Ever wonder about fork oil?

[warewolf]

Originally Posted by meat popsicle

I am not prepared to swap the seals out. I just have the heavier springs, subtanks, and oil.

It's actually quite simple and easy. From the point you get to in order to drain the oil - the last step is to remove the compression valve from the bottom of the forks and remove the cartridge - basically all you have to do is remove the circlip that locks the oil seal in and pull the two halves apart by hand. Installation requires some form of driver to press in the bushes and seals, then the process is to continue as per an oil change. A bit of PVC drain pipe works as a driver, in fact I used a portion of an empty plastic bottle; it was a bit too flexible but got there nice & gentle like.

Oh, and the other modified tool is the 22mm spanner; it was too fat to sit in the cartridge top properly, so I took to it with a flat file to slim it down till it fits well. No more poorly-fitting spanner being ejected by the fork spring!

The WP expert here recommends NOK (WP OEM) oil seals, part BR6812E, yes these are the black ones referenced in other threads. He reckons the OEM dust wipers are a bit "factory mechanic," meaning too light-duty and designed for regular tear-down and replacement, not up to the rigours of NZ conditions and clubman use. So he recommends not the WP OEM NOK dust wiper (part BR6813E) but rather that specified by KYB, NOK part BR6653E. These latter are quite a bit tighter so protect the oil seals better (likely at the expense of stiction, TANSTAAFL). All these part numbers are for 48mm forks.

Go on, you know you want to!

[jgas]

Now a cheap assed redneck is gonna really screw up this discussion. I use synthetic transmission fluid in forks. I don't know how to compare viscosity or flow properties, but when I dip my fingers in fork oil and tranny fluid and do the ol' thumb-index finger feel test, they feel similar. When I pour them into the forks, they appear to flow about the same. I've been using it in my KTM WPs for 2 years. I do a tear down and seal change about every 6 months, and I ride A LOT. My bushings and seals are usually fine, sometimes I don't even need seals. My forks seem to leak less, and the action feels slightly smoother than with 5 or 7 weight fork oil. (I've used Silkolene, Maxima, Bel-Ray, and Spectro for comparison).

The only 2 arguments I've heard against tranny fluid is that it foams up and it might not handle heat. From what a buddy of mine that owns a transmission shop says, synthetic trans fluid doens't foam. And an automatic tranny in stop and go traffic in summer gets much hotter than your forks will ever get.

I know a bunch of riders and racers who use this stuff. If anyone can give me a reason to stop, I'll listen. My mechanic buddy trained by MMI with mucho experience say's I'm crazy. But I already knew that.

[meat popsicle]

Originally Posted by jgas

Now a cheap assed redneck is gonna really screw up this discussion. I use synthetic transmission fluid in forks.

aka ATF or the Bureau of Alcohol, Tobacco, and Firearms - so you have a vice? BTW, how much does the ATF cost you for a fork refill? My Redline LightWeight cost me $20... and once per year or even once every 6 months makes $20 pretty damn cheap.

Originally Posted by jgas

I don't know how to compare viscosity or flow properties, but when I dip my fingers in fork oil and tranny fluid and do the ol' thumb-index finger feel test, they feel similar. When I pour them into the forks, they appear to flow about the same.

Maybe you were not really asking, but viscosity is tested with a "viscometer", as I recall it is 2mm glass tubing, and the rate of flow through the tube is measured. The thicker the fluid the slower it flows right? Hydraulic fluids such as fork oil are further tested at several temperatures because users do not want the viscosity to change with temperature. Why? Because the fork action will change as they heat up and cool down and it is nice to know exactly how your forks are going to respond to those rocks you are about to charge over...

ATF is not tested as a hydraulic fluid because it is a lubrication oil. So I don't know if it has a high Viscosity Index or not. One site I read said the fork oil should have a VI of at least 150 to be reliable across the range of temperatures that forks will encounter. (BTW, A shock will need a MUCH higher VI because shocks heat up much more than forks.) I guess in your experience your ATF viscosity has been stable across the temperature range that your forks encounter. That could be because ATF has a high VI by accident (lucky you) or because you do not ride hard enough to experience these issues. Now don't take that as a personal insult - I don't know how you ride (except for ALOT) - this is just a discussion.

Originally Posted by jgas

I've been using it in my KTM WPs for 2 years. I do a tear down and seal change about every 6 months, and I ride A LOT. My bushings and seals are usually fine, sometimes I don't even need seals. My forks seem to leak less, and the action feels slightly smoother than with 5 or 7 weight fork oil. (I've used Silkolene, Maxima, Bel-Ray, and Spectro for comparison).

