The drain bolt gasket (drain washer) is always recommended to be replaced when changing the engine oil. The drain gasket provides sealing performance by collapsing on itself, but depending on the condition of the engine and bolt seating surface and the type of oil used, oil seepage may occur slowly. In such cases, changing the type of gasket may stop the oil seepage.
Engine oil that may leak or seep even if the threads are not damaged
When the drain bolt is moist with engine oil and wet with oil, although not to the point of leakage, suspect a faulty oil drain gasket. If the drain bolt is struck against a rocky surface when driving a trail vehicle on a forest road, the impact may cause a crack in the crankcase, and in such a case, it will not be a simple job of replacing the gasket. As an aside, the protrusion on the crankcase in front of the oil drain bolt serves as a guard to prevent direct hits from bouncing rocks while driving.
When engine oil seeps out even after tightening the drain bolt, not only replace the gasket but also check the condition of the engine side and the drain bolt's tightening seat surface. If the drain gasket has a habit of being over-tightened with excessive torque, the crankcase may have a tightening mark along the outside diameter of the gasket, and engine oil may seep through the tightening mark.
If there are linear marks on the crankcase gasket seating surface, smooth them out with an oil stone. If the oil stone hits the crankcase gasket at an angle, oil leakage may become worse. If aftermarket aluminum drain bolts are used, check the condition of the bolt's seat surface.
The gasket (drain washer) on the oil drain bolt is specified to be replaced with a new one after one use. This is because the gasket is crushed when the drain bolt is tightened to provide sealing performance. The oil drain hole on the engine side and the seating surface of the drain bolt are machined with flat surfaces, but they are not perfect.
The gasket prevents engine oil leakage by absorbing slight surface irregularities and inclination of the mating surfaces. However, once the drain bolt is tightened and the gasket is crushed, the crushed gasket will have a crushing habit that follows the surface of the crankcase and drain bolt. Therefore, if a crushed gasket is reused, sealing performance will deteriorate, and at the same time, the position of the gasket in relation to the engine and bolts will change, which may cause oil seepage or leakage.
There are two types of drain gaskets: one is a punched flat plate and the other is a complex folded type. The latter type is sometimes called the crush type, and when the bolt is tightened, the folded part is crushed to improve sealing performance. However, once a bolt is crushed, it cannot be crushed any further, so care must be taken when reusing it, as it tends to be tightened with more torque than the first time, which can cause damage to the screw.
On the other hand, a symptom often seen in discontinued and old motorcycles is that oil seeps out even after replacing the gasket with a new one and tightening the drain bolt. This is often caused by poor condition of the bolt seating surface on the engine side, or damage to the threads from repeatedly attaching and detaching the drain bolt.
If the female threads on the engine side have been lacerated due to a work mistake, a new female thread must be made by recoiling, etc. Although tightening torque is applied to the bolt, the threads may be damaged. Also, if the drain bolt is rattled when installed, it will be difficult to apply sufficient tightening torque, which may lead to insufficient pressure on the gasket, causing oil to seep into the area around the drain bolt.
The engine oil used can affect the tendency to seep or leak. If you use 100% synthetic oil in a discontinued motorcycle, you may hear that seepage from seals and gaskets tends to occur more easily. The high permeability itself is a strength that allows the oil film to be retained even in areas with small clearances, but in discontinued motorcycles, this may lead to oil seepage.
Some synthetic oils also contain ingredients that can cause old oil seals and gaskets to swell and shrink, which can cause seepage, but they can also flow out of the drain gasket through the threads where the gapping has increased.
- Point 1: The gasket on the oil drain bolt is crushed to provide sealing performance, so replace it with a new one after one use.
- Point 2: If the drain bolt is repeatedly attached and removed or tightened with excessive torque, the female thread on the engine side may be damaged, causing oil to seep out easily.
Coated drain gasket popular for automotive use
This drain bolt gasket made by Daytona uses a black layer of anti-stick coating on the surface to prevent galling, an asbestos-free compound underneath, and an aluminum plate as the core material underneath. The response to the tool when tightening is softer than aluminum or copper gaskets, and you can feel the coating part being crushed.
Daytona gaskets sold in two specifications: 3-packs and 10-packs. Inner diameter = 4 sizes for drain bolt diameters of M8, M10, M12, and M14.
This drain bolt used an aftermarket copper gasket that was smaller than the OEM gasket with an outside diameter of 22 mm. Using a smaller O.D. size than the factory gasket can cause it to cut into the seating surface on the engine side and cause scratches. The outer diameter of the Daytona gasket is 21mm, which is the same size as the factory gasket.
The standard flat gasket materials are copper or aluminum, which are soft enough to follow the surface shape of the mating surface.
The Daytona drain bolt gasket introduced here is made of three layers of aluminum material with asbestos-free compound and antistick coating, and features two layers that are softer than metal and adhere to the engine and drain bolt surfaces to provide high sealing performance by following uneven surfaces. This is a feature of this product. In addition, Daytona also sells rubber-coated drain gaskets, both of which have been well received for their effectiveness in preventing oil seepage from the engines of discontinued and older vehicles.
The three-layer gasket comes in four sizes for M8, M10, M12, and M14, and can be used not only for motorcycles but also for automobile oil drain bolts if the drain bolt diameter matches. Although the coating type drain gasket was originally popularized for automotive use, many people use it for automotive use since it is readily available at motorcycle accessory stores.
Oil drain gaskets are inexpensive parts, even the coated type, at less than 1.5 USD per piece. In contrast, the repair cost of damaging the female threads by over-tightening the drain bolt with excessive torque to stop seepage far exceeds the cost of the gasket. Although seepage may not occur at all no matter how many times the gasket is used, there is a risk of damaging the threads by repeatedly tightening the gasket to a high torque without being aware of it, as the gasket loses its crushing response.
Coating-type gaskets are effective in preventing subtle oil seepage from the oil drain bolt, and are also effective in preventing extra work during engine oil changes, the most basic part of motorcycle maintenance. Whether you have been lucky enough to use the same bolt and have had no seepage or leakage, or whether you have been wiping off the oil with a rag every time you find oil that is seeping out slowly, we recommend that you use a new gasket that matches the size of the drain bolt on your motorcycle.
- Point 1: Gasket coated on metal material follows and seals even when the surface of the tightened part is uneven.
- Point 2: When using aftermarket drain bolts, purchase the size that matches the thread diameter of the drain bolt.
