Hello, RPV.
This time I am trying to repair a tank cap fuel leak on an old Yamaha 2-stroke off-road vehicle. I did this a while ago and was able to fix the fuel leak without it recurring, so I wrote this article about it. I think it is a common part with other models of vehicles, so I hope it will be helpful for those who have one.
It is hard to tell from the picture, but there are traces of gasoline seepage from the tank cap key cylinder area. When driving after filling up the tank, there is a noticeable seepage and gasoline smell for a while. I thought about replacing the cap itself, but it would require an additional key dedicated to the tank, and it would be depressing to wonder which is the main key when riding, so I decided to identify the cause of the leak in this cap and repair it with minimal parts replacement utilizing this cap and key cylinder.
First, let's take a look at the tank cap through an X-ray. The O-ring can be seen in the blue circle. It seems that the O-ring is just a seal between the tank chamber and the outside air.
The O-ring only part is not supplied by the manufacturer and the price is a little over 5,000 yen for the cap assembly. I will try to replace the O-ring only.
First, the key cylinder (the metal part where the key enters) must be removed from the plastic cap. From the exterior, it is not clear how to remove the key cylinder.
Then, looking at the X-ray image further, we can confirm that there is a claw-like object that connects the plastic cap to the key cylinder in the red circle in the above image. To separate these two parts, move the key unit downward in the X-ray image (upward from the car body) while holding the claws toward the center using a thin screwdriver or the like. The image below shows the metal part protruding from the upper side of the key unit, which has already been separated. This metal claw holds the plastic cap and key cylinder in place.
Disassemble the tank cap and remove the O-ring.
Comparison of old and new O-rings. The left is the new ring and the right is the old ring.
Of course, get a fuel-resistant type. I measured the dimensions of the part where the O-ring fits and the deformed O-ring, and purchased the size I thought would fit.
The following are the product names and features of tank cap O-rings that seem to match my bike.
Inside diameter: 12.3
Outer diameter: 16.1
Thickness: 1.9
Material: 4D
I chose this one because the main ability required is that it is athletic compatible and gasoline resistant. o-ring size, etc. may vary depending on the model and year of the bike, so this is just a reference.
The car was assembled back together and is now complete. When I turn the key on the fuel tank, the rattle that I had before is gone, and the feel of a new car seems to have returned.
It has been over 6 months and the fuel seepage is no longer as bad as before.
