Fork oil

[Guest]

Does anyone have any experience using ordinary multigrade 15W-40 motor oil in GS forks in place of special fork oil at 3 times the price?
Are there any issues doing it?

[salty_monk]

It doesn't react the same, it doesn't have the anti foaming agents in it I don't think....

It's not a bank breaker to get 15w fork oil... cost me about $7 for enough to do the bike. You only need about a 1/4 litre.
I used ATF to flush the fork cause it's thin & cheap at about $2.50 a bottle.

Dan

[rustybronco]

Does anyone have any experience using ordinary multigrade 15W-40 motor

No, but I do have experience with 20w and a dexron-III atf (7-8w) blend for almost two years now.

[Matchless]

Problem is I can only get 20W or 7.5W here at the moment. 10W or 15W is not available and I will have to order, suppliers are not interested. ATF is said to cause seal problems, such as swelling over time, but not sure on this either.
What you say makes sense, but I was wondering if foaming in a fork could be worse than in a modern engine which can have quite some heavy activity going on in it?

Rustybronco, I have seen the Clymer manual recommending an ATF and oil mix for the forks as you are using and then read that ATF should not be used on some seals.

[rustybronco]

but I was wondering if foaming in a fork could be worse than in a modern engine which can have quite some heavy activity going on in it?

Rustybronco, I have seen the Clymer manual recommending an ATF and oil mix for the forks as you are using and then read that ATF should not be used on some seals.

almost two years and no issues with it, running 10-11 psi in the forks.
atf has anti foam agents in it already. just don't use type "F" fluid, it has metal particles in it.
you could always mix the 20w and 7.5w fork oil 50-50 and end up with about 14w

more... http://www.thegsresources.com/_forum...057#post599057

http://www.thegsresources.com/_forum/showpost.php?p=599458&postcount=10

But after some experimenting, I have found that a mixture of 90% 15W fork oil and 10% "motor honey"

not a bad idea! (that brian is a smart fella)

[Matchless]

RustyBronco,
Thanks for that. I missed that thread on search and it basically gives me the answers I wanted.
I have just bought some Shell Advanced Fork 20 which is a SAE 20W-40 specially for forks and has seal swelling additive in it. I could then get it down to 15W by adding ATF, which I understand now is about 10W or slightly lower, but not sure, and retain the special properties.
That was very good information and a very informative thread for me!!
Thanks again.

[rustybronco]

fork oil=20w atf=8w
60(20w)-40(8w)mixture=15.2w if my math is good.

http://archive1.gwrra.org/discus4/messages/90752/139997.html?1169311741

In fact all the data so far seems to indicate that todays ATF is a viable
substitute for fork oil.

Here is a short table comparing the viscosity and Viscosity Index of several
brands of Dexron III - Mercon ATF to some popular brands of fork oil.

Brand\Temp 40 C 100 C VI
Esso 37 7.1 ??
Valvoline 36 7.7 190
Amsoil 36 7.5 182
Exon ?? 7.5 ??
Chevron 36 7.2 172
BelRay 15 59 7.6 100
Spectro 15 47 7.2 100
Honda 10 35 7.4 200

well, I now know all my brain cells aren't dead (7-8 wt)

just blend the two around to your liking!

[salty_monk]

Yes definitely no problems with blending different weight fork oils, done that before on a bunch of mountain bikes with similar setup.

I just use ATF for flushing but I don't see it doing any harm as a blending agent.

Dan

[Nessism]

Suzuki changed their fork oil recommendations over the years but for quite a few years they recommended a 50-50 mix of 20W oil and ATF.

[lurch12_2000]

I bought 20w fork oil at one dealer for $5.50/quart and later bought 10w fork oil at another dealer for $7/quart. Not sure why everyone is buying the expensive stuff or paying so much. My 1100's use 16oz total per change. That means I get 4 changes out of the 2 quarts I have which equals a little over $3 per changing (about the same as a quart of motor oil or ATF).
I decided to drain out the 20w and replaced with 10w to see if there was any difference in feel on my G. Then I just mixed the half quart of 20w and half quart of 10w that were remaining and now I have a quart of 15w, good for 2 more changes and a good compromise on how the fork will feel.

[Matchless]

It sounds good, as nothing beats practical experience. I was even going to try the 20W to get the feel of the damping.
RustyBronco, as you say, now it is even easier to blend whatever weight is best, so maybe my luck that the 20W is available here and easier to thin down with ATF than thickening up. Thanks for the formula, I will check what type of ATF I have tomorrow, but would guess the weight to be very close or the same to those you gave.

Thanks guys!

[Nessism]

Someone here posted this link a while back that compares various oils and brands of fork oil for viscosity. Lots of good info here... http://www.peterverdonedesigns.com/lowspeed.htm

[Zook]

ATF weights vary a bit, some are 7wt, some 10, some 8.
Seal swelling agents IMO shorten seal life. IMO they are like stop leak fir radiators. Doesn't really fix the problem and can cause more.

[Suzuki_Don]

Don't mean to hijack here Andre. But a question still on forks. I have just received my 650 forks to go on the GS550B and they have the capability for air pressure in the top caps. As I have never before had a bike with air in the front forks can I receive some advice on how much pressure to run with and any procedures to end up at the correct pressure and how this system actually assists the normal oil damped forks.

BTW that software you put me onto works brilliantly. Thanks for sharing.

[rustybronco]

BTW that software you put me onto works brilliantly. Thanks for sharing.

Thread Hijack!!!
Now you piqued my interest. what software if you can say?