I want to change the oil in a shock to increase damping. I have no idea what oil is currently in there. I've guessed in the past, and it's worked, but I'd like to be a little more accurate this time. Any ideas on measuring the viscosity of what's in there now?
if you're just trying to compare what you have now vs. what's on your bench, you could count the drips over a certain time through a small opening - vary the opening size (maybe a drilled hole in the bottom of a cup or something) so the result is meaningful, then compare the two. Might have two measurements the same for different viscosity liquids, then you'll have to measure over a longer time.
To compare against a known standard - like 30W, is harder.
I dunno, seems to me you could lay your hands on a 30W reference sample fairly easily.
Spread test? If you can get a small repeatable sample of a known weight and your mystery fluid, and drip that sample onto a solid surface - glass or plastic or the like, and allow it to spread over a certain timespan. The larger the circle the more viscous? Kinda like the "slump test" to determine the solidity of mixed concrete? Thats a total stab in the dark though-no idea if this test is meant to work on oils. Good luck.
I once saw a viscosity scale. It came with a house paint sprayer that my Dad had. It was a plastic stick with a narrow V cut into it. Maybe 2" long with a 3/4" opening. You dipped it into the paint and then it had a scale on it depending on where the paint closed up the "V".
To compare different fluids on hand this should make it fairly simple. Not sure where you would come up with a calibrated stick?? Paint store??
It wouldn't be that hard to make a poor-man's viscometer with a narrow, tall graduated cylinder and a ball bearing.
4cylndrfury wrote: Spread test? If you can get a small repeatable sample of a known weight and your mystery fluid, and drip that sample onto a solid surface - glass or plastic or the like, and allow it to spread over a certain timespan. The larger the circle the more viscous? Kinda like the "slump test" to determine the solidity of mixed concrete? Thats a total stab in the dark though-no idea if this test is meant to work on oils. Good luck.
This. Viscosity is even measured in square meters per second or something like that, isn't it?
However, the larger the circle, the LESS viscous is it.
Taste?
An automotive paint supply store may have a paint viscosity cup (like slantvaliant linked to). Ask them how to use it properly--it's not that difficult.
I have the equipment to measure viscosity in centipoise. Probably a bit far to ship an ounce of something though.
Oil SAE 10 65 centipoise (cps)
Oil SAE 20 125 centipoise (cps)
Oil SAE 30 200 centipoise (cps)
Oil SAE 40 319 centipoise (cps)
Oil SAE 50 540 centipoise (cps)
Oil SAE 60 1,000 centipoise (cps)
Oil SAE 70 1,600 centipoise (cps)
Thanks for the ideas.
The taste idea is tempting, but I think I'll look into the cup idea. If I can't find something suitable for light oils, then I'll make it. I have every available viscosity in suspension fluid from 2.5W to 30W, so I can do some good comparison. I'll post the results.
That article in Classic Motorsports on the Koni shock rebuild made it sound like shocks took a real light viscosity oil in the 5 range.
How would you like to change your damping characteristics and why do you think the oil will yield the result you are looking for?
The shocks are underdamped already, and I'm increasing the spring rate, so even more is required. The damping can be altered by changing the viscosity of the fluid.
Keith wrote: I dunno, seems to me you could lay your hands on a 30W reference sample fairly easily.
But then one needs to know: Is suspension fluid measured on the same viscosity scale as motor oil?
I know that transmission and diff fluid are measured on a different scale, so why wouldn't suspension fluid be measured on it's own scale?
Use motorcycle fork oil or shock oil. you'll need to know how much can out and if its under presure and single or twin tube design. There are some neat under cover ways of doing it. I've don'e a strut behind the two bolts that held the spindel before in a stock only class for a freind. Once the spindel was attached tech could not see the screw and washer. never could figure out how to presureize that unit to keep it from foaming and cooler.
That's what I'm doing. I've done a few sets in the past, and they've worked well, even long term. I just want to get a better handle on what's coming out, what's going in, and what the results are.
You sir need a shock dyno!
See next post
Any ideas on how to build a shock dyno? 
http://www.circletrack.com/howto/82884_buildling_shock_dyno/index.html
there are better plans out there that use air cylinders but google found this quick.
http://www.shocksetup.com/pdfs/ReadMore_RebuildManual.pdf
Item on ebay, for $10 you can get a cup on E-bay or just drill a 4mm hole in the bottom of some container. "4.0mm orifice, similar to Ford #4, DIN #4 and Sears cups "
http://cgi.ebay.com/4-0mm-paint-viscosity-cup-viscosimeter-measurement-4-/300266891078?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item45e94d2746
Thanks for the ideas.
Like usual, I was making it more complicated than it needed to be.
A trip to Dollarama, and a Mikuni main jet, and I'm in business.
MINT
Now that using your noddle!
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