How do you size oil seals?

08 Apr.,2024

 


https://thecabe.com/forum/threads/c...-3-gang-german-bottom-bracket-3-speed.106395/

Thanks for the suggestions! I am finding things that are closer to what I need online thanks to your help. There is a Motion Industries near where I am staying, but I'm working hours that would be illegal in the EU so won't be able to bring the brittle pieces inn while they are open. Taking pictures of small black objects is a little challenging for me. One seal has a lip around the outside like a small brake wheel cylinder seal, the other is flat with a lip on one side of the ID and a recess on the other. The third is a ring of metal channel filled with Buna rubber. This last one I think can be repacked with string packing fairly easily. I am basically in a motel room, and I don't trust my Harbor Freight digital calipers, which seem to consistently read .1mm too small. Most of the measurements I take seem like an odd size. Since this is a bicycle some but not all of the parts are Imperial bicycle standard, and some others are Metric. If anyone is interested, I have a thread on the bike on a bicycle nerd board at:

Identifying oil seals can be tricky especially the imperial sizes so here is a little guide that will help you get your job up & running again quickly

Metric Oil Seals


Metric oil seals are more or less straight forward as the size is stamped on the seal for example 20 47 7 this indicates that the inside is 20mm, outside 47mm & width 7mm, some oil seals have different lip arrangements 


SC=R21 & TC=R23 being the most common R21=Single Lip R23=Double Lip


So for example if you had on your oil seal TC 20 47 7 you would now know that you would need a double lip seal with a 20mm inside, 47mm outside & 7mm width.


Imperial Oil Seals


imperial oil seals are a little more tricky as the numbers on the oil seal are not in fractions & they always start with the outside diameter first for example 300 212 37 this indicates that the oil seals sizes are 2.1/8" inside, 3" outside & 3/8 wide, below is a table to help you convert these numbers,


1/16           0.06
1/8             0.12
3/16           0.18
1/4             0.25
5/16           0.31
3/8             0.37
7/16           0.43
1/2             0.50
9/16           0.56
5/8             0.62
11/16         0.68
3/4             0.75
13/16         0.81
7/8             0.87
15/16         0.93
1                1.00


To help you understand how the table works with imperial oil seal numbers here are a few example references,


(remember the first number is always the outside diameter)


137 62 25 = 5/8" inside x 1.3/8" outside x 1/4" wide


187 125 25 = 1.1/4" inside x 1.7/8" outside x 1/4" wide


150 250 37 = 1.1/2" x inside 2.1/2" x outside 3/8" wide


To identify the seals lip arrangement see previous table above,


 


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