Motor oil for fork oil?

[Guest]

Folks,
The service manual says use a 50/50 mix of motor oil and ATF as fork oil. I've haven't wrenched much on older bikes and wasn't sure if this was something that is just disregarded now that we have high quality fork-specific oil for sale everywhere. Should I just grab some 15w fork oil or stay true Suzuki's recommendation from '79?

[chuck hahn]

If you want to but its like 16 bucks a quart. So for like 7 bucks you can make a half gallon which will probably last you and all your buddies a lifetime.

[chuck hahn]

Straight 30 WT cut with the ATF will yield something like a 15 weight factory fork oil If I am remembering then other gurus formulations right.

[JTGS850GL]

I'd use an oil designed for use in the forks. Many better options available today then in 79. The new fork oils are developed specifically to produce less foaming. and you won't have to try to figure out what your final weight is. My 82 manual recommended a 15W fork oil. Just paid $7.50 for a liter.

[Steve]

There might be some purists that still follow the book, but with fork oil so much more easily available now, most of us just use fork oil.

The viscosity used will be personal preference. Those who are more agressive riders or have an enhanced gravitational attraction might go for 15w or even 20w oil, I happen to prefer 10w. Keep in mind that one manufacturer's 15w is not necessarily the same as another, so if you decide that you need to change viscosity, stay with the same manufacturer for consistent results.

.

[chuck hahn]

$7.50!!!! Heck then last Q of Bellray I looked at said 16 and change!!! Nah..I had a half quart of ATF and some oil so I made the Manuals concoction. No problems for me so far.

[Bonehead]

At the shop, the guys always put in straight ATF. Always on a Harley though, dunno if it would differentiate with our air cooled beasts

[derwood]

just grab some 15w fork oil

factory suzuki manual says fork oil (1984)
racetech says fork oil
progressive suspension says fork oil

fork oils have been developed for your benefit, you can chose to ignore this and save yourself 8 dollars,

big factor for rebound control is fork oil viscosity, I like suspension tuning, keeps the wheels in contact with the road, this provides the means to control the motorcycle

Adjust the sag of your suspension by playing with spacer length, maybe try cutting those ancient fork springs, better yet replace them......... how about cartridge emulators?? Despite the cost I have not regretted suspension upgrades.
You gonna ride this thing or just look at it? ATF? don't waste your time.

10w in the hawk, the rest are 15w, Gonna try 10w in the 1150, still playing with the new springs and emulators
(surprise the harley came with cartridge emulators from the factory)

[jwhelan65]

I use 30w fork oil in my 700

[rustybronco]

I use a 50/50 mix of Dexron and straight 30 wt engine oil.

[hjfisk]

I run 30 wt . fork oil in all my bikes. But I am also a heavy weight and ride aggressively.

[TheDuke]

Seems that most use fork oil. That is what I figured. I just wanted to make sure that forks designed to work with the 50/50 mix would not be hurt by the new stuff. I will grab some 15wt fork oil ASAP, I have some new Progressive springs on their way to me as we speak. Thanks for the advice guys.

[eil]

Suzuki has a part number for 15wt fork oil, 16 oz: 99950-06080. When I do a search for this, I find lots of places apparently selling it for under $4. I suspect that actually trying to order it wouldn't work, or that shipping would shoot the price well over what it costs in the store. Maybe someone else can give it a go and report their results.

[chuck hahn]

Dealership I was in looking at the Bell Ray stuff must have really been price gouging then at $16+!!!!!

[Brendan W]

Came across a thing called the Refutas equation for calculating the viscosity of a blend.
I want to try a heavier 20W fork oil which typically is 65/12 cSt at 40/100 C.
I looked at a 10W40 motor oil at 97/15 and an atf at 36/7 to cut it with.
You might think that a 50:50 mix would put the finished viscosity bang in the middle but it's not that simple. The calculated viscosity for the 50:50 is 58 cSt at 40 C , only about a third the way between the atf and the 10W40 and about halfway between a 15W and 20W fork oil.
The next try was 1/3 atf and 2/3 10W40 which comes out at 64 cSt , close enough to the 20W fork oil.
I can't find reliable info about using this method for multigrades but am going to give it a go.