Periodic Cleaning of the Wet-type Air Cleaner Element is a Must to Keep it in Good Condition!

The air cleaner is an essential part that feeds clean air to the engine. The wet type air cleaner element, which is often used in off-road models, small motorcycles, and out-of-print motorcycles, can keep the intake air clean for a long time by cleaning it regularly. It's easy to do, so if you're wondering when you've cleaned your air cleaner element, you should definitely give it a try.

Sponge type is a minority compared to paper elements

The air cleaner element of Yamaha SR400 in the carburetor era is wet sponge type. By loosening the thumbscrew on the surface of the sponge, the frame and sponge can be removed as one piece. Due to the characteristic of the air cleaner box, it is easy to absorb dust and dirt because of the large negative pressure inside the box, so the air cleaner element is very important. Even if there is a box, if there is no element, there is not much difference from a straight carburetor with only a funnel.

Up until the mid-1980s, racers used to use only air funnels and no air cleaner box, but after the use of ram pressure to boost the engine using driving wind, even carburetors started to have air cleaner boxes. Since the switch to fuel injection (FI), the air cleaner box has become a necessity.

If we look at the element inside the air cleaner box, we can classify it into two types: the wet sponge type and the dry paper type. The former is made of polyurethane, while the latter is made of non-woven fabric. Both have the same purpose of protecting the engine by absorbing dust and dirt in the air. It is also said that there is no clear difference in performance as long as proper maintenance is performed.

Most of the motorcycles on the market today are equipped with a paper-type cartridge filter. There are two types of paper type filters: dry type and viscous type that is soaked with filter oil. As for the sponge filter, it was installed mainly on scooters and out-of-print motorcycles in the 2-stroke era.

The reason for the high adoption rate of the sponge type, mainly in small displacement vehicles, is that it is more compact and less expensive to manufacture than cartridge filters. The cartridge type requires a frame to hold the air cleaner element which is made of non-woven fabric bent into a bellows shape. Sponge filters also require a frame, but by relying on the flexible nature of the sponge itself, the air cleaner function can be achieved even with a simpler frame than the cartridge type.

On the other hand, in the category of motorcycles, on-road models shifted to the paper type quickly, while off-road models used the sponge type for a relatively long time. The reason for this is that the sponge type was more advantageous in terms of cleaning. Compared to on-road models, off-road models' air cleaner boxes are likely to be exposed to more dust, mud, and even water.

However, most small-displacement vehicles and off-road models are now paper type, and sponge type air cleaner elements are in the minority.

The air cleaner element of SR400 can be divided into resin frame and sponge, and the sponge can be cleaned by itself. If the sponge is damaged or deteriorated, it can be purchased separately. It is understandable that you want to remove the air cleaner box for customization, but in that case, you should install the air filter.
 

Be careful not to choose the wrong cleaner or you'll end up with a wreck.

Since 2010 model year when the fuel system was changed to fuel injection (FI), the air cleaner element of SR400 is paper type. This type cannot be cleaned and should be replaced every 20,000km.

The only maintenance for the dry type air cleaner element is to replace it according to the mileage. If there is dust or dirt in the folds of the element, you can tap it on the floor to remove it, or blow it off with a light air blow from the engine side. Check the service manual to see if your motorcycle has a dry or viscous element.

The sponge type also has nothing special to do up to the regular inspection distance, but when the time comes, it can be refreshed by cleaning instead of replacement.

The Yamaha SR400 shown here is equipped with a sponge filter until the 2008 model when it was a carburetor model, and the FI model after 2010 has a paper filter. The first model was introduced in 1978, so sponge filters were common in that era. The SR was originally developed as an on-road model based on the XT500 off-road model, which may be the reason for the sponge filter.

The reason why sponge filters are called wet filters is that the sponge is soaked with filter oil. Therefore, when maintaining a sponge filter that is dirty with dust and dirt, new filter oil is applied, but it needs to be cleaned beforehand.

Some people spray new oil on top of old chain oil when maintaining their drive chain, but simply applying a layer of filter oil is not effective. Simply applying a layer of filter oil over the old chain oil will not do the trick; it will only seal in the dirt that has already accumulated.