6 months is about half the recommended interval for USD WP 48s on a 640a, but you ride ALOT, so you may or may not be pushing the envelope in regards to fluid breakdown. That might be important or it might not; I just am trying to discuss this with you because ATF is brought up ALOT but not rigorously.

Originally Posted by jgas

The only 2 arguments I've heard against tranny fluid is that it foams up and it might not handle heat. From what a buddy of mine that owns a transmission shop says, synthetic trans fluid doens't foam. And an automatic tranny in stop and go traffic in summer gets much hotter than your forks will ever get.

Its not the max temperature that is important, it is the stability of viscosity across the range of temps that a fork goes through that is important to predictable fork action. One other thing I should mention that I know about ATF is the one SAE weight I have seen posted on ATF (Mobil 1) was 7.5wt, which is higher than the recommended SAE weight for my forks. Is it wrong? Not necessarily, but the forks will not work as designed by the WP tuners who specify 5wt.

Originally Posted by jgas

I know a bunch of riders and racers who use this stuff. If anyone can give me a reason to stop, I'll listen. My mechanic buddy trained by MMI with mucho experience say's I'm crazy. But I already knew that.

I can't give you a reason to stop, but the point of this thread is not to condemn ATF-users as heretics. My point was to give folks who are trying to find reliable indicators of fork oil performance the information they need to reliably tune their suspension.

[Luke]

So I changed my fork oil the other day, and the stuff that came out was grey muck. This was after about 9 months/10k miles after putting fresh fluid in. I'm going to start changing it every 3 oil changes.

Anyway, I took a longer look at Peter Verdone's site, and tried to figure out mixing. I want to change oil often, so Mobil 1 ATF sounds great. Problem is, it's too thick.

So the formula he uses to get the viscosity of the mixed oil is this:

%A,%B = percentage of oil A and B
VA,VB = viscosity of oil A and B (in cST)
VM = viscosity of the mix.

VM =( VA*%A+VB*%B)/100

reversing the formula, %A = 100*(VM-VB)/(VA-VB), %B = 100-%A.

Starte with Mobil1 ATF and cutting it with either RedLine Clear (superthin) or Silkolene Pro RSF 15. I figure, aside from the Mobil1, use good suspension fluid.

So figure out what sort of viscosity you want. I want to match Silkolene Pro RSF 5, because that's what's in the forks already, and it works.The viscosity of 26.7cST (from Peter's site)

Mobil1 has a viscosity of 34, and RedLine Clear is 5.5

So from the formulas above, I need to mix about 75% Mobil1 and 25% RedLine.


If you don't like math, here's a table:

	Cheap fork oil mix chart
	Red Line Clear		Mobil1		Silkolene Pro RSF 15wt
cSt @ 40C	5.5		34		92.95
10	84	%	16	%
12	77	%	23	%
14	70	%	30	%
16	63	%	37	%
18	56	%	44	%
20	49	%	51	%
22	42	%	58	%
24	35	%	65	%
26	28	%	72	%
28	21	%	79	%
30	14	%	86	%
32	7	%	93	%
34	0	%	100	%	0	%
36			97	%	3	%
38			93	%	7	%
40			90	%	10	%
42			86	%	14	%
44			83	%	17	%
46			80	%	20	%
48			76	%	24	%
50			73	%	27	%
52			69	%	31	%
54			66	%	34	%
56			63	%	37	%
58			59	%	41	%
60			56	%	44	%

I'm not cheap enough to use Mobil1 in my shocks, so I haven't done the numbers for viscosity at 100C, but someone motivated enough could figure that out, as well as the VI for the new mix by comparing the V@40C and V@100C values.

[bmwktmbill]

Originally Posted by warewolf

The WP expert here recommends NOK (WP OEM) oil seals, part BR6812E, yes these are the black ones referenced in other threads. He reckons the OEM dust wipers are a bit "factory mechanic," meaning too light-duty and designed for regular tear-down and replacement, not up to the rigours of NZ conditions and clubman use. So he recommends not the WP OEM NOK dust wiper (part BR6813E) but rather that specified by KYB, NOK part BR6653E. These latter are quite a bit tighter so protect the oil seals better (likely at the expense of stiction, TANSTAAFL). All these part numbers are for 48mm forks.

Go on, you know you want to!

Hi Colin,
Nice write up.
One trick I am using to save the OEM seals is to fill the internl recess between the dust seal and the main seal with grease and use a short external neoprene boot. This was recommended by Creeper.
The grease leaves a thin film that helps keep mud and the like from drying on hard. It may also seal out dirt and debris, I won't know until I change oil in the spring.
I did a long tour on rough roads last summer with no failures(15K miles).
At least half the tour was dirt, gravel or desert tracks.
bill.

