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Boffins please help with this one

What exactly are you asking, Graham? The density of 15W fork oil compared to mercury?
 
Graham, go to the oil company's website and get the typical Specific Gravity (SG) then compare it to the SG for Hg from the Periodic Table. BTW ATF is a better oil to use the fork oil but really it's the relativity between each column of the manometer that's important not the actual reading which will vary according to atmospheric pressure, humidity and altitude et al.

Peter
 
My first thought ... wow I know as much as Pete on this one ... pity its NO and that Pete knows so much about everything else I know nothing about...(honest praise/no pipi$$take)

this is an intriguing question and is bound to be a great read

BTW - Thanks Graham for the great tips on the GIVI pannier thread I started .. Art
 
Holy moly Graham, now you're askin..... I'll dig out the physics texts tonight.

I am also curious as to the reason behind the enquiry.

Rene's query is relevant - I am assuming you want to know what the column height would be for 15w fork oil if you have a vaccum that will produce a 1cm column of mercury with that same vaccum?

Big ask to calculate but could of course be done -might be beyond my meagre brain resources though, we shall see.
 
Gosh! And I felt sure that I was the only one of this august group who had forgotten all the physics ever learned!

I guess it is the relative specific-gravity of Hg and 15W fork oil which is the issue. Why I want to know is that my oil-filled manometer seems so wonderfully sensitive compared to the Hg one I used to use that I'm interested to know how accurately I need to get the balance reading. At 3,000rpm I must be getting within 1mm or so, and at idle maybe within 3mm, but that is slightly affected by the stepper-motor chiming in as it sees fit.

Yesterday I set the tappets - left inlet had opened to 0.15mm and all others had not moved in 10,000km - fitted new outer plugs - the gaps had opened somewhat - reset the TPS and balanced the vacuum, and then went for a good ride. The throttling on this bike is really extremely good compared to when it was new - and to a Buell. As some may recall the vacuum reading on my bike was 2.5cm Hg out of balance and no one here had an Axone or even knew that the TPS had to be reset electronically. Times have definitely changed for the better. It was here that I met Kiwi Dave who first made me aware of that but it still took the dealer a long time to accept it and buy an Axone.

For a while now I've been thinking of quitting the Breva for something much lighter in recognition of my increasing decrepitude, but every time I take if for a ride it reminds me of what a lovely bike it is, even if just to look at sitting in the garage, and that I don't think I could part with it. What I have decided to do now is be extremely careful when coming to a stop and putting a foot down, and not to carry a pillion anymore.

Anyway, back to the thread - at a guess 1cm Hg must be equal to at least double that of 15W oil judging by the effect that even the slightest movement of the adjusting screws has. Just would like to know by how much. Inquiring mind I guess, which is a good sign as age accumulates.
 
I too, pondered on this question, then thought, sod it, got my oil damped Davida vacuum guages out and balnced the throttle bodies without ever feeling guilty that I didn`t know (or give a f***) the answer :woohoo: :woohoo: :woohoo: When questions like that arise, I whimp out, take a sideways step and find an alternative question for the same outcome. Does that make any sense? or am I lost in a wolrd of my own?
 
Brevabrabo
There is a very comfortable chair in my garage already, and sometimes I do just sit there and admire things. No nurse in attendance but a very loving wife. Could be a lot worse!

commando tod
Hopefully you also used VDSTS to reset the TPS in conjunction with your vacuum balancing?

Question: Given equal vacuum acting upon them, if Hg rises 1cm, how much will 15W oil rise? Sounds a simple enough question, but I'm beggared if I can remember how to work out the answer. Then again I've forgotten how to solve a quadratic equation too so I'm clearly past it. Can use VDSTS though.
 
Just pulling a few numbers out of my head here. Standard atmospheric pressure is about 760 mm of Hg, or about 30 inches. I believe that is also equivalent to something like 33 feet of water column head pressure. Oil is slightly less dense than water, sooooooo... my best guess is that your oil manometer will be something like 12-15 times more sensitive than mercury.

Hope this helps,

Howard
 
Thanks, Howard. Excellent.

Well I'd have guessed at about x5. Anyway the sensitivity is a great thing although a shaking hand is a problem! Best to be sober and not too excited when on the job.
 
Been away for the weekend so only just seen this thread.
I would say that 1 to 3 mm of oil difference would certainly not be readable in mercury.

And the U tube manometer,filled with water or oil (I use transmission fuid cos it's red) is many times more accurate than any vacuum guage, especially when you are trying to compare two guages.
Have they been calibrated? If not, you might be getting no-where.
The U tube needs no calibration, and can never give a false reading.

Graham, if you are measuring the difference in mm then you have no problems with the balance.
 
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