"Tech Tip" air filter maintenance

Discussion in 'Technical Posts' started by Pete Payne, Dec 11, 2001.

  1. Pete Payne

    Pete Payne Member DRN Member

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    This is for all foam air filters.

    Ok , this might be a boring subject, but it is a very important one.
    It amazes me the number of bikes that are brought into my shop with this one complaint " it feels down on power, I recently replaced the topend . What could be wrong ? " First a quick compression check, sometimes all you have to do is lay a finger on the kickstarter and it will fall down. Off come the seat and out with the air filter. And there it is -- a layer of dust inside the air boot. It only takes a little of this dust to get by and the rings or worse are wiped out. Think about this -- most 125's peak out at around 11,000 RPM ( revolutions per minute) so let's see , this piston is going up and down 11,000 times a minute . WOW , that is 183 times a second. Now lets mix in the dust / dirt going past the piston and rings, not to mention the crank. It is kind of like an orbital sander going to town in there.

    So how do we avoid this? Lets assume the air filter is dirty and not a new one. If you have used a petroleum based oil like bel-ray air filter oil you should start with a solvent based cleaner , something like Safety Klean or kerosene. Make sure you USE rubber gloves that are solvent proof and are working in a well ventilated area . Wash the filter in this one or two times and try to wash the filter from the inside out . This will push the oil and dirt out of the filter instead of thru it were sometimes small grains of sand will get stuck and are almost impossible to bet out (this is a time bomb waiting to get pulled thru the air filter and wreak damage on your engine).
    Next wash the filter in some warm water and some fairly strong liquid/powdered detergent. and finish with a final rinse of water only .The soap will remove the lighter based oil were as the solvent will thin out the thicker air filter oil and remove most of the dirt and oil. You should do both steps. If you only use the solvent --- the filter will not properly dry. So when you reapply the new air filter oil it will thin it out and make it less tacky.

    Now that the air filter has been cleaned with both steps let it completely dry. Now apply the new oil . you will only need 2-3 ounces of oil to properly oil the filter . This should be worked completely through the filter and have an even appearance any area's not covered with oil should be treated. I like to do this by putting the area that needs to be spot treated on top of the bottle and blot the filter with the oil . Then work it through.

    It is also a good idea to let the filters for a good 15-20 minutes before reinstalling it into the bike. Many of the oils have a product in it that will evaporate after the oil is applies . This allows the oil to be thinner right when applied and lets it work in easier and then it will evaporate and get thicker/ tackier .



    Some people use a little grease on the rim of the filter. I personally do not use any.The rim is treated with the same oil as the rest of the filter. And have not had any problems in 27 years of riding. If you tighten the air filter down properly and the rim is seated good -- you won't have a problem here .

    Now if you use the no - toil air filter oil and cleaner you do not have to use the solvent (their oil is not petroleum based). You just use their cleaner with the water , a good complete dry down and go from their. Also you do not have to worry about all the toxic chemicals and the fire / explosion danger.

    Also take the time to use a flash light and look down into the air filter boot to make sure their is not ANY specs of dirt in their. You should be able to eat off of it. The same goes for the air filter cage. Also clean the air filter box. This should be done on a regular basis also.

    As for the guy with the engine problem . We will have to do a complete tear down and inspect the engine and clean the carb. and reeds. There are a lot of bad places for that dirt to get into , and we don't want to do that --- do we !!!
  2. Jaybird

    Jaybird Apprentice Goon

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    Pete,
    Any thoughts on the "over-oiling" of a filter?
  3. vznx1w

    vznx1w Rookie DRN Member

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    I believe its impossible to overoil the filter--as long as you give it a good squeeze to remove the excess prior to installation. Of course, it is possible to waste oil by applying an excessive amount and then squeezing it out. However, when judging how much oil to apply keep the appropriate risks in mind: if you overoil you waste a few ounces of oil, if you UNDEROIL you waste your ENGINE--quickly.

    I have a friend who just doesn't get this. He insists on using minimum oil hoping for more horsepower. In the last two seasons he has gone through numerous pistons, two cylinders and two crankshafts. His 2001 CR250R needed a piston at 8 hours and then wore the replacement so badly the skirt cracked. This guy is a working Dad and doesn't ride all that often or hard, yet his bike usually runs bad, because the topend is constantly wornout. The last time we rode together he couldn't do the big jumps because his bike was running and sounding like a clapped-out 1978 Suzuki PE175 and didn't have enough hit to get into the air. After that ride he quit riding for the season because he couldn't afford the repairs.

