TOPIC:

Edou wrote:

Unless damper oils are a factor 10 more dense than water I'm sort of at a loss here. ...

With what? The maths, or mentally separating the concepts of density & viscosity? I'm not sure I can help with either, I haven't (yet) come up with a paradigm that doesn't have immediate & obvious logical flaws

A lot of viscosity is down mostly to the size/shape of the molecules that make up the liquid - water for instance has two light & small hydrogen atoms & one (heavier) oxygen atom, sugars (like syrup) are strings or carbon, hydrogen & oxygen atoms, oils tend to be big hairy long chains fo the same ...


A quick thought experiment for you - boiling spaghetti. Imagine three identical pans of water, each with identical weights of pasta. Further assume that it's 500g of 500mm length, and a litre of water. Each pan and it's contents weight the same, and have the same density. In the first pan, imagine you've broken the spaghetti into 25mm-50mm pieces, the 2nd one, just snapped it in half. I the third, it's in the full length. Which is easier to stir?





If you think that's a bad example, the next best one would have involved me trying to convince you that a buckets full of Lego and another full of Stikklebricks were in fact liquids

I get the basic concepts, Jonny.
But the math just won't add up...

Jonny wrote:

A quick thought experiment for you - boiling spaghetti. Imagine three identical pans of water, each with identical weights of pasta. Further assume that it's 500g of 500mm length, and a litre of water. Each pan and it's contents weight the same, and have the same density. In the first pan, imagine you've broken the spaghetti into 25mm-50mm pieces, the 2nd one, just snapped it in half. I the third, it's in the full length. Which is easier to stir?

thats genius, no way to explain it better

Seems to be indeed a (weird) coincidence that TRF brand their oil "VG" - it's not related to the ISO norm.

Non-existant user wrote:

VG is also on the latest TRF charger, tire warmer, power supply and motor checker.

Now that I'm not following Tamiya logic things make sense again. And the math adds up.
The ISO VG 32 jack oil I was using is simply #32 (or so) in Tam silicon oil terms. So very thin, which kinda matches.
The approach in the first post wasn't very scientific to begin with (even though it should mostly lead to the same conclusion).
I think a difference in the temperature criterion is the culprit there...

Edit -

The ISO VG 32 jack oil I was using is simply #32 (or so) in Tam silicon oil terms. So very thin, which kinda matches.

At 40 degrees celcius, that is (not showing the worms again).

So if Tamiya measures at room temperature, you just gotta recalibrate this graph to metric and extrapolate.


Source : www.engineering..._1206.html

I'll put a lid on it now.

Taking the lid off...

I reckon one can multiply the ISO viscosity by about 1.65 to go from the 40 degrees data to room temperature.
But that's not the main purpose of this post.

One big reason to not use hydraulic jack oil for CVAs - reactiveness with plastic.
Shocks that I hadn't used for a while had black sludge at the bottom and I had a hard time to make them work smoothly again.

Edou wrote:

... black sludge at the bottom and I had a hard time to make them work smoothly again.

Black o-rings swelling & breaking up?


Come to think of it, I've had inexplicable sludge in used Tamiya cars/shocks I've bought ... despite the shocks being full & having no evidence of leaks, there's often crud suspended in there, ranging from black granules a tiny bit smaller than sand grains, to really fine stuff that leaves a dark brown trail through the oil.

TBH I've never thought too hard about it, just cleaned the shocks out & replaced the seals & oil, mentally filing it under the same category as "Pixie poo" (this is the stuff that, despite having scrupulously cleaned and sealed motorbike fuel tank, filters, tap, fuel line, carburettor etc & filtered the fuel going into the tank, gets under the float chamber valves in the carb, causing petrol to whizz out of the overflows all over the road when you test ride a rebuilt bike )



Alternative explanation - see around the 21:00 minute mark in "Cast A Deadly Spell"

O-rings were red and some of the sludge seeped into the upper one...
My bet on being most responsive to jack oil would be the piston in this case.
It was really dark black stuff, mostly "separated" from the damper oil itself.

I wrote:

hard time to make them work smoothly again.

Don't think it helped I tightened the adjuster rings too much.