't lost any fingers yet. I use a 2 7/8" hole saw, makes a good fit for my butterfly valve holder/flow diverter.
Yes, I considered enlarging the opening in the aluminum flange plate. But I didn't want to start modifying the housing until I was sure I needed to.
The RU-2520 is sitting on my porch. I'm traveling for a few more days.
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Great. Just ordered a backup since Amazon said they had some. Then saw your post. Wasn’t able to cancel immediately after ordering. Will report what I get.
Strike two… Ordered a RU-2520 on Amazon last week. Tried to immediately cancel after seeing the most recent post, and Amazon said I cant cancel since they were preparing for shipping. I chose no rush shipping. A RU-3600 arrived today. Sent back.
My filter is still serviceable, but not sure what route I’ll take when it needs replacement. Hoping someone comes up with a good option.
My filter is still serviceable, but not sure what route I’ll take when it needs replacement. Hoping someone comes up with a good option.
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All that is required is to enlarge the opening in the back plate to gain more clearance for the thicker rubber flange and molded corner radius.
Or, you could buy a new ram-air intake from me!
Per post 13, the length is a little longer. I seem to remember opening up the flange a few years ago when I changed it last. No problem modifying the Rod Bower. I’m just out of town for a while. Had the wrong filter returned for now.
Link for your ram air?
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As I wrote above, the opening in the back plate is not the main issue. The RU-3600 is too tall.
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That’s what I got out of your post. Thanks for clarifying. I previously opened up the flange several years ago with the last filter change. Did you come up with a solution?
For the time being, I bought the K&N cleaning/oiling kit and reused the existing RU-2520.
Hmm. That is a bit surprising, given that K&N lists them both at 5" long. I was thinking that you could drill an additional set of holes in the canister that would allow the extra length, but I can see by your picture that the back plate does not have a wide enough flange to allow that. It looks like the only way to accommodate the added length would be to make a new back plate with a wider flange, most easily from fiberglass.
