Sanding forks

While looking for Ariete fork seals online, I ran into the following advise. I can't remember where I saw it, but someone said that before installing new tubes. you should sand them with 2000 grit sandpaper. The point was that the manufacturers only go so far to polish them and they can be a lot smoother, thereby helping fork seals to resist wear. Any roughness would be annular and the seals move longitudinally. I have just purchased new tubes from Mitch Klemph that came from Andover Norton.
I hit them with the 2000 grit and I feel that it made them smoother. Under magnification you can see annular marks (we are talking very small). They are hard to see until you begin sanding, and are reduced by additional sanding. I don't have them gone but reduced considerably. I don't know if I am imagining it but the tubes do feel smoother. I am considering hitting them with the polishing wheel and compound.

I think the argument could be made that they could be too smooth. That the roughness helps to hold lubricant like the crosshatch on a cylinder wall.

Any one have a thought on this?

I don't think they can be too smooth. Take a look at the rams on an excavator or similar piece of equipment. One of the reasons they cost a lot of money is because of the care taken in polishing the ram.

With that said, I'm not sure how to best attack the problem after it is chromed.

rvich said:

I don't think they can be too smooth. Take a look at the rams on an excavator or similar piece of equipment.

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Good point.

rvich said:

With that said, I'm not sure how to best attack the problem after it is chromed.

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What I am sanding (polishing) now is the chrome. I believe that these tubes are machined, hard chromed and then re-machined. It is the final polishing that I believe is not taken far enough.

POLISHING... yes, do it, in a lathe, be consistant. Diamond paper will cut the chrome.
And I agree, the surface finish on may parts is shameful. Why I chose Forking by Frank. Old school rules.

Years ago I bought some cerium oxide powder for polishing glass. The original project has no bearing here but the remnants of that powder have been used for a lot of other polishing projects. It might work well on chrome.

https://www.amazon.com/Cerium-Oxide-Glass-Polishing-Compound/dp/B009XUAA4Y

Russ

Crocus or Crocus Cloth. If you decide to use it on a lathe, exercise extreme care to avoid getting wound up in the work piece.

I am doing mine by hand in a longitudinal direction. Any remaining roughness would not be opposite the direction of seal travel.
I may be getting ridiculously nit picky here.

Hi
Worked in Hydraulics most of my life, highly polished surface finish is not what you need, the surface finish needs to be a certain roughness to retain oil for lubrication of the seals to slow them down from wearing out.

This a snippet from a paper on the subject.

"The surface roughness of hard-chrome plated piston rods progressively changes during the component’s life cycle. The surface typically becomes smoother over time, which prevents the surface from maintaining a thin film of lubricating oil. The result is higher friction against piston rod seals. Micro-cracks can also form, leading to abrasion of the chrome tips on the piston rod surface and the formation of longer score marks across the entire running surface. These changes have a negative impact on the entire tribological system and can lead to functional failure of the hydraulic equipment."

Unless you have a surface roughness tester and can use it, you are probably making things worse, one quoted finish Ra 0.05 to 0.30 μm.

Best regards
Burgs

Burgs said:

Hi
Worked in Hydraulics most of my life, highly polished surface finish is not what you need, the surface finish needs to be a certain roughness to retain oil for lubrication of the seals to slow them down from wearing out.

Unless you have a surface roughness tester and can use it, you are probably making things worse, one quoted finish Ra 0.05 to 0.30 μm.

Best regards
Burgs

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There you have it! Your original thought turns out to be correct. Another example of why you shouldn't listen to me!

Although I am guessing that the above mentioned surface doesn't have annular rings left from machining left in it.

Interesting set of observations. In my experience Norton replacement stanchions are miles ahead of their Triumph and BSA counterparts; yet they responded well to the part number seals; the stanchions (Triumph & BSA) look like junk, but work well enough with visible annular machining (?) yet the ones on my BSA Victor hasn't leaked, go figure.

RoadScholar said:

yet the ones on my BSA Victor hasn't leaked, ...

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Something is wrong, you need to investigate. Something needs to be fixed.

Dances with Shrapnel said:

Something is wrong, you need to investigate. Something needs to be fixed.

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No oil...!

Dances with Shrapnel said:

Something is wrong, you need to investigate. Something needs to be fixed.

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Fast Eddie said:

No oil...!

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Dances with Shrapnel said:

Something is wrong, you need to investigate. Something needs to be fixed.

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Fast Eddie said:

No oil...!

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You two are great at raining on a parade. Time for a spot of tea and a few prunes?

The Victor has a full compliment of fork oil and hasn't leaked, and, yes, I was a bit surprised. My point, and I must have made it a bit too subtlety, is that the seals appear to have a decent bandwidth of tolerance, and if they end up weeping a bit, then all the more English...

Burg,
Thanks

Xtinct
No problems, one of my GT750s has glass smooth chrome on the stanchions and is a pain in the but (oil leaks), need to follow my own advice and fit a new set or have them re-chromed.
I have Andover stanchions in my Combat and there are no leaks and the finish looks good.
Burgs

If you look at the surface finish of an Ohlin's male stanchion, the titanium nitride is like a golden mirror; no hash marks or any otherwise rough surface finish. I think the parameters for hydraulic cylinders may be a bit different than suspension components as the latter are in almost constant motion and undergo frequent reversals in direction. Seal stiction is one of the many small niggles suspension gurus try to mitigate so those reversals can happen with minimal delay and the dampers can do their job. Has anyone ever seen a factory fork tube on any motorcycle display anything but mirror-like chrome (or DLC, the latest whiz-bang anti-friction coating)? 45 years in construction has revealed many hydraulic rams starting out with hashes in the finish and getting polished to mirror quality in use. But I've never seen a motorcycle fork like that.

Hi Danno
It would be interesting to know what the surface finish is on the Ohlins as it very hard to measure with the eyes, yes even the finish Ra 0.05 to 0.30 μm looks polished to naked eye but definitely not highly polished, or mirror like when you look at them with a Loupe.
When hydraulic cylinder rods get polished from wear, usually from the rod bearings heat and bad oils, rod seal failure is on the way and simply replacing seals is a waste of time. to fix you need to re-chrome or fit new rods.

Hydraulic cylinders face some very harsh operating conditions, high speed, high frequencies, extreme mechanical shock loadings very high shock pressures as well, as stiction is also a problem in some instances believe it or not.
There has also been a hell of lot studies been done and a lot of papers written on the problems with hydraulic cylinders and rods, lots of different materials and finishes have also been trialed and tested over the years, ceramics, HVOF, lubrication, bearings materials etc.

In the end I still the shock absorber as a hydraulic cylinder in principle when it contains and share the same problems.

But there are far more educated people than me out on this subject.

Best regards
Burgs

In the end I still (consider) the shock absorber as a hydraulic cylinder in principle when it contains and share the same problems.-Burgs

The same thing only different. Sprung from recoil-absorbing cannons by way of the spyglass.

And all arcane bs aside, you can remove small nicks and imperfections, at least enough to prevent seal-cutting, with 1500-2000 wetordry, but I'm not sure if honing the surface to work lap the seal like a cylinder and a piston ring is a necessary practice. Or a good one.