How to Change
A 2 Stroke Dirt Bike's Gear Oil

This article covering how to change a 2 stroke dirt bike's gear oil will detail exactly how to perform an inexpensive maintenance procedure which anyone whom rides, or maintains a 2 stroke dirt bike can easily perform themselves, and with the tips below, you'll find that changing the oil in a 2 stroke's gear box (which should be done every couple hours of riding time) is probably the easiest maintenance task you can perform on a dirt bike, and if you've been taking it to someone else for oil changes, you'll probably realize that a 2 stroke dirt bike is one of the simplest, and easiest dirt bikes there are to maintain.

Keeping fresh oil in the transmission can keep a dirt bike shifting smoothly, and going through the gears effortlessly while hopefully even minimizing the false neutrals and increasing the life of the transmission or clutch, but if the dirt bike is still nasty from the last ride, or day at the track, it's advised to wash the dirt bike beforehand, as this should always be done After each ride vs before, and having a clean motorcycle should always come before any type of maintenance.

How to Change A 2 Stroke Dirt Bike's
Transmission Oil

Picture of the Engine Oil Draining on a 2 Stroke Dirt Bike
  • If the dirt bike has been sitting for a while, such as in the trailer or garage overnite, you should fire the dirt bike up for a few minutes to get the gear oil warmed up to the point where the clutch cover is warm to touch, as the oil will drain better while warm with greater ability to remove contaminants and metal particles within the oil.

    Note: While the motorcycle is running, disengage & re-engage the clutch a few times by squeezing the clutch lever to the bars and releasing it, as this will move oil through the clutch and enable more of the used / contaminated oil to get out of the gearbox so more fresh oil can go in.
  • After running the dirt bike until warm, shut it off and lean the bike up against the wall, truck or whatever's nearby so that it's sitting level.
If you use one of the triangle stands that come with most new dirt bikes, Remember that these leave the bike leaned over which results in a large amount of oil pooling inside the case halves or covers, so it will be necessary to hold the bike upright at some point to enable removal of all the oil.
  • Next, with a closed top oil drain pan that enables you to inspect the oil as it's drained such as the one pictured above, place this under the motorcycle, then using the proper size deep well socket, or socket with an extension and ratchet, loosen the oil drain which will likely be the only 14mm or 17mm hex head at the bottom of the engine although once the drain plug is broke loose, it's best to ditch the ratchet, then using only the deep well socket, (or socket with the extension attached), unthread and quickly remove the drain plug and If done quickly & carefully, you'll learn that this can be accomplished without getting oil all over your hand, the socket, or everywhere else, although accomplishing this may take some practice.
  • Regardless of which method you use to keep the dirt bike upright, once the oil starts draining, it's important to grab the dirt bike and hold it so it is perfectly upright, as the dirt bike will be leaning to one side if it's leaning against a wall, or is held up via a triangle stand and all the oil will not be able to drain, as it will pool up in areas such as inside the clutch cover, although this is easily remedied by a recommended practice of standing the bike upright and removing the pooled oil by slightly leaning / swaying the bike from side to side to facilitate complete draining.

If the Motorcycle has a Skid Plate Under the Motor

Picture of Engine Oil Drain Seen through Skid Plate Access Hole Fortunately most skid plates have an access hole to allow for draining of the transmission oil without requiring removal of the skid plate each time, and this does make changing the oil much easier, although once the oil draining slows, you'll find that it can often make a mess, as the oil will frequently start running onto the skid plate vs running straight down through the hole in the skid plate which generally results in a mess that will need to be cleaned up, but the easiest way of doing this is with a commonly available brake parts cleaner which can be obtained at any auto parts store, and most any brand of "brake clean" works well without leaving any oily residue behind.

Once the Transmission Oil has Finished Draining

Once all the oil is out and provided that the OEM plug was not magnetic, or if there was not a magnetic oil drain plug installed previously, It is strongly recommended to use a Magnetic Oil Drain Plug in place of the stock / OEM oil drain plug, so if you don't already have one, you should definitely do your transmission a favor and order one of these.

Picture of a Magnetic Oil Drain Plug with Metal Shavings Attached to Magnet

A magnetic oil drain plug is inexpensive and a great investment that even the most casual rider should use, as the gears in the transmission are straight cut and create metal particles even during casual riding, although if you're the type of rider who's banging gears, hitting false neutrals, and just all around hammering on the transmission, you'll be surprised at the amount of metal clung to the magnet at each oil change, so a magnetic oil drain plug is a must, and if you don't yet have one, you should order a magnetic drain plug so you will have this ready to install at the next oil change.

Now ensure the drain plug is clean and if magnetic that the magnet is cleared of any metal particles, then replace the drain plug and tighten it snugly. ("Snugly" is about 20 lb ft of Torque)

A Warning Against Over-Tightening: When tightening the oil drain, use care to not over tighten the drain as doing so could result in pulled threads (when the oil drain gets loose suddenly, or on used bikes when the plug will not tighten) as at this point the threads in the case are usually pulled out (the threads or what appears as aluminum may be wrapped around the threads of the plug) you'll be needing to put a Heli-Coil in the hole, but it's not entirely bad as you'll be able to find some help with this elsewhere on our article detailing how to repair damaged threads.

How to Properly Refill the Gear Oil

Regarding ATF
Lower Oil Levels

Some people may tell you their tips regarding the use of ATF or running lower oil levels.

These tips are valid but generally only reserved for those whom are interested in extracting the maximum performance from the bike, and although running ATF in the gear box does result in a smooth clutch and minimal drag on the transmission, you'll be needing to change the oil after every ride if using ATF.
Picture of Pouring Engine Oil
  • With the oil drain plug installed and tightened securely and using the proper weight of oil as specified in a factory service manual specific to the bike, rotate the engine until the clutch plates are visible through the filler hole, then begin to fill the transmission with fresh gear oil.
The proper level can be determined by looking through a sight glass, by removing an oil level check bolt, and / or by filling the engine with the quantity that's generally cast into the engine's side cover. (e.g. 850cm marking)
  • Once the approximate quantity of oil has been poured into the transmission and the oil is either visible in the sight window, or it has begun to run out through the oil check bolt, you'll need to replace the oil check bolt and fill plug, then fire the bike up and allow it to run for a few seconds to move the oil throughout the transmission, then shut the motorcycle off and recheck the oil level.
  • If the dirt bike you're working on does not have a sight glass, remove the oil check bolt and top off the oil level with the same motor oil you had been using until the oil is either level in the sight glass, or it begins to seep out of this oil check.
  • Once full, install the fill plug and the oil check bolt, tightening the check bolt securely while using extreme care to not over tighten this, as oil check bolts are easily and frequently over tightened resulting in pulled threads, which generally requires removal of the right side engine cover to repair properly, as it is otherwise impossible to remove the tang which will break off from the Heli-Coil insert after installation, but more on this can be found in the article on repairing damaged threads.
If the clutch is slipping, Be Sure to Check Out Our:
Article on Clutch Maintenance and Service

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