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Tech & How-to



Everyone knows K&N makes air filter elements that pass more air than the stock H-D ones do, which means more horsepower. But did you know that it also makes great air cleaner housings?

Case in point is the made-in-the-US chrome beauty we bolt onto a rubber-mounted Sportster in the accompanying photos. Named simply the #RK-3929 ($339.95), this unit fits 2004-07 Sportsters, both 883s and 1200s. This oversized custom cleaner housing was designed to fit around one of K&N’s high-flow filter elements. The intended buyer is a Sportster owner who wants to increase air flow to his engine to reap additional power, which comes partly due to the increase in filter element surface area.

The #RK-3929 consists of a powdercoated, billet-aluminum backing plate, internal breathers, and a built-in, dyno-tuned velocity stack to smooth out the air stream as it enters the engine’s intake tract. Of course, a K&N high-flow washable and reusable “lifetime” filter is also in the box. That means, as with all K&N elements, the service interval between cleanings is much longer. However, there is no new outer cover, since this setup is designed to reuse the stock outer cover. The best part is that though we put the bike onto the dyno after installation, you don’t have to since no fuel setting modifications are necessary. This installation, which reaped 4 more horsepower, can truly be completely done in your own garage.

–Chris Maida as published in American Iron Magazine, the world’s best selling Harley magazine.

• Torque wrench (in-lbs.)
• Ratchet
• Red Loctite
• Blue Loctite
• 5/16″ wrench
• 5/8″ wrench
• 5/32″ Allen
• 3/16″ Allen
• 14mm deep socket

K&N Engineering
1455 Citrus St., Dept. AIM
Riverside, CA 92507

Marquee Customs & Classics
72 Siemon St., Dept. AIM
Bridgeport, CT 06605

Rob’s Dyno Service
Dept. AIM
Gardener, MA 01440
http:// www.RobsDyno.com

1 Our opening shot shows a 2007 1200 Sportster fitted with SE slip-on mufflers up on Mark’s lift. Its air cleaner and throttle body support are removed, so it’s ready to receive a new K&N assembly.

2 Mark starts the installation by slipping a K&N-supplied washer over each K&N breather bolt extension.

3 Mark uses a little red Loctite and a 5/8" wrench to screw a K&N breather bolt extension into each head. He then torques the extensions to the stock spec of 120-144 in-lbs.

4 Mark then secures the four K&N spacers (standoffs) in the K&N backing plate using a 5/16" wrench, a 5/32" Allen, and a little blue Loctite.

5  The rubber K&N internal velocity stack can now go on. Mark slips it inside the backing plate after making sure the notch in the stack lines up with the breather hole in the backing plate.

5 The rubber K&N internal velocity stack can now go on. Mark slips it inside the backing plate after making sure the notch in the stack lines up with the breather hole in the backing plate.

6 Mark then inserts the three K&N-supplied Allen bolts into the backing plate, alongside the velocity stack. Mark uses a 5/32" Allen to push each bolt through its tab on the velocity stack.

7 With the stock gasket on the back of the backing plate and over the three bolts he just put in, Mark attaches the plate onto the throttle body using a 5/32" Allen and some blue Loctite.

8 The stock breather bolts (minus O-rings) with the stock washer and a little blue Loctite, go into the K&N breather bolt extensions. Mark uses a 14mm deep socket to torque them to 120-144 in-lbs.

9 Mark can now position the filter element over the backing plate. As he does this, he makes sure the element is fully inside the plate’s outer lip.

10 The two spacer cushion assemblies are installed onto the filter, using the K&N-supplied hardware, some blue Loctite, and 5/32" Allen. These bolts, which also secure the filter element, get torqued to 40-60 in-lbs.

11 The stock outer cleaner cover and insert, minus the rubber gasket, gets reinstalled using the stock bolts, some blue Loctite, and a 3/16" Allen. He torques the bolts to 36-60 in-lbs. AIM


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