    Moral: Use the oil and plenty of it.

    Tip: I like to oil the filter inside a gallon size ziplock bag. Then I can squeeze the oil around to thoroughly saturate the foam with minimum oil wastage.

    Steve
  4. RM_guy

    RM_guy Scared of DirtWeek<BR>Club ********* Damn Yankees

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    Too much oil left on the filter is a problem. Put a lot on the filter so you know it is fully covered but squeeze out as much as you can or you will be blocking air flow and choking the engine. You can't squeeze out too much oil.
  5. vznx1w

    vznx1w Rookie DRN Member

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    I agree with RM_Guy that you can't squeeze out too much oil. Globs of liquid oil in the filter is not a good thing.

    My previous tious post was emphasizing that you don't want any arears of your filter to be dry and/or oiled insufficiently to trap dirt properly and that if you get the filter too "wet" you can simple squeeze out the excess.
  6. Jaybird

    Jaybird Apprentice Goon

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    I may be wrong, but I've always believed that an over oiled filter can cause jetting problems. Makes sense, yes?
  7. brett r

    brett r Rookie DRN Member

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    Can you use motor oil on the filter
  8. RM_guy

    RM_guy Scared of DirtWeek<BR>Club ********* Damn Yankees

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    Before the advent of the tacky filter oils, motor oil was all that was available. The filter elements were also different. The pores in the foam weren’t as large as they are today so motor oil worked OK for trapping dirt. IMO, newer filters have larger pores for better airflow but they need the tackiness of the newer oils to properly trap dirt to keep it from getting into your engine.

    Also, motor oil tends to “sink” to the lower portion of the filter overtime. In any case, with all other things being equal, air filter oil will stop more dirt just because it is stickier.

    It’s well worth the extra money to protect your engine. A rebuild is much more costly.
  9. RM_guy

    RM_guy Scared of DirtWeek<BR>Club ********* Damn Yankees

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    Makes sense to me. It's like running with a clogged filter or with the choke on.
  10. spanky250

    spanky250 Mod Ban

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    The biggest problem that I have seen with over-oiling a filter is the excess oil runs into the airboot and gets sucked into the small air passages in the bell of the carb, clogging them and wrecking the off-idle jetting and response. One the other hand, as long as you don't have oil dripping off of the filter or running out of it, you can't put too much oil on it.
  11. Pete Payne

    Pete Payne Member DRN Member

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    You guys have got it right. An over oiled air filter will make it seem like the choke is on and mess with jetting.
    No do not use motor oil it is way too thin and not even close to being tacky enough.
  12. 99cr250

    99cr250 Rookie DRN Member

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    I change my air filter every ride. I put 100+ hours on the same top end with no decline of power. I thought it would be time to change it any way. I took it to the Honda shop to get the cylinder honed and they said i was just wasting my time changing the top end. It didn't need to be changed.
  13. Pete Payne

    Pete Payne Member DRN Member

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    99cr250, Thats the point. It is very important to not only service your air filter frquently but properly. It makes your bike and $$$$ go a long way.
  14. whyzee

    whyzee Never enough time !

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    Get this,
    I'm cleaning a filter I’ve have about 4 weeks now, it's a Yamaha filter, and the glue breaks down and the panels come apart. I cleaned it as I cleaned my other filter, which lasted a year. Liquid detergent and warm water. I'm pissed, going to take it back to Yamaha and use a twin air again. Anybody else run into this?

    Dave:eek:
  15. dale williams

    dale williams Rookie DRN Member

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    I hear that if you switch from No Toil to petroleum or the other way that the glue will come apart.
    Also if you over oil the filter the oil will line the inside of the air boot resulting in a slightly sticky finish. This is of no consequence but can be used to indicate if dirt is getting by because it will catch on the boot wall.
    Also a good clean air filter can result in a long life for a 2 stroke. 2 stroke engines are used in some very light airplanes and they are getting something like 1000 hours or better on a top end.
  16. FNINJA

    FNINJA Rookie DRN Member

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    K&N air filter oil

    Is it ok to use K&N airfilterl oil spray on a dirtbike filter, I have it for my street bikes.
  17. eunos

    eunos Rookie DRN Member

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    Some thoughts on filters, during the moto-x season we change the filter after every race and practice, thats 4 times per day, we have never experienced any abnormal wear patterns. We apply oil by submerging the filter after cleaning and then squeezing out the excess and leaving to dry for at least 2 days, clean filters are then stored in zip bags to maintain the tackiness.
    We figure oil is cheaper than pistons!

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