David, great to see you go with the revalve. I'm curious about your 10wt oil comment. I realize you have an SF and not the dirt model, so I'm not up on the oil recommendation for your bike...but 10wt sounds quite high. Did John recommend 10wt for a revalved fork for the SF? My S model uses 5wt for the OEM fork oil and for the Race Tech revalve. I've noticed something in high end dirt motor suspensions and high end MTB forks. They almost always use 5wt or 7.5wt suspension oil. Usually you only see 10wt or greater oils in lower end ported orifice dampers...like what's on the KLR series. Shimmed dampers don't usually like heavier oil...kind of defeats the purpose of the shims. Yes there are exceptions, but 5wt/7.5wt is the general rule. I'm just curious, and not challenging what you're doing.

McNutts, on the oil viscosity, you could go lower, like to 2.5wt to try to get more flow through the OEM piston, but then the shim stack probably won't be close to a good match, and the rebound will probably be off. Oil level can be a very good tuning tool to control bottomout, but you weigh about what I weigh, and the stock springs are just flat too soft for us. If you were thinking about going to heavier oil than the stock 5wt, that only aggravates the limited flow through the OEM compression piston.

 

The little bit I know about suspensions has shown me that THINNER oil, in an appropriately designed system, performs better than an inadequately designed system with thicker oil. Thicker oil doesn't flow as quickly, which makes any system seem "stiffer", when, in reality, it isn't stiffer as much as it is SLOWER. SLOWER moving suspensions don't react as quickly, which is almost always NOT what you want. The only time I've ever seen SLOWER to be preferable is on rebound...and, maybe to some extent during the compression stroke on high G-Out's.

Just don't be fooled into thinking thicker oil is a fix, if the real problem is an inadequately designed system...because the SLOWER movement of a thick oil is harsher, and it's easy to confuse "harsher" with "faster", because "harsher" is less control...and less control fools the brain into thinking it's moving faster. Timed laps, especially when combined with Heart Rate monitoring, is the only way to know if your suspension is performing better, worse, or the same after an adjustment. It's surprising how often people can be fooled unles they are doing timed laps on the same course.

 

I have just had my bike since the fall. Being a new rider I haven't pushed it hard enough to find the poor fork performance other than the spiking over repeated quick hits which is quite disconcerting. Maybe I'll throw some thinner oil in there for now to try to quell this.

 

If you try 2.5wt oil, let us know what happens. I don't think anyone has tried this. I think the rebound will be too fast, but like I said...I don't think anyone has tried 2.5wt in the fork.

 

totally agree

 

Yes He DID recommend 10 wt oil. I told him I did not want take the forks off and how I was going to change the valves. John also said the oil that comes in the forks is good stuff. I have no idea. I have replaced quite a few fork seals by just taking the bolt out of the bottom with an impact wrench and had no trouble. I know its not the best way but it works for me.

I asked John a LOT of questions. I paid for the valves and the info. I asked a lot about the rebound valve too because I did not touch them and I think they are a little soft.

I know now how the bypass screw works, so the more its in, the more rebound damping I should be getting. Not a lot of difference don't get me wrong. This is where understanding how it works can help me work with it.

I was told in college that automatic transmission fluid is 5 wt HIGH detergent oil dyed red. I still believe that and use the stuff for a lot more than transmissions. I did not put it in my forks.

The thin oil thing is correct to me. As long as the system is designed for it. I also think the forks would be a good place for synthetic because it does not change in viscosity from like 40*f to 80* f. $20.00 a quart isn't bad since I would only use one quart in my bike.

Changing the oil is an easy and important way to tune the front suspension. I really don't know how to do it with out taking the forks all apart because I have not done that YET. If you look at Ohlins website or a couple of the other suspension places, everything is designed for 10wt.

No test drive today, I am writing this while my truck warms up for work its 3*f right now.

I am glad I have you folks to shoot the bull with while the winter s l o w l y passes by.