[Luke]

Alright, so insomnia's getting the best of me.

I can't figure VI numbers, but I figured the viscosity at 100C for some of the mixes I posted above. The fancy oil / Mobil1 mix is better at high temps than cheap oil (bel-ray, etc), very close to Amsoil, and a little worse than fancy oil (redline, silkoline pro, etc). No big surprise, as Mobil1 is almost identical in viscosity and VI to Amsoil 10wt.

[jgas]

I'm self-admittedlly not a technical guy when it comes to bikes. I tend more towards trying something that I think might work, especially if it saves me a few bucks. I also live 60 miles from any bike shop, out in the sticks. When working on bikes on a Saturday, and needing parts or fluids, I tend to improvise rather than trek to a shop and back. It's led to some interesting fixes!. I actually tried the ATF trick at a MX track with a KDX, (yep, I was doing MX on a KDX, it was all I had). I blew a fork seal, and the fluid was pouring out. I was entered in two classes, with about 20 minutes between motos. I just pulled the fork cap and poured some in between motos, just guessed at the right level. Seemed to work ok. I wasn't fast at MX anyway. My results were no worse than usual.

I also read that Mobil 1 Synthetic ATF was 7.5 weight, and my WP forks needed 5 wt, but in past experience I could never feel much difference between 2 lbs of fork oil change. 5 lbs I could feel.

Anyway, my seat of pants feel while riding was that the supposedly heavier ATF felt lighter than the supposedly lighter fork oil. The fork action felt a little quicker and more reactive on both compression and rebound, which was backwards from what I expected. I was riding in extremely rocky and rooty terrain, very technical. Mostly 1st-3rd gear stuff, and a challenge to carry much real speed. The ATF felt like it worked better in that kind of terrain. It did blow through the stroke a little quicker, which was not a problem where I was riding.

As I said, I kept the ATF in 6 months at a time for 2 years with no problems. I'm convinced it is equal to or better than fork oil for me. And much cheaper.

Keep on coming with the technical advice, cause I sure need it! I might not be smart enuf to use it, but I like trying to read and understand it anyway. I truly admire the folks who can tune and tweak a bike and actually understand why what they are doing works or doesn't. The technical reaons are mostly Voodoo to me, especially suspension tuning. I just trial and error until I'm satisfied with a result.

[meat popsicle]

Originally Posted by Luke

Alright, so insomnia's getting the best of me.

I can't figure VI numbers, but I figured the viscosity at 100C for some of the mixes I posted above. The fancy oil / Mobil1 mix is better at high temps than cheap oil (bel-ray, etc), very close to Amsoil, and a little worse than fancy oil (redline, silkoline pro, etc). No big surprise, as Mobil1 is almost identical in viscosity and VI to Amsoil 10wt.

Hey Luke,

Are you looking for info on the ASTM method?

http://www.tpub.com/content/engine/1...s/14105_37.htm

"The V.I. of an oil may be determined if its viscosity at any two temperatures is known. Tables, based on a large number of tests, are issued by the American Society for Testing and Materials (ASTM). These tables permit calculation of the V.I. from known viscosities."

Here is the VI lookup table:
http://www.astm.org/BOOKSTORE/PUBS/1059.htm
$83 - doh!

So I looked up Mobil1 ATF, which goes for about $10/quart or half the price of Redline LightWeight. I don't get the attraction - $10 every 10K?

Not very helpful I know, but while I am posting I'll share a thread from ThumperTalk on fork oils: http://www.thumpertalk.com/forum/sho...d.php?t=578362

Originally Posted by jgas

...
Keep on coming with the technical advice, cause I sure need it! I might not be smart enuf to use it, but I like trying to read and understand it anyway. I truly admire the folks who can tune and tweak a bike and actually understand why what they are doing works or doesn't. The technical reaons are mostly Voodoo to me, especially suspension tuning. I just trial and error until I'm satisfied with a result.

I admire those folks too

Originally Posted by bmwktmbill

...
One trick I am using to save the OEM seals is to fill the internl recess between the dust seal and the main seal with grease and use a short external neoprene boot. This was recommended by Creeper.
The grease leaves a thin film that helps keep mud and the like from drying on hard. It may also seal out dirt and debris, I won't know until I change oil in the spring.
I did a long tour on rough roads last summer with no failures(15K miles).
At least half the tour was dirt, gravel or desert tracks.
bill.

