Dirt bike engine and transmission oil change

The purpose of this article is to provide general advice on changing engine and transmission oil on a dirt bike. The example here is from a 2010 KXF450.

Always refer to the owner's manual regarding your specific machine because there are differences between models and years. Follow the advice in the owner's manual regarding oil changing interval and procedures. The interval for filter and oil change recommended for the 2010 KXF450 is 15 hours of riding time.

1 It is important to change the oil as recommended for several reasons. 1) Particulate from normal engine wear can accumulate. 2) Mechanical and thermal stress on the oil causes it to lose its lubricating properties over time. 3) Oil can become contaminated due to a variety of other possible means.

2 Always start with a clean motorcycle. The underside where the drain plugs are located should also be clean. This KXF450 has two oil drain plugs. Both are required to fully drain the oil reservoir. Oil drain plugs are not always underneath as shown here, some are on the lower side of the casing. Also, this bike shares engine oil with transmission oil. They are one and the same. Other bikes separate the engine and transmission oil, such as many of the 2000 era Honda 4 strokes. Of course, two stroke oil change is transmission oil only.

3 Typical oil fill. Some models have two because of separate engine and transmission oil. This plug should be removed for oil draining. Removing it vents the crank case facilitating faster and more effective draining. Remove with care. Dirt can embed under the outer edge of the plug(s). Carefully wipe any visible dirt away from the hole.

4 After the fill plug is removed, remove the drain plugs, beginning with the small one in this example. Here's the benefit of that triangle side stand the bike came with when new. It makes draining the oil into a pan a snap. You'll find you can often drain more oil by holding the bike at different angles once the initial flow has stopped.

5 Four strokes have oil pumps, so some oil will remain when the draining stops. Cranking the engine several times discharges oil remaining in the pumping circuit.

6 After the engine is drained, remove the filter retainer bolts. Loosen the bolts in increments moving from one to the other. The filter inside is spring loaded, so doing this is a precautionary measure to keep the cover moving out evenly and in control. However, a well sealed cover will often remain seated when the bolts are removed. On this engine, there is no way to grab the cover. A thin, sharp putty knife can be used as a wedge the wiggle the cover out, moving around the seam evenly. This must be done carefully to avoid damaging the aluminum or the o-ring seal. With any luck you can just wiggle it out with your fingers. This one was simply too tight. Lightly tapping on the cover while pulling may also work. If you do need to pry it is shown here, you can insert the screws a couple of turns each to prevent the cover from flying off. Another option for a stuck cover such as this is to use a heat gun around the filter housing. Warming the housing causes the metal to expand, thus loosensing the grip on the cover. Protective gloves will be needed if a heat gun is used.

Note: My advice here on removing a cover that is tight or stuck assumes the design to be as seen here, which is prevalent. In this example, the cover seal insets into the inside diameter of the housing. Some may exist that are face sealed only, by means of gasket or o-ring. In these cases, heating will produce no value.

7 The filter spring is on the back side of the filter. You can see that the filter has moved outward. The depth of the filter cover indicates how far the filter moved. Notice how delicate the filter housing is.

8 Expect the unexpected. These o-rings are bad because they have expanded. There is no way to insert the cover using these. o-rings such as these can sometimes be repaired if they are not knicked or torn. Refer to my o-ring repair article.

9 The filter slides right out. On some bikes, the spring will be loose and will fall or come out with the filter. This KXF450 housing has a spring retainer molded into the casting that holds the spring. Take the time to clean the housing while being careful not to get anything in the oil ports. WD-40 works great as a cleaner.

10 The KXF filter housing design is very good, making filter installation easy. The new filter is held securely on the filter cover and the spring is held in place inside the housing. Some bike models require some finess because these design features are not present. Before inserting the filter and cover, make sure the o-rings have a light film of grease. If you do not have grease, rub motor oil on them. Also pay careful attention to orientation of the cover. Passages in the cover, if they exist, must align perfectly to the housing ports. On some bikes it is possible to mount the filter cover incorrectly, so beware.

11 You will need to push against the spring while starting the screws. Always turn each screw in small increments, moving from one to the other. This is to keep the filter cover moving evenly. Never tighten only one bolt. Doing so can bind the cover, possibly even damage it.

12 Clean and inspect the drain plug(s) and fill cap(s). Make sure o-rings and-or sealing washers are in good shape. Replace as necessary. Install the drain plug(s).

13 For engine cases with sight glasses, the proper oil level is midway in the glass. Others have oil plugs installed where the oil level should be. Where there is an oil level hole but no sight glass, the oil level is correct at a point where the oil begins to run out. Checking oil level must be done with the motorcycle sitting level.

Initially, fill the oil to the low portion of the sight glass. Where there is only a plug, fill to a point near but below the hole. Lightly install fill plug(s), then run the engine at idle for a bit (10 to 15 seconds should be plenty). Shut the engine off and let it sit for several minutes. Now adjust the oil level(s) as needed.

Why do this? On systems having engine oil pumps, filling the case with oil will not fill the oil pump cavities. To what extent depends on engine design. Running the engine gets the oil pumping, thus filling those unreachable cavities. In the case of transmission oil only, doing this may have little effect on the initial level. Still, doing this is always advisable.


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