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Help ZXR250 fork tubes with different cap threads

Discussion in 'Kawasaki 250cc In-line 4's' started by XCite Bikes, Dec 28, 2022.

  1. XCite Bikes

    XCite Bikes Parts and Accessories Staff Member 250cc Vendor Contributing Member

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    Hello everyone. I need some help from ZXR250 owners. I've got now in stock 2 different types of fork tubes. The manufacturer lists them both as compatible with the same year range, but the thread for the fork cap are different: one has a 1.5mm, and the other 1.25mm.

    Would anyone here know anything about the difference? Is there a different year range for each one, or a different model (A & C)?

    I know Honda made a big mess with the NC30. They changed the fork tubes at certain point, and the only way to find out the difference is the colour of the adjuster on the cap. Hopefully with the ZXR250 it will be something easier.

    Cheers
    Omar
     
    XCite Bikes, Dec 28, 2022
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  2. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Hi Omar,

    I've got a set apart at the moment, I can measure the cap threads.
    I have measured the springs themselves and they are 0.6mm/kg; and
    One leg has the compression damping adjuster if that means it's a C model as I have a vague recollection that the A model didn't have compression damping adjustment.

    Both caps have rebound damping adjustment.

    Stay tuned for the thread measurement...

    EDIT - OK, the fork caps/tubes I have are 1.0mm pitch thread - measured twice with an actual thread gauge.
     
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    Last edited: Dec 28, 2022
    ruckusman, Dec 28, 2022
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  3. XCite Bikes

    XCite Bikes Parts and Accessories Staff Member 250cc Vendor Contributing Member

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    Thanks mate. Any chance the pitch would be 1.25? Was it a model C? Which year model was it?
     
    XCite Bikes, Dec 28, 2022
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  4. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Hi Omar,

    They're from this bike - https://www.2fiftycc.com/index.php?threads/wrecking-zxr250.8778/

    Said to be a 1992 C model, I think that's fairly definite

    I did try the 1.25mm thread gauge first, no go, so it seems that something is amiss somewhere.

    I'll take a pic of the thread gauge on the fork cap threads.

    Anything else that can assist pics wise?

    ...and I've just realised the potential mixup - I've been checking the thread on the fork caps, NOT the threads on the lower fork tubes.

    But fortunately I did just remove the lower fork lugs yesterday, so I will measure the thread on the lower fork lugs/chrome stanchion lowers, unless you're talking about the alloy fork uppers that you now have in stock...
     
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    ruckusman, Dec 29, 2022
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  5. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    OK, so I've measured the thread on the lower fork lug which screws onto the chrome fork stanchion, what I think you were referring to as the cap and the thread is 1.25mm, verified with a thread gauge.
     
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    ruckusman, Dec 29, 2022
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  6. XCite Bikes

    XCite Bikes Parts and Accessories Staff Member 250cc Vendor Contributing Member

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    Thanks mate, that's a great help. I know the 1.25 works on the 92 C model. Now I need to find out what other models use the 1.25 and what model (if any) uses the 1.5. Hopefully someone else that has a C or A model could help to add some info. Cheers!
     
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    XCite Bikes, Dec 29, 2022
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  7. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    Hi Omar,

    I don't have a tool for measuring thread pitch (is that what it's called?).

    I am assuming you're after the thread for these forks? ZXR250A on the left and ZXR250C on the right?

    A&C Forks.JPG

    I did have a ZXR250A apart of few years back and I have the following pic which I hope helps. If not, please let me know what part you're after and I will try to help. I don't have a vice or triple tree to use to pull the tops off these shocks at the moment. Sorry.

    Fork ZXR250A.JPG
     
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    Frankster, Dec 30, 2022
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  8. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Omar was after the thread pitch for the lower lugs where they attach to the chrome stanchions - your shots are extremely useful to tell the difference between the A model and C model forks by the upper fork caps.

    My C model upper fork caps are the same as yours @Frankster
     
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    ruckusman, Dec 31, 2022
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  9. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    The odd thing with that pic is that both of those upper fork caps are on ZXR250A forks. It would be good to know the exact timeline/configuration of the ZXR250 forks and their 'bits' and if there are any aftermarket caps that offer more modern tuning features or better performance. Might be a good thread option. I will post a pic of those forks (bottoms) later today.
     
    Frankster, Dec 31, 2022
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  10. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    OK, that's interesting, my caps has the central preload adjuster with the indicator lines like the right on in your shot

    I'll post a thread on removing the lower fork lugs, it was actually far easier than I anticipated and didn't require any special single use tools - there's lots of expensive 'solutions' out there which aren't necessary IMO.

    Idea is to potentially put different lower fork lugs for decent brake caliper options without messing around with adapter plates.
     
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  11. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    These are the two sets of forks that I mentioned previously. The ones on the left will only fit a ZXR250C front axle and the ones on the right will only fit a ZXR250A front axle. I guess the upper caps are interchangeable? The ZXR250C must have a lower front end?

    upload_2023-1-2_11-47-56.png [
     
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    Frankster, Jan 2, 2023
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  12. XCite Bikes

    XCite Bikes Parts and Accessories Staff Member 250cc Vendor Contributing Member

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    Apologies, I messed up on my original question. As @ruckusman pointed out, I need the thread pitch of the end of the tube, not for the cap. I got a picture yesterday, but I need to go back and take a picture with a thread gauge showing the exact measurement of each one.
    zxr250forks_02.png
     
    XCite Bikes, Jan 3, 2023
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  13. H05TYL

    H05TYL Active Member

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    The later A's (with the C style swingarm) have the C style fork caps in every picture I've seen of them.
     
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    H05TYL, Feb 1, 2023
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  14. XCite Bikes

    XCite Bikes Parts and Accessories Staff Member 250cc Vendor Contributing Member

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    Thanks. I created a confusion at the start of this post when I said "fork caps". The different threads I have on the 2 models are on the bottom of the tubes, not on the top where the caps go. Apologies.
     
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  15. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    That makes sense. I often wondered how or why some A models had C swingarms (I assumed they had been fitted after the originals were damaged); I never looked at the fork caps before this thread. So the caps are interchangeable between the different forks; that's good to know. I wonder how much of the Balius frame and suspension can be transferred to a ZXR? I'd like to put a Balius front end on a ZXR and maybe even check if the rear swingarm is also transferrable.

    L_balius_1996.jpg
     
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    Frankster, Feb 2, 2023
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