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  1. #1
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    Rebuilding a Curnutt Shock

    Never done it before. Wish me luck!
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  2. #2
    TNC
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    Looks a lot like a dirt motor rear shock. Are you just doing routine service or was there a problem?

  3. #3
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    It was bottoming out prematurely. Not sure why. Possibly the ifp had moved.

    I cleaned everything up, all looked ok. Refilled with Showa fluid and back together. The bottom out appears to be acting normal now. Time for a test ride!
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    Last edited by iheartbicycles; 07-11-2011 at 08:57 PM.
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  4. #4
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    Quote Originally Posted by iheartbicycles View Post
    It as bottoming out prematurely. Nit sure why. Possibly the ifp had moved.

    I cleaned everything up, all looked ok. Refilled with Showa fluid and back together. The bottom out appears to be acting normal now. Time for a test ride!
    Just got back from a test ride around the block. Rebuild worked and bike is back to getting full travel. I could have gone a little shallower on the ifp, but going to leave it for now and see how it goes!
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  5. #5
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    Nice! That was fast...

    Can you post up IFP depth & pressure (if you remember) for other Curnutt users that might try this?

    Out of curiosity, is that SPV?

    P

  6. #6
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    I am in the process of rebuilding it again right now. I decided it didn't have the end stroke ramp up I wanted. Currently the ifp is at 5" measured from the center divot in the ifp to the shock housing body. I am going to try out 5.25" and see how it feels. This is for a 3" stroke Curnutt.
    Last edited by iheartbicycles; 07-12-2011 at 09:38 AM.
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  7. #7
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    Quote Originally Posted by iheartbicycles View Post
    I am in the process of rebuilding it again right now. I decided it didn't have the end strike ramp up I wanted. Currently the ifp is at 5" measured from the center divot in the ifp to the shock housing body. I am going to try out 5.25" and see how it feels. This is for a 3" stroke Curnutt.
    Much better! I put the ifp at 5.3" and am now able to run ifp pressure at 60psi with bottom out at 1/2 way. This enables better small bump cOmpliance and good ramp up.
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  8. #8
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    I want to see some higher res images, especially of the ifp.
    my B+W landscape photos ....www.f45.com

  9. #9
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    The thing in the middle is the ifp.
    Attached Thumbnails Attached Thumbnails Rebuilding a Curnutt Shock-imageuploadedbytapatalk1310486393.351771.jpg  

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  10. #10
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    yep, the ifp pops out with some force when you add air to the chamber.

    I used Torco light RSF for the refill.
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  11. #11
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    Quote Originally Posted by Katana View Post
    yep, the ifp pops out with some force when you add air to the chamber.

    I used Torco light RSF for the refill.
    Forgot to tell you about that. Did you get your rebuilt??
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    I know this might be a PITA but how about a step by step guide with a description for each photo?? Im really keen to have service my Curnutt (done plenty of dhx coils but im a bit reluctant to rip into the Curnutt). I need some help on getting the IFP out, how much fluid and what weight to put back in and putting the if back in and what level to put it at.

  13. #13
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    Quote Originally Posted by allmountain76 View Post
    I know this might be a PITA but how about a step by step guide with a description for each photo?? Im really keen to have service my Curnutt (done plenty of dhx coils but im a bit reluctant to rip into the Curnutt). I need some help on getting the IFP out, how much fluid and what weight to put back in and putting the if back in and what level to put it at.
    Sorry, no step by step. To get the ifp out, just pump some air into it. Ifp depth depends on which shock you have and on personal preference. I recomend 2.5 weight oil.
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  14. #14
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    ive got the 9.5 x 3 on a 2007 fxr. Have you got guides for the ifp depth and oil levels?

  15. #15
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    Quote Originally Posted by allmountain76 View Post
    ive got the 9.5 x 3 on a 2007 fxr. Have you got guides for the ifp depth and oil levels?
    You're going to want the ifp depth around 5.3". Measured from the deepest ( center) of the ifp to the top of the shock body. I used a pencil, but any skinny tool should work.
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  16. #16
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    Quote Originally Posted by iheartbicycles View Post
    You're going to want the ifp depth around 5.3". Measured from the deepest ( center) of the ifp to the top of the shock body. I used a pencil, but any skinny tool should work.
    I think I mentioned above the shock end cap requires a 32 mil wrench. Bike shops have these, since they're used for threaded headsets.

    2.5 weight oil is kinda hard to find. I got some from a motorcycle shop. Any good suspension oil should be fine.

    This shock is not much different than your DHX. You're over qualified!
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  17. #17
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    Ive got 2.5 wt and the 32 mil headset spanner. The main difference with the dhx is obviously the piggback chamber with the ifp inside. The DHX is a PITA to be hones compared to the curnutt looking at it.

  18. #18
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    And thanks for taking the plunge and servicing the Curnutt and then posting it!

  19. #19
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    Quote Originally Posted by allmountain76 View Post
    And thanks for taking the plunge and servicing the Curnutt and then posting it!
    NP. Glad to see others doing it. Me and Katana (also in this thread) have rebuilt 2 Curnutt Coils and one Curnutt Air and each has worked out great.

