Fork seal stiction(2019)

cliffa said:
I guess the holders are machined to fit, nullifying the need to "adjust" the seals ?
Click to expand...
Yeah, Cosentino appears to have moved the seal _and_ the top bush from the slider into the collar. By lengthening the collar, the space occupied by the top bush collar and the seal is bridged.
Sliders may travel further if longer springs and damper rods are also fitted, but lateral loads now have to be transmitted across the threaded slider section, and I am not convinced this is a good idea.

Ariete Ari.003T seals are considered premium m/c fork seals. However, OD is 48mm and probably a bit more.

Ludwig and Marinatlas, I guess you sanded the OD to enable fitment in the 47.75mm counterbore. Due to the inherent wear resistance, I guess the synthetic rubber doesn't respond well to sanding?

- Knut
 
mdt-son said:
Yeah, Cosentino appears to have moved the seal _and_ the top bush from the slider into the collar. By lengthening the collar, the space occupied by the top bush collar and the seal is bridged.
Sliders may travel further if longer springs and damper rods are also fitted, but lateral loads now have to be transmitted across the threaded slider section, and I am not convinced this is a good idea.

Ariete Ari.003T seals are considered premium m/c fork seals. However, OD is 48mm and probably a bit more.

Ludwig and Marinatlas, I guess you sanded the OD to enable fitment in the 47.75mm counterbore. Due to the inherent wear resistance, I guess the synthetic rubber doesn't respond well to sanding?

- Knut
Click to expand...
I fitted them as well, but I don't remember if I sanded them or skimmed a bit off on the lathe.

I understand what you mean about the load on the threaded collar, but wonder how deep they protrude into the sliders? Maybe @coseng could comment?
 
cliffa said:
I understand what you mean about the load on the threaded collar, but wonder how deep they protrude into the sliders?
Click to expand...
No further than depth of the counterbore for sure, which is 7/8". It would be interesting to learn if any load transfer is possible in the non-threaded part by expansion of the collar as it abuts the counterbore floor.

- Knut
 
ludwig said:
Yes, it is a bit fiddly to reduce the OD.
For my N15 I made slider extensions (something like Cosentino) and use Ariete seals with 47 mm OD.
Click to expand...
Ariete seals are made of a special nitrile rubber formulation which can be glued using a Silicone rubber adhesive that resists oil and humidity very well.
Why not glue thin aluminium foil to the 47mm OD (ARI.051), taking the dimension up to the desired diameter of the counterbore? The seal doesn't need to be a very tight fit, as is kept in place by the collar.
ARI.051 is slightly thinner than the stock seal (11mm), so may need a thin steel washer above to ensure the seal is compressed by the collar.

Machining neoprene requires ingenuity.


Sanding at room temperature may work, but the material will gum up your paper pretty fast. Clamping the seal in a lathe or on a mandrel isn't easy, so I guess your best bet is to hold it with your fingers while sanding on a continuous band sander. This doesn't warrant a consistent diameter though.

- Knut
 
mdt-son said:
Ariete seals are made of a special nitrile rubber formulation which can be glued using a Silicone rubber adhesive that resists oil and humidity very well.
Why not glue thin aluminium foil to the 47mm OD (ARI.051), taking the dimension up to the desired diameter of the counterbore? The seal doesn't need to be a very tight fit, as is kept in place by the collar.
ARI.051 is slightly thinner than the stock seal (11mm), so may need a thin steel washer above to ensure the seal is compressed by the collar.

Machining neoprene requires ingenuity.


Sanding at room temperature may work, but the material will gum up your paper pretty fast. Clamping the seal in a lathe or on a mandrel isn't easy, so I guess your best bet is to hold it with your fingers while sanding on a continuous band sander. This doesn't warrant a consistent diameter though.

- Knut
Click to expand...

Hi, Yes that is how you do it, continuous belt sander. It is very straightforward. Hold the seal loosely on the ID with the forefinger of one hand and maintain 90° to sander with thumb & forefinger of the other hand. The seal rotates quite slowly opposite to belt direction, the result is highly accurate and more than adequately concentric to seal diameter.

Have a good whitsun weekend,

Martin
 
mdt-son said:
Yeah, Cosentino appears to have moved the seal _and_ the top bush from the slider into the collar.... but lateral loads now have to be transmitted across the threaded slider section, and I am not convinced this is a good idea.
Click to expand...
Don't know about Cosentino's, but my extension moves the top bush 25 mm up.
The length of the bush below the lip is 35 mm, so it extends about 10 mm into the slider .
The lateral load is thus taken up by the extension and the slider proper.
The fact that the 2 bushes are further apart gives them an easier life.
 
The increased distance is desirable and will give the upper bush an easier life for sure - that is, IF the supporting condition is rigid. The actual rigidity of the fork extension is my concern. A threaded slider extension will never be as rigid as the slider itself, and even a tiny angular misalignment (wiggle) by way of the threaded connection and inferior rigidity of the extension sleeve will kill the objective of giving the bush an easier life.

The sub-optimum solution would be a longer slider of course. The optimum solution in terms of stiffness is - and I hate to say this - the USD fork, where bush spacing can be 2-3 times that of a traditional design.

- Knut
 
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