Kawasaki ZX600 Fork Oil Question

[Joe Nardy]

I know it's not a GS but I'm helping another member replace fork seals on his 1989 Kawasaki ZX600. The recommended fork oil in the Clymer Manual is 10W20. I'm hoping someone here has experience with ZX600s and has a good recommendation for fork oil weight.

Race Tech recommends 15W. that sounds like a good ballpark for an '89.

Thanks,
Joe

[focus frenzy]

ummmm yea, what they say.
what was the question again?
what are the factors?
thinner oil faster action less damping
thicker oil slower action more damping

[trippivot]

I like 15 weight fork oil. it will be nice.

some times I will mix 20 and 15 in equal parts. always fork specific oil.

the thing about fork oil is the resistance to foaming.

avoid A.T.F. or motor oil for this application.

[Nessism]

I like 15 weight fork oil. it will be nice.

some times I will mix 20 and 15 in equal parts. always fork specific oil.

the thing about fork oil is the resistance to foaming.

avoid A.T.F. or motor oil for this application.

I've used both motor oil and ATF before in forks and never noticed any difference between that and fork specific oil.

[Steve]

If I am understanding my oils correctly, 10w-20 would be motor oil. Do they make multi-weight fork oil?

If it is motor oil, the 10w part is the viscosity when it's cold. Specifically at 32 degrees, I think, but at least when it's no warmer than room temperature. The 20 weight is only acheived when it gets WARM, specifically around 200 degrees. I would not be surprised to hear that MX or enduro racers get that warm with constant movement like they encounter, but do street forks get that warm? If not, then it would never get to the 20w viscosity.

I would suspect that for most street use, a single-viscosity oil would suffice, and 15w is a good place to start. Just remember to put in the proper amount, then check the level. Unless you have completely disassembled the forks and cleaned them out, there will be some old oil left in the tubes. How much? No way to tell. That's why you measure the final level after adding oil to make sure you don't have too much in there.

.

[Joe Nardy]

If I am understanding my oils correctly, 10w-20 would be motor oil. Do they make multi-weight fork oil?

If it is motor oil, the 10w part is the viscosity when it's cold. Specifically at 32 degrees, I think, but at least when it's no warmer than room temperature. The 20 weight is only acheived when it gets WARM, specifically around 200 degrees. I would not be surprised to hear that MX or enduro racers get that warm with constant movement like they encounter, but do street forks get that warm? If not, then it would never get to the 20w viscosity.

I would suspect that for most street use, a single-viscosity oil would suffice, and 15w is a good place to start. Just remember to put in the proper amount, then check the level. Unless you have completely disassembled the forks and cleaned them out, there will be some old oil left in the tubes. How much? No way to tell. That's why you measure the final level after adding oil to make sure you don't have too much in there.

.

Steve,

The Clymer manual doesn't state anything other than 10w20. I have never seen multi-viscosity fork oil so that's why I asked the question. I know 15w is a good guess for 80's damper rod forks but was hoping I might find someone here who has personal experience with this or similar Kaws. We're going to use Bel-Ray 15w fork oil and see how it works.

Thanks,
Joe

[Billy Ricks]

My old T-305 called for 10W20-30. Back in the day you could find that viscosity.

[Nessism]

Bel-Ray fork oil is thicker than some other brands. I think you would be better off with 10W if using Bel Ray.

As an aside, I had a '92 ZX6 for a short while and the front end on that thing was a jack hammer; poor compliance due to high compression damping. Not sure if the '89 is different or what but lightweight fork oil is rarely a problem unless you are heavy and ride hard over rough pavement.