Harsh CR fork...yes, again

JTT

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#1
I've been struggling with this fork for some time now. I am a 185lbs, MX vet rider, '00 CR250. I have had the forks professionally revalved and resprung with .45 springs. Oil level 400cc.

The fork is better than it was, but still harsh. When compressing suspension (bouncing by hand), it seems that the first 1/3 of travel is good and smooth, then it "ramps up" rapidly and is very difficult to compress any further by hand. It almost feels like a hydraulic lock, although, when riding, this is obviously not the case, as fork does move on large hits.

The suspension company I was dealing with doesn't seem to have any real answers (don't even need to say it :( ).

I have tried the lighter springs, lighter midvalve valving (as per suspension tuners instructions), but still no success. Any suggestions would be appreciated as I am at a loss :think

The other issue I wanted to ask, was how critical and what roll does the oil level in the cartridge play?

I am thinking....Too high, the chamber spring would bottom out and there would ba a hydraulic lock in chamber. Too low and the effectiveness of this chamber spring would be lost. Input anyone?
 
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#2
Give all the specs on front valving and also how the rear is set up and will try to help, did the suspension company just do a revalve or did they use different pistons and if so how big are the ports. Need to know the whole story before a good evaluation can be made and the proper recommendation made.
 

JTT

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#3
It was just a revalve of the stock pistons. The rear is set up with a 4.95 spring. I am reluctant to post valving specs here (don't want to cause friction), so check your PMs.

Thanks for your help Rob, look forward to hearing from you.
 
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#4
JTT,
The oil in the inner cartridge doesn't have a "level" or height per se. If you correctly bleed and assemble the inner cartridge, then the oil volume will be constant and correct. The compression piston assembly is designed in such a way that the spring can only be compressed so far before a relief is uncovered by the bushing piece. This action will set the "level" (volume) of the oil in the cartridge. There is a possiblilty that the cartridge is not filled with enough oil to properly assemble it or that it wasn't blead correctly. This would prevent the spring from creating the proper pressure in the cartridge. I can't say I know if this would cause the problems you are experienceing. However, if the shop knows what they are doing, then the assembly proceedure shouldn't be an issue. What I find interesting is that I've spoken to many people with late model CR250s that are complaining of the same problem and I haven't heard of anyone discovering the reason for these simptoms.
 
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JTT

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#6
Bud-Man, thanks for the reply. So theoretically you could fill the cartridge to the top, then insert the basevalve, allowing oil to simply overflow form the cartridge without any complications (other than obvious mess ;) )?

I know the shop manual gives a range of oil height (from the taper in cartridge), and the suspension builder I used gave a specific oil height (above this taper)...maybe this is just to avoid the mess and make it easier to install basevalve without too much pressure needed to get to the threads?

:think I suppose that any oil getting blown past the "relief" would simply take up space in the main body of the fork and not really be an issue. I was nota ware of this "relief" before. Thanks for making that clear.
 
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#7
JTT,
No problem! Glad to be of assistance. Basically, yes you could fill it to the top. Although you would have a hell of a time getting the base valve assembly into the cartridge and it would make a terrible mess. If you look into the cartridge, you should see a step about 6" from the top. This is where the cartridge steps down to the diameter of the rebound piston. If you fill the oil until it is about 1/4-1/2" above this step, you should be fine. (This assumes that you have already pumped the damping rod several times to release any large air pockets under the rebound piston.) This will provide enough oil in the cartridge yet minimize the struggle to assemble (and the mess). You will still need to pump the damping rod about half way, 10 times to move any small air bubbles above the compression piston so they can be carried away with the excess oil. Now compress the damping rod fully and all the excess oil and air bubbles will pass through the relief. This last step is what actually sets the oil level or volume in the inner cartridge. One final thing: flip the cartridge assembly over for a few minutes and let the excess oil drain out so it wont mess up the oil level in the outer chamber. Hope this Helps.
 

John Curea

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#9
JTT
I found this old post from Jeremy, its a pretty cool...........



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Posted by Jeremy Wilkey on 07-12-2001 03:11 PM:

Try this.. It's for the 47mm CR 250 but it works the same..

Instructions for 2312 Twin Chamber fork valve installation and service.

Disassemble forks completely:

Valving components.
-Remove fork cap.
-Pour oil out of inner chamber.
-Taking a 21mm socket (Impact style) and an impact wrench remove the base bolt and rebound adjuster assembly. Use short bursts and not long durations of RPM as this can damage the components.
-Using a slot tool, remove the clicker bolt from the rod end.
-Using care remove the slot tool from rod end and let the rod return against spring tension.
-Remove the fork cylinder.
-Remove fork spring by sliding out the top.

Seal and tube dissembnly:
-Using a subtle blade (Flat but small screw driver) remove the dirt scraper. Don’t pry as it may mar the forks appearance.
-Using a smaller blade remove the circlip that holds the seal in place.
-Heat the seal carrier or the portion of the tube uniformly so as to facilitate easier bushing removal with out damage.
-Using quick but not forceful hits drive the tubes apart. (Speed is more important than force; never yank at the end of the stroke.) Use the quick momentum to drive the tube off. Failure to do as described above often results in bushing damage.

Internal component disassembly:

Fork cylinder: The 2312 twin chamber style fork requires the rod to be removed from the cylinder to perform internal modifications to the active compression and rebound circuits.

