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Fork oil. Can it lose viscosity?

Old 06-04-2011, 04:34 AM
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Fork oil. Can it lose viscosity?

As the title says, can fork oil get lighter with age?
I replaced the compression valves and springs with Racetech gear and used 5W oil as per the specs. When the mod was completed, the front end end was nice and firm and I set the rebound so as to to get that very slight dip when bouncing the front. Everything I have ever read about suspension said this was the proper technique and the bike handles beautifully.
The other day, I was discussing rebound with a friend and went to show him how I set mine up, but the front end was very "squishy" , very much like the standard forks. The rebound "bounce" was very pronounced which surprised me a lot. The bike has done about 30,000 klms (20,000 miles?)since I did the front end so it was due for a change anyway, but the reduction in damping was surprising.
When I did the original work at 24,000kms, the original Honda fork oil came out like a brown sludge. It just seems odd to me that oil could get thinner instead of thickening up with age.
Anyone else struck this situation?
I did not do the rebound damping rod mod where you remove the taper.
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Old 06-04-2011, 04:49 AM
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Well... A simple clue is the intervalls on changing your engine oil... The fork oil isn't having an easy life either... That and the fact that you are supposed to "check" the suspension at the service every 12.000 km...

Ok, agreed "check", doesn't mean replace the oil, but I'd say rule of thumb is every other year or a reasonable amount of miles/km, say every time the "big" service comes around, at 24.000 km is the most I'd ride without swapping the fork oil... And I'd probably prefer to keep it at 12.000 km to be honest...

The first step in ageing is the "brown sludge"... The second is when the oil separates into thin oil on top, and thick sludge in the bottom...

Then you get the "wet noodle" feeling you have, and at that point just swapping the oil becomes a bit more complicated as you probably need to disassemble the fork and clean it pretty throughoutly to have all the ports working at peak efficiency...
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Old 06-04-2011, 05:53 AM
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Again, spot on. What surprised me most was that the oil seemed to "collapse" in a short period. I am a bit pedantic when it comes to the suspension, as basically it's the only mods I have done. This was more a question out of curiosity for furthering my knowledge. The forks will be dismantled shortly due due a blown seal so the problem will be resolved.

I have always had the philosophy that good suspension will beat more horsepower any day. It's no good having 200rwhp if you can't get it to the ground.
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Old 06-04-2011, 06:06 AM
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Originally Posted by Fozzy Bear View Post
I have always had the philosophy that good suspension will beat more horsepower any day. It's no good having 200rwhp if you can't get it to the ground.
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Old 06-04-2011, 09:12 AM
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theres a reason race bikes get new fluid for ever race.
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Old 06-04-2011, 09:53 AM
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Originally Posted by Fozzy Bear View Post
I have always had the philosophy that good suspension will beat more horsepower any day. It's no good having 200rwhp if you can't get it to the ground.
I'm another one that truly believes this.

It also goes for the brakes..... kind of hard to stop if the wheels are not on the ground....
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Old 06-06-2011, 11:14 PM
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Originally Posted by Fozzy Bear View Post
I have always had the philosophy that good suspension will beat more horsepower any day. It's no good having 200rwhp if you can't get it to the ground.
Amen to that.....I have a buddy who rides a 20yr old GSXR on the track and beats just about anything with a whopping 86 hp...
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Old 06-07-2011, 02:49 PM
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Well, the fluid in forks does not break down quickly as is suggested here. The fluid needs replaced mostly because of particulate matter. If you use a quality oil (the stock Honda SS grades are not real good, the Honda Pro is) then you will be fine for many 1000's of miles. I normally change the fluid in my forks every 10,000 miles or so.

Something else to note: I've never found the "bounce" technique to really tell you anything at all. Sure, most of the so-called-pros do this to setup bikes, but I've found that it really only gives you a very gross adjustment. By very close I mean barely in the ballpark. Heck, you aren't even on the motorcycle when bouncing it so how can it possibly give you an indication of what is happening when you are? No, the only way to properly setup your suspension is to feel what it's doing while you are riding and adjust to compensate for any ill-effects.
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Old 06-07-2011, 07:02 PM
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I prefer to change fork oil every 6-8,000 km. If you wait for the oil to break down and get contaminated with particles, it is too late. You are wearing out parts for nothing, not withstanding the degrated performance. If you do a lot of track days, then you may want to increase the interval. Oil is like bread, always best the first day. It is cheap insurance and simple to do. I do it in the off season i.e. winter. For Aussies, you will have to pick a bad weather spell since you don't really have a REAL winter. Consider it rootine maintenance.
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Old 06-08-2011, 12:50 AM
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Originally Posted by JamieDaugherty View Post
Well, the fluid in forks does not break down quickly as is suggested here. The fluid needs replaced mostly because of particulate matter. If you use a quality oil (the stock Honda SS grades are not real good, the Honda Pro is) then you will be fine for many 1000's of miles. I normally change the fluid in my forks every 10,000 miles or so.

Something else to note: I've never found the "bounce" technique to really tell you anything at all. Sure, most of the so-called-pros do this to setup bikes, but I've found that it really only gives you a very gross adjustment. By very close I mean barely in the ballpark. Heck, you aren't even on the motorcycle when bouncing it so how can it possibly give you an indication of what is happening when you are? No, the only way to properly setup your suspension is to feel what it's doing while you are riding and adjust to compensate for any ill-effects.
Well, I never said it breaks down fast... I suggested 12.000 km or 7500 miles or twice that as a reasonable intervall... Your 10.000 miles is in that ballpark, it's just that for me to remember when to do stuff I do it all at one time...

What I do think we can agree on is that once the oil does start to degrade it goes from bad to worse pretty fast...

Bouncing is just basic, ballpark setup, agreed... But it gives you a pretty good idea if the damping/rebound you have dialed in is ballpark right for the preload... And then you obviously need to go riding for tuning it...
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Old 06-08-2011, 05:14 AM
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With all of the forks that come through my shop it's only the ones that have 20k or more on them without any servicing that show any appreciable problems. It's nice to hear you guys are taking care of your bikes. To err on the side of caution is certainly a good thing!
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