I've noticed many, including myself, have had problems reinstalling the dipstick after changing the O-ring. Since I had the oil pan off, and everything was free and clear, I wanted to take some measurements and post a pic of the machined dipstick hole.
Refer to the pic below:
I measured about 28 mm across the top of the opening which immediately bevels down to a 24.2 mm diameter shaft that is 15 mm deep, ending at a narrow shelf or lip. The O-ring seats on this lip which is only 1.0 mm wide.
The O-ring slides down this is the section and mine had a rough surface texture; like a large diameter drill bit had hogged it out w/o finishing the surface. The O-ring is compressed while pushing through this part of the hole and it's easy to see that if the O-ring is even slightly too large in diameter, it could be difficult to overcome the friction on this rough surface.
The diameter of the hole below the lip was 22.3 mm wide. This the part of the hole where the taper of the dipstick tube slides into.
The dipstick tube:
The dipstick measured about 7.25" or 185 mm; and it had a slight taper to it, measuring 21.5 mm at the top, where the O-ring seats, and 20 mm at the base. The ridge at the top of the dipstick tube which prevents the O-ring from sliding further up, and which seats the O-ring to the lip, measured out at 23.7 mm.
The O-ring:
The diameter of the O-ring when on the tube is 25.4 mm (used), This dimension is not quite a millimeter larger than the shaft its sliding into. So you can see that the O-ring needs to be compressed in the shaft before it seats on the lip; and even the slightest increase in diameter may cause the O-ring to hang up on the rough cut sidewalls of the shaft.
Summary
Consequently, one may observe how the close tolerances often make this install problematic. First the tube needs to be almost perfectly aligned to the hole. Any misalignment, and the end of the dipstick tube gets caught on the lip.
On my 325xit, the driver's side motor mount bracket bolted to the engine block prevented the dipstick tube from being positioned in the vertical. Because I had the oil pan off, I could insert the dipstick tube into the pan before securing the pan to the block. Otherwise I would have had to remove various items above this location in order to insert the tube in the necessary perpendicular orientation.
Furthermore, the compressed O-ring can have a difficult time sliding over the rough surface near the top, so either be certain of your sizing or obtain a genuine BMW O-ring. Hope this helps somebody. gordo
Refer to the pic below:
I measured about 28 mm across the top of the opening which immediately bevels down to a 24.2 mm diameter shaft that is 15 mm deep, ending at a narrow shelf or lip. The O-ring seats on this lip which is only 1.0 mm wide.
The O-ring slides down this is the section and mine had a rough surface texture; like a large diameter drill bit had hogged it out w/o finishing the surface. The O-ring is compressed while pushing through this part of the hole and it's easy to see that if the O-ring is even slightly too large in diameter, it could be difficult to overcome the friction on this rough surface.
The diameter of the hole below the lip was 22.3 mm wide. This the part of the hole where the taper of the dipstick tube slides into.
The dipstick tube:
The dipstick measured about 7.25" or 185 mm; and it had a slight taper to it, measuring 21.5 mm at the top, where the O-ring seats, and 20 mm at the base. The ridge at the top of the dipstick tube which prevents the O-ring from sliding further up, and which seats the O-ring to the lip, measured out at 23.7 mm.
The O-ring:
The diameter of the O-ring when on the tube is 25.4 mm (used), This dimension is not quite a millimeter larger than the shaft its sliding into. So you can see that the O-ring needs to be compressed in the shaft before it seats on the lip; and even the slightest increase in diameter may cause the O-ring to hang up on the rough cut sidewalls of the shaft.
Summary
Consequently, one may observe how the close tolerances often make this install problematic. First the tube needs to be almost perfectly aligned to the hole. Any misalignment, and the end of the dipstick tube gets caught on the lip.
On my 325xit, the driver's side motor mount bracket bolted to the engine block prevented the dipstick tube from being positioned in the vertical. Because I had the oil pan off, I could insert the dipstick tube into the pan before securing the pan to the block. Otherwise I would have had to remove various items above this location in order to insert the tube in the necessary perpendicular orientation.
Furthermore, the compressed O-ring can have a difficult time sliding over the rough surface near the top, so either be certain of your sizing or obtain a genuine BMW O-ring. Hope this helps somebody. gordo
Dipstick install after O-ring replacement, some solutions
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