Sizing an oil seal? | MIG Welding Forum

I realise, after no less than 50 years taking bikes and complete engines apart and (after the first couple of years....) successfully putting them back together again, I've only ever bought oil seals as either a manufacturer's part or by the markings.

Now, as part of my fascination with stone age machinery, I have an old Chinese sidevalve 750 flat twin sidecar outfit, a Chang Jiang CJ750. It runs actually very nicely despite being even more primitive than my Harley. It needs immediately some fork seals, and I found a couple in its huge tool kit. Sadly they are old and hard with rusted springs, and have a numerical code which seems to relate only to a part number.

What I know is that the fork tubes are 40mm, and the overall size of both seals is 47.5mm. Internally they are 38mm- 2mm under the size of the tubes. So my questions are , is this normal, or do I buy new seals based on the shaft size? I can order the real thing from China, but it will take time and seals from say Timken are likely to be better quality. And no doubt there will be seals in the dripping final drive, the weeping gearbox etc etc.......

I'm very fond of it already. I usually greet it in the voice of a Bond villain, 'Ah so, Mr Chang will see you to your doom Mr Bond.....'. Since it is a motorcycle application, you might do well to look for them at a motorcycle fork seal specialist rather than a general bearing and seal supplier.

The first one that pops up on a search for me is:

https://www.brooksuspension.co.uk/fork-seals/

I am sure if you tell them the tube outer diameter, the internal diameter in the fork lower and the thickness, they will have something for you.

Being of Chinese origin, it is vanishingly unlikely they will be to imperial dimensions.

Author: Subject: Measuring Oil Seals? JeffHs

posted on 28/1/12 at 07:47 PM Measuring Oil Seals?

I want to see if I can source standard seals from on-line bearing suppliers to replace Ford ones. Catalogue OD and thickness are self-evident but what does the ID of the seal refer to - is it shaft size, seal dimension unfitted, shaft size plus a tolerance?
I keep being amazed how little I know! But someone on here will.
i cant remember now, but i read it recently on one of the online bearing shops, they had a full description of what the codes mean. Was one of the first links on google, sadly i didnt save it.





RAYLEE29
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posted on 28/1/12 at 09:11 PM Hi, the sizes are housing size shaft size and width also there are variants like double lip seals an ones where the seal lip is inset also type of material. most seals will have the sizes on them eg 37 47 6.
hope this helps
Ray




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Why not just get the Ford ones? Or are they silly expensive?
I've used these a few times and they've always been very good.

http://simplybearings.co.uk/shop/index.html

This is what they say about the seal dimensions.


What bore diameter should my oil seal have?

The required inside diameter of an oil seal is the same as the shaft size it will be running on. (the seal manufacturers make allowance for the seal to be a snug fit on a shaft)

If you can supply us the bore, diameter and width you require we can locate the seal for you and send you a link to it.
Chippy
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posted on 28/1/12 at 11:07 PM +1 for Simply Bearings HTHRay




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