Fork Oils

[89katana750]

According to my haynes manual it says to use SAE10 Fork oil. However a friend of mine who has an 1980 GS 850 can use SAE10, SAE15, SAE20 and as a supplement can also use dexron ATF. Would the early katana 750's be able to handle the dexton ATF?

[Black_peter]

You can go up to 15, I did.
The oil is forced through ports to control the speed of the fork compressing/rebounding. Those ports are adjusted with the little dials on the end caps ( the 1-2-3)
As you dial it up the post gets smaller and the oil
can't get pushed though the ports as fast..
By uprating the oil, this has the effect of making
1 feel like 2 etc. So instead of 123 you have 234.

Going to 20 would be like 345.
Question is are your forks too soft?
("Bouncey")
Or are they undersprung?
(Bottoming out)
Suzuki softened the springs for the Kat.
So for sport riding they are undersprung.

For the price, fork oil isn't very pricey.
You don't change it often..
ATF could work, but is it worth the experiment?

[ThAzKat]

I would only reccomend the dexton ATF for emergency use. MO

[89katana750]

My forks do seem like they are undersprund. I feel like everytime I go over a big bump the forks dive too much in. Switching from 10 - 15 the forks would be stiffer right? (depending on what the dials are set up for).

if they are boucny would that mean the oil needs replacement or that there is less than normal oil? its been 20,000km since the oil has been last changed.

[ThAzKat]

check this out, for street use race tech says a 180 rider needs a .928kg/mm spring rate in the front and the factory is .629kg/mm rate stock.
That is for a 89-97 750 Kat

http://www.racetech.com/evalving/SpringRateCalculation/dirtspring.asp?brand=Suzuki&yr=89-97&ml=GSX750F%20Katana&formuse=form1&SpringType=Fork

[89katana750]

factory is set very low. im a light weight though, 165lbs, hehe. But I ride with a lot of gear all the time probably making it 190lbs.

thanks for the help

[The CyberPoet]

My forks do seem like they are undersprund. I feel like everytime I go over a big bump the forks dive too much in. Switching from 10 - 15 the forks would be stiffer right? (depending on what the dials are set up for).

Springs weaken with time, and my suspicion is that you are still on the original springs -- on a 16 year old bike. Thicker fork oil will reduce the dampening, which means while your forks won't compress as much (because the oil will take more of the load), they also won't react to small bumps as well and the ride may turn harsh.
KNOW THIS: because of the long wheelbase, heavy weight and sport-tourer design, the front end of a kat will normally dive far more under braking than a comparable true sports bike. This is intentional and designed that way to help reduce fatigue over long trips.

if they are boucny would that mean the oil needs replacement or that there is less than normal oil? its been 20,000km since the oil has been last changed.

The oil should be replaced every other year under normal circumstances. Whether that 20,000km was in 3 months or 3 years is the important part, usually, unless there are damages to the oil seals (which would let it leak).

Cheers
=-= The CyberPoet

[ThAzKat]

Cyber what if you have the frontend off the ground alot?

[The CyberPoet]

Cyber what if you have the frontend off the ground alot?

See my response in this thread:

http://www.katriders.com/forums/viewtopic.php?t=3946

Cheers
=-= The CyberPoet

[ThAzKat]

I should have put a <laugh> behind that post sorry bro, and true that. So that explains alot about the weak fork springs and why the are dialed into a lite rider. Thanx Cyber

[tzortn]

... Thicker fork oil will reduce the dampening, which means while your forks won't compress as much (because the oil will take more of the load), they also won't react to small bumps as well and the ride may turn harsh...

Just as a clarification: Thicker fork oil will increase the damping (not dampening, sorry CP this is a personal peeve of mine). Thicker fork oil will stiffen the front end and make it less responsive (like CP explained).

[89katana750]

Now im thinking of just sticking to the 10 wieght, I don't want the ride to be "harsh". Smooth was what I was going for.

[The CyberPoet]

...increase the damping (not dampening, sorry CP this is a personal peeve of mine).

Thanks... I actually appreciate that you've pointed that out to me in the past (and now), in as much as English is my second language; it's a mistake I make (and consciously thought about late last night -- as in "is it damping or dampening?" but just went with it).

Cheers
=-= The CyberPoet

[tzortn]

Thanks... I actually appreciate that you've pointed that out to me in the past (and now), in as much as English is my second language; it's a mistake I make (and consciously thought about late last night -- as in "is it damping or dampening?" but just went with it).

Cheers
=-= The CyberPoet

No problem. It is amazing how often that mistake is made. I hear engineers say it all the time.