How to measure oil seals

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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Now let's talk a little about seal types. It was pretty easy to find well illustrated info on that. There are as many as 5 different types used on the 650 engine. Some types changed when seals were updated so you may not find all 5 on your particular machine. Most of the seals are the "SD" type, with a sprinkling of "SO" and "SDD" types thrown in. Here's cross sectional drawings of the various types .....



And here's a little tidbit of info about the "SD" type I found interesting, highlighted below .....



Looks like I'll be packing some grease into them before install from now on. Maybe it will help them seal better, and I certainly don't see it hurting anything.

There's been some oil seal talk recently, particularly about the cam shaft seals, and I realized I really didn't know too much about oil seals in general. So I decided to educate myself, which proved quite easy. One simple Google search turned up all the relevant info. Oil seals have a code number, usually stamped right on them, that gives the seal type and size. The 1st entry in the code is the seal type and consists of 1 to 3 letters. The numbers following are the size, in our case in MM (I.D. x O.D. x thickness). Determining the 650 seal types and sizes proved pretty easy because they are listed in the earlier factory parts manuals, so I made up a chart .....Now let's talk a little about seal types. It was pretty easy to find well illustrated info on that. There are as many as 5 different types used on the 650 engine. Some types changed when seals were updated so you may not find all 5 on your particular machine. Most of the seals are the "SD" type, with a sprinkling of "SO" and "SDD" types thrown in. Here's cross sectional drawings of the various types .....And here's a little tidbit of info about the "SD" type I found interesting, highlighted below .....Looks like I'll be packing some grease into them before install from now on. Maybe it will help them seal better, and I certainly don't see it hurting anything.