David

 

David, on the fork oil issue and the KLX250SF suspension in general I figured I'd better read up a little about your model. In places where I could find detail about the SF's suspension, it stated that it has different damping and a different oil level to stiffen the suspension compared to the dirt model which would be logical. The fork is still the KYB 43mm type on the dirt model, but also with reduced travel. The type of use and reduced travel changes the damping demands on the shim stack, springs, etc. The "ONLY" reason I'm mentioning this is so that people with dirt models who want to mod their suspensions may want to consider that David's model's mods may not be a 100% match. If John recommended 10wt for the fork, I think it would be because the SF probably doesn't need or want the super fast and softer response needed by a dirt model, but I would think the revalving and new shim stack would be designed to handle that all by itself without having to go to thick suspension fluid. I can just about guarantee that going to 10wt oil in the KYB fork on our dirt model with either OEM or revalved damping might verge on extreme harshness. One small but important unknown here is the exact damping package that John uses for the KYB fork in the dirt and SF models. I'd think the SF will have different damping for the reasons already stated above, but I'd be surprised if John's dirt model damping would use 10wt for the ideal suspension fluid...but...I haven't used Moto Pro's revalve kit...only Race Tech's.

David, on the Ohlins discussion we were having about 10wt oil, I researched a good bit of info about Ohlins forks in general, and it still looked to me like the predominant oil in the dirt model forks is 5wt. Some general comments on Ohlins forks and Ohlins oil stated 5wt for their cartridge forks and 10wt for conventional and other forks. That statement for "conventional" forks is often related to the more simple ported orifice forks, but it didn't break that down. Regardless, we are talking about a KYB fork on our KLX's and they use a shim stack, not just ported orifice design. Unless John's valving and shim stack are dramatically different, I'd bet the dirt model fork will always work better with 5wt or 7.5wt fork oil.

David, on the fork oil you left in the fork, do you know what weight it is? I'd still be surprised if Kawasaki used something different from 5wt, but like I said, I'm not an SF guy. Anyone know what the Kaw specs state as recommended oil viscosity for the OEM SF?

As I mentioned ealier, I am not questioning David's mods here, but just remember that his SF mods may not transfer 100% over to the dirt model. I'm certainly no authority on this and probably have more questions that answers about some of this.

David, you were awfully lucky to get that compression valve unit out of the bottom of the fork without using the holding tool. They almost always spin because they have a fairly nasty coat of thread locker on the threads. For those not wanting to make a 1/2" drive 14mm allen tool on their own, Harbor Freight has a good useable set of large 1/2" drive allens for a good price.

 

OEM oil for SF is the same as for the S version: KAYABA 01 = sae 5 approx (I think 4'1W). Vary the amount, not the density.
It is very possible that the SF OEM specifications work better with a heavier weight oil (SAE10) and does not require quick work of compression and extension, focusing on the speed stiffness.
The friend John always recommends SAE10 to the fork, but I think it's specific to your system works well ReValver Ultra Max.
Currently I have installed your fork springs on the OEM oil. The result is very good, but I have to keep the compression clicks softer to roll over rocks and small bumps where rapid compression and expansion work is essential
For me it would be a grave error when installing a SAE10 ... just what I want is a job even faster.
I thought of a SAE 2.5, but I'm afraid mistakes and excessive force have rebound later.
I insist that the trials are with OEM valve, possibly with the Ultra Max SAE10 better go, I do not think John is wrong.

 

I went for a short ride today around the block. The bike rode better. I went over rail road tracks at good speed and the front wheel just absorbed the bumps instead of wanting to turn the handlebars. The adjuster screws were all the way out because that is where I had left them.

It used to feel like the back was too soft and the front way to firm, now they seem to be a lot more balanced. I could find no bumps that would jar me. I use the brake hose as a "meter" to watch and see how much my forks move up and down especially when I pile on the front brake.

John recommended #12 on a scale up to 13 for low speed compression damping. By weight the chart in the instructions was at # 5 or 6, so I chose #10

He aslo recommended #10 of 20 for High speed Damping. He looked up the oil and said he was out of 10 wt. I stuck with the middle of the road.

He also said to tune the rebound damping to use different weight oil was pretty much the only way.

I'm OK with the 2.5, or 5 wt oil, what ever is recommended, I was thinking more along the lines of shock assemblies not forks that all take 10 wt. I need to read up a little.

The bike rode great. I could tell the difference. Big bumps and RR tracks were "uneventful".

David

 

The manual says:

Push it as far as it will go in or out?