FYI, on KTMTalk they discuss an oiled "sponge" trick instead of straight light grease. I think they use old air filters and cut them into donuts that fit inside the dust seal and oil them. Never noticed it posted here so I thought someone might be interested.

[warewolf]

Originally Posted by bmwktmbill

Nice write up.
One trick I am using to save the OEM seals is to fill the internl recess between the dust seal and the main seal with grease and use a short external neoprene boot. This was recommended by Creeper.
The grease leaves a thin film that helps keep mud and the like from drying on hard.

Ta. Sounds like an extension of the process in the WP docs which say to grease up various bits as it goes together. I second the short neoprene, they'll act as a secondary wiper but still allow easy access for maintenance.

btw the suspension guys here suggest a spray/wipe with silicon or oil or whatever on the stanchions regularly, particularly after a wash. I use Motorex Joker 440 (spray synthetic oil I think) per KTM's recommendation. Silicon spray is recommended by WP but KTM say use anything but! In other applications I find silicon sprays generate a salty deposit over time presumably as a result of corrosion, so I am very judicious with its use now.

Originally Posted by meat popsicle

FYI, on KTMTalk they discuss an oiled "sponge" trick instead of straight light grease. I think they use old air filters and cut them into donuts that fit inside the dust seal and oil them. Never noticed it posted here so I thought someone might be interested.

Sounds like a good trick, Meat. My mountainbike forks (RockShox Duke C) have such sponges underneath the dust wipers, you are supposed to keep them full of fork oil, filling them is part of the PDI. I wonder if this idea was ported from the mtb world?

[Luke]

Originally Posted by meat popsicle

Hey Luke,

Are you looking for info on the ASTM method?

http://www.tpub.com/content/engine/1...s/14105_37.htm

"The V.I. of an oil may be determined if its viscosity at any two temperatures is known. Tables, based on a large number of tests, are issued by the American Society for Testing and Materials (ASTM). These tables permit calculation of the V.I. from known viscosities."

Read your own links, man! From Peter Verdone:

VI = 100+(10^(LN((EXP(1.0727+0.6175*LN(cSt@100)+0.9744* (LN(cSt@100)^2)+(-0.3764)*(LN(cSt@100)^3)+0.04824*(LN(cSt@100)^4)))/cSt@40)/LN(cSt@100))-1)/0.00715

I'm just lazy.

So I looked up Mobil1 ATF, which goes for about $10/quart or half the price of Redline LightWeight. I don't get the attraction - $10 every 10K?

Hey, I use Rotella.

Seriously, I agree, there's no real benefit if you're going to use M1. The point is, you can use the same method to mix cheap oil too. If I were a tuner starting from scratch, I'd do it, because a then you're doing a few changes a day.

If you're tuning damper rod forks, you can also mix oils so that you only have to buy two kinds. Then when you settle on a good viscosity, use whatever oil matches it.

FYI, on KTMTalk they discuss an oiled "sponge" trick instead of straight light grease. I think they use old air filters and cut them into donuts that fit inside the dust seal and oil them. Never noticed it posted here so I thought someone might be interested.

IIRC, thumpertalk guys use gauze. Wrap around the fork legs a few times, then shove it in.

[meat popsicle]

Obviously I'm lazier Luke!

Now if I can finish these KSAs so I can get out to the garage to tear my bike apart some more...

[invader]

Amsoil's Shock Therapy Suspension Fluid #5 Light does have a viscosity that is comparable to the average of other 5W fork oils: 4.4 cst @ 100°C, and 15.7 @ 40°C.
Amsoil Medium #10 (10W): 7.3 @ 100°C, 32.1 @ 40°C.

http://www.peterverdonedesigns.com/f...ion%20oils.pdf

Forks typically operate at about 26°C (78°F) in 21°C (70°C) ambient temperatures...

[meat popsicle]

hey look a chicken!!!

[wrk2surf]

is it fighting with another one???

seriously if you folks are talking "fork oil" you are using a oil intended for a conventional old school forks... do yourselves a favor when buying for USD and get FORK FLUID...


look a jackalope

[ChrisC]

Originally Posted by invader

Amsoil's Shock Therapy Suspension Fluid #5 Light does have a viscosity that is comparable to the average of other 5W fork oils: 4.4 cst @ 100°C, and 15.7 @ 40°C.
Amsoil Medium #10 (10W): 7.3 @ 100°C, 32.1 @ 40°C.

http://www.peterverdonedesigns.com/f...ion%20oils.pdf

Forks typically operate at about 26°C (78°F) in 21°C (70°C) ambient temperatures...

Fuck me... a ancient thread resurrected, dealing with oil, and an Amsoil recommendation.

It's a goddamn trifecta.