-The rod has several major components on it. The jam nut that should be threaded off. Using your hands or shaft blocks.
-Then using a narrow wrench remove the oil lock that remains on the rod.
-Drop the rod out the bottom of the cartridge.
-The nut holding the valving components has been staked from the factory and needs to be ground flat past the edge of the stake to remove the nut and separate the valving and piston. (Prior to the grinding process pack the orifice with grease to prevent grinding chaff from entering and being lodged in the internals.)
-After removing the stake the edge of the nut needs to be radiused of its metal bur that develops during grinding. (This bur may come free during fork use and causes numerous problems.) A polishing wheel such as cratex works very well and leaves an excellent finish. Be very careful to maintain proper shim and piston orientation during removal. Also note that may times small spacer shims are placed under the post spacer, or valve these are easily misplaced and will dramatically impact fork performance.
-Now that all the components are free of the stem radius the first thread to prevent thread wear during reassembly.
-The passive valving (base-valve, or foot valve) needs to remove. The nut holding the valving components has been staked from the factory and needs to be ground flat past the edge of the stake to remove the nut and separate the valuing and piston. (Prior to the grinding process pack the orifice with grease to prevent grinding chaff from entering and being lodged in the internals.)
-As a precautionary measure we recommend that holding the whole assembly in a rag protect the seals of the cylinder, as you grind the nut stake off.
After the nut and valving has been removed you will need to radius the first thread in the same manner as the active stem. Proper orientation must be maintained to insure the components are assembled properly.
-Wash and clean all components thoroughly before preceding any farther.

Assembly of fork tubes.

-Place the axle bracket in a vise and firmly tighten down.
-Placing a bag over the tube lube the seal and install the dirt scraper. (Remember that seals always work with pressure so if orientation becomes unclear use that as your guideline.) Install the circlip, oil seal, and backup washer. With round edge toward the seal. Bushing outer and then bushing inner. (After the oil seal is installed remove the plastic bag.)
-Use a 47mm seal driver to drive the seals and bushing into the seal carrier. Install the circlip and then install the dirt scrapper.

Assembly of the Active compression and rebound damping.
-Build the stacks specified and then install them on the stem. By very careful not to misalign any washers or components as they could be permanently damaged by doing so.
Double-check all components for proper assembly.
-The cartridge seal in the end of the fork cylinder is very high tension and requires that the seal be protected during reassembly. Wrap the threads in Teflon tap. Cover the threads but don’t apply to many layers. The end of the threads to the chrome should have a uniform layer. Push any extra below the chrome edge to prevent them being caught in the seal.
-Place the rod back into the cartridge. And use a 10mm T handle wrench to install the rod by turning and lightly press in the rod into seal and out the bottom.
-Reinstall the jam nut firmly bottoming it onto the rod.


Assembly of the Passive compression valving.
-Install the valving components on the base-valve stem add a drop of blue loctite to the threads. Tighten the nut down firmly but do not over or under tighten. If you’re revalving build the necessary components and stacks.

Assembly of the cylinder.
-Place the cylinder upright in a vise. With the rod fully extended fill the cylinder to the shoulder. Bleed the cartridge by running the rod through its stroke till the action is smooth and consistent. Recheck the oil level. Make sure it is above the shoulder slightly but do not overfill, as it will make the compression valve nearly impossible to install.
-Place the compression adjuster in the cylinder and compress it till you can thread it into the cylinder. Tighten down lightly.
-Compress the inner rod completely and drain the excess fluid out.

Installing internal components:

-Install the spring in the fork tube.
-Place and align the fork cylinder in the tube.
-Using the slot tool feed the rod throw the end of the fork using your finger, and then capture the end with the slot.
-Place the indexed d-rod in the rod.
-Place the 21mm bolt on the end of the rod and tighten down till it bottoms out. Then tighten the jam nut down. Torque sufficiently.
-Grease the threads before removing the slot tool. Carefully remove the slot tool and start the threads by hand.
-Using an impact wrench tighten the bolt into the base using short bursts to tighten into place. Then use a socket wrench to torque to final torque.
-Place the fork upright and fill with fluid. Normal volume is 375cc.
-Bottom fork cap to the tube but do not tighten. The top triple clamp is responsible for keeping the cap on.

Reset your clickers and enjoy!






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JTT

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#10
Thanks KXVet, I printed that one the first time I saw it...valuable resource ;)
 

MACE

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#11
Like I Said Before - I Don't Knowa Showa...

But on my KYBs I found the "hitch" in the fork stroke was actually the rear suspension topping out. Try throwing a tiedown over the seat to the rear tire to preload the rear and THEN push down the fork to see if there is really a "hitch" in the stroke.

Next remove the fork springs and move the fork through it's travel (axle in place) to see if you can feel any binding.

YIKES the USGP is starting......
 

nephron

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#12
JTT

In the last few pages of DirtRider, you will find a "new product" review of replacement forks/shocks specifically designed for the aluminum-framed CR250's of late. I don't recall the name of the company, but the designer spent many hours refining his product. He also explains the etiology of the problem. Take a look. Your answer is in there. However, it's vague enough that you'll probably have to buy his setup to fix it.;)
 
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#13
Try lower the oil-level to 370 - 380 cl and use 2.5W or 5W forkoil.
The oil-level seems to affect only the lower half of the stroke.


(CR250 -00)
 

slideways11

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#14
JTT I also went through all the problems batteling harshness in my 01cr250 and nothing I did seemed to help much. Not all the harshness is generated in the front end ,the rear shock fades really bad as it gets hot just compounding the harshness you feel in the front. I ended up sending the shock and forks to MX-Tech for total revalve and whatever it takes to make them right. The bike works so much better you won't believe it.
01cr250,02yz250@125