To clean the sponge filter, use clean kerosene or a special filter cleaner. You can also clean it with hot water and kitchen detergent, but filter oil is more viscous and stubborn than salad oil, so it takes more time to clean. In this respect, kerosene and filter oil are superior in their ability to dissolve oil.

Another disadvantage of using a sponge with water is that it takes a long time to dry. If you have time to let it dry for several days, it is good, but if you want to restore it by applying filter oil immediately after cleaning, it is better to clean it by other means than water.

However, depending on the compatibility between the type of solvent contained in the cleaner and the material of the sponge, the sponge may become brittle. Also, depending on the material of the urethane foam, which is the material of the sponge filter, a reaction called hydrolysis may occur when moisture in the air comes into contact with it, causing the sponge to crumble into pieces, so it is important to touch the sponge to check if it has been used for too long even if the mileage is short.

Place the air cleaner element and filter cleaner in a plastic bag and rinse. This is less wasteful than pouring and the cleaner is easy to collect after washing. If the filter is too dirty to be washed at one time, replace the bag and wash multiple times.

If you squeeze it like a rag, it may cut or tear, so handle it carefully. After cleaning, press the rag against the cleaner and absorb it. The instruction manual for Yamalube filter oil instructs to let the cleaner dry completely, so dry it thoroughly while changing the rag.

Restore performance by gently rubbing and applying filter oil.

There are a variety of filter oils available, but products developed by motorcycle manufacturers offer a sense of security. You can choose your favorite brand, but Yamalube's oils and chemicals have a high cost-performance ratio.

Infiltrate filter oil into a completely dry air cleaner element. As with the filter cleaner, put the oil and element in a plastic bag and rub it in to prevent wasting the oil. After the oil has been spread over the entire area, wipe it off with a rag until it blots slightly when you press the sponge to restore it.

The instruction manual of Yamaha SR400 of the carburetor era states that the air cleaner element should be cleaned with clean kerosene. The use of gasoline or highly flammable cleaning agents is prohibited.

Here we use a special cleaner for sponge filters, but to avoid wasting it, put the cleaner in a plastic bag or can and rub the element in it. If the filter is too dirty to be cleaned in one pass, replace the cleaner and wash it twice.

After cleaning, press a clean rag to soak up the cleaner or squeeze it lightly by hand. Gently handle a long used sponge as it may tear if squeezed too hard. Some people may think that using a compressor to blow air is better, but air blow guns are useful for targeting a small area, but they are not efficient for blowing the cleaner all over the filter, even though it takes time. It is best to use a rag or towel to absorb the cleaner.

Filter oil must be able to catch dust and debris while not resisting the air intake. If you over-soak the filter oil to get rid of the dust, there is a possibility that the mist of filter oil will enter the combustion chamber. Unlike 2-stroke engine oil, filter oil is not a combustion oil, so if it sticks to the combustion chamber or spark plug, it may remain as carbon.

Yamalube filter oils are designed for use in motocross racing and feature performance that prevents clogging and emulsification even when sand, mud, and water are mixed in.

After cleaning the filter with the cleaner, let the oil penetrate into the completely dry filter. As with cleaning, pour the oil onto the filter in a plastic bag and rub it well inside the bag to ensure even penetration throughout. Once the oil has soaked in, press it with a rag to remove excess oil. If too much is absorbed, the ability to absorb dust and debris will be reduced, so leave enough oil to lightly blot when pressing the sponge.

If this restores it to the inside of the air cleaner box, cleaning is finished. However, since the inside of the air cleaner box is oily and dust and dirt often adhere to it compared to the paper type due to the filter oil, it should be cleaned with parts cleaner.

When you cut out a generic sponge filter to use as an air cleaner for your intake system customization, you will also often need to clean and apply filter oil, so it's good to remember this procedure and key points.

If the amount of filter oil applied is too much, oil mist may adhere to the inside of the air cleaner box. Before installing the air cleaner element, let's clean it with parts cleaner.