    Only problem is not having info on which oil to use and what to do for IFP depth. We've had to rebuild each shock several times, figuring this stuff out. it's really simple though - and nice to be able to fine tune the ride.
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  20. #20
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    Oil volume wise, I guess no oil on the air side of the ifp. How much are you adding into the shock body side you recon?

  21. #21
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    Quote Originally Posted by allmountain76 View Post
    Oil volume wise, I guess no oil on the air side of the ifp. How much are you adding into the shock body side you recon?
    6 or 7 ounces, maybe? I set the IFP at 5.3" and fill the shock body about 3/4 full. Then plunge the damper and fill the rest of the way up.
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  22. #22
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    doe they normally run 2.5 weight? i'm coming in at 250lbs and want a little more small bump... would you recommend 5.3" for a fatty or run it a little shorter?

  23. #23
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    Quote Originally Posted by shmoodiver View Post
    doe they normally run 2.5 weight? i'm coming in at 250lbs and want a little more small bump... would you recommend 5.3" for a fatty or run it a little shorter?
    Updated, as I wrote up a little more detail.

    I didnt have any directions from Foes, so I had to figure out the IFP depth myself - and I took two tries to do it.

    The good news, is you shouldnt break anything if you're careful - so go for it. Here's all I did to find the starting IFP depth.

    rebuild your piston

    rebuild the shock body

    Either depress or remove the schraeder valve internals - the way the IFP can move freely in the shock body - without air pressure causing any affect.

    Insert the IFP into the shock body

    Use the piston to push the IFP all the way into the shock body. screw the cap onto the shock body - and push the IFP all the way to the point where the shock is at bottom out.

    If the bottom out bumper gets in the way, you will need to account for this later.

    Now with the schraeder valve still depressed, or removed - reverse the process, leaving the IFP at the bottom out point. Take the shock apart, again - removing all internals, except the IFP.

    Use a pencil or something else to measure the IFP depth.

    If the bottom out bumper prevented your shock from fully bottoming out - measure the width and push the IFP down further - by this amount.

    Now to make sure that during use your piston doesnt contact your IFP, you will want additional space between the IFP and the piston.

    I recomend starting at 1/2". Go ahead and push the IFP in, further by this amount.

    Re-install the schraeder valve core. you now want the ambient air pressure to hold the IFP at its current depth.

    Go ahead and refill your shock with oil - making sure to get rid of all bubbles as you go. (cycle the piston, etc)

    you should probably leave the coil spring off for now.

    Once back together and before charging the IFP, cycle the shock to make sure everything is moving nicely and you dont have interference.

    At these low pressures and forces, you shouldnt have to worry about any burps between air and oil chambers.

    To be 100% certain you have good clearance - you might want to bolt the shock onto you bike, no spring and completely cycle the shock - all the way to bottom out. Do this carefully and slowely - as you still dont have any significant pressure holding the IFP in place.

    When you're satisfied you have clearance - pressurize the IFP (minimum 50 PSI) and put everything back together.

    You'll notice in my thread that I took two tries to the the IFP depth I liked. Once you get the hang of this, you have much more flexibilty in fine tuning your shock - you can really dial in how it ramps up, which is nice.

    Disclaimer - I'm not a professional! I just have a bunch of Foes and decided to teach myself how to rebuild my shocks. This may or may not be the best way - but it works.
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  24. #24
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    Quote Originally Posted by iheartbicycles View Post
    6 or 7 ounces, maybe? I set the IFP at 5.3" and fill the shock body about 3/4 full. Then plunge the damper and fill the rest of the way up.
    I've been following this thread for a while, thanks a ton for the last update. I'm pretty sure I follow everything about setting the IFP depth 1/2" deeper than the piston could ever travel. One question, hopefully it's easy, what procedure do you use to fill the shock oil? Does the compression valving open easy enough to purge all of the air below the piston when pushing down? And what about getting all of the air out on top? I've seen some people put the entire shock under oil to get air out? Any insight? Again, thanks a ton!

  25. #25
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    Quote Originally Posted by erniek View Post
    I've been following this thread for a while, thanks a ton for the last update. I'm pretty sure I follow everything about setting the IFP depth 1/2" deeper than the piston could ever travel. One question, hopefully it's easy, what procedure do you use to fill the shock oil? Does the compression valving open easy enough to purge all of the air below the piston when pushing down? And what about getting all of the air out on top? I've seen some people put the entire shock under oil to get air out? Any insight? Again, thanks a ton!
    On the coil Curnutt this is very simple. The air bleeds out very easily and when you screw in the upper cap - it displaces some volume - and will spill out a bit. This gets rid of whatever air you might have on that side of the cartridge.

    The air curnutt is much more difficult as you have to do the above and screw the airsleeve on at the same time - so overspill ends up in the air sleeve. Then you have to bleed it out separately.
    Last edited by iheartbicycles; 02-22-2013 at 02:01 PM.
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