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R/C Tips and Tricks - Nitro Engine Air Filters

If you run nitro, you need an air filter. No surprise there! But to make it function properly and protect your engine, it needs to be clean and oiled, and you need to make sure it's installed properly so no unfiltered air (or dirt!) can get past the filtering media. There are many types of filters out there, this is only a sample:

Filter Design: Which to choose? I strongly recommend the "buggy-style" filter (top-left image above) that has a base cap with protruding center structure around which the cylindrical element is positioned, along with a simple plastic cap that uses a screw through its center to secure it to the protruding center section of the base. Simple, cheap, effective, and nearly universal. Easy to find replacement elements for them, too.

DO NOT USE this style! Putting a shield over the element seems logical, since that shield can prevent flying debris from hitting the filter and it sheds water nicely, keeping it from entering the engine. However, how dirty is the element? You'll have no idea unless you remove the cap. What if you're used to running four tanks through your engine before cleaning the filter, but you happen across some unusually-dusty terrain? Maybe it'll occur to you to check your filter more often than usual, but maybe it won't. If you have an exposed filter, you'll easily see when the foam is dirty and in need of replacement.

I ran that style filter on my buggy for a couple tanks on a dusty track. It started running poorly, but I couldn't figure out why. I tried another tank, but it got worse. This is what I found:

The filter got filthy, but the oxygen-hungry engine kept sucking in air, so the dirty, dusty air went in via the path of least resistance, which was between the element and the cap. Thus, unfiltered air got into the engine. A lot of it! It coated the inside of the air filter neck and the carburetor as well. Fortunately a cylinder pinch restored much of this engine's former glory, but its overall longevity was greatly compromised.

Installation: No matter what design you use, make sure it's fastened tightly to the carburetor and the neck! Use strong cable ties and pull them very tight, or even consider using a small automotive worm-gear hose clamp as demonstrated here by Saxy from the RCBasher message board:

Cleaning: This isn't difficult, but it IS important. I just use several drops of Dawn diswashing liquid and lots of water to clean and flush the filter element. It's best to try to work the dirt towards the outside of the filter if possible, but that's easier said than done, since squeezing the element is about the only way to work the soap and water into the foam to do the necessary cleaning. Keep washing it, using additional soap as necessary until the soap suds you rinse off are still clean, meaning no more dirt is coming out.

Oiling: If you've got a new (or freshly cleaned) filter, an easy and "clean" oiling method is to throw the filter in a plastic Ziploc^TM bag, drizzle some filter oil inside the bag, zip it closed, and start kneading it to work the oil into every pore of the filter foam. If you still have white or clean spots once the oil is used up, add more and keep working it until the foam is uniformly covered and colored. Then remove it from the bag, wrap it in a paper towel, and squeeze or blot as much oil out of it as you can. Keep moving it to clean spots on the paper towel until you further squeezing extracts little additional oil. This allows the filter to still "breathe", but it'll retain enough of the sticky oil to filter properly.

Installation: Installation is simple, just make sure the element is properly seated in the plastic housing and no edges are caught or hung up on something. Make sure the screw holding the end cap in place is snug, and if the center portion (the part the end cap screw threads into) of your filter housing is metal, be sure to use threadlock on it! I once lost a filter and thus a nearly-new engine because I didn't threadlock that screw.

Pre-Filters: I do recommend the use of pre-filters for a couple reasons. First, there's more filtering media for the dirt and dust to penetrate before causing damage. Second, since a pre-filter goes around the regular filter, it has to be larger in diameter, which means more filter surface area which means it'll take longer before it gets clogged. Third, it really prolongs the life of the main filter since the pre-filter catches most of the dirt. And fourth, the pre-filter is very easy to remove and replace, so you're more likely to keep your stuff clean. Let's be honest, if maintenance is a pain, we put it off as long as possible. If it's easy, chances are we'll keep to a good schedule! Use a pre-filter.

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