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Help Honda CB125S USA spec - I need better fork springs.

Discussion in 'Honda 250cc Singles' started by grcamna5, Oct 3, 2021.

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  1. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    With fork that small in diameter you're well into the domain of fork springs that would be suitable and likely available in the huge Asian scooter market, and they've got some crazy racing hopup parts for their scooters, BUT they're also very lightweight [even though they stack up to 5 on the one bike] which means that spring rate you require wouldn't be available
     
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    ruckusman, Nov 7, 2021
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  2. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    I have had success with putting a car valve spring on top of the standard fork spring.
     
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    Murdo, Nov 7, 2021
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  3. Alan f.

    Alan f. US Spec CB250 Nighthawk 1993

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    That reminds me of my former 1981 CM400C that had two separate springs in each fork. I added 20mm spacers on top but never did add any air pressure (3-11psi was spec)

    [​IMG]
     
    Alan f., Nov 8, 2021
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  4. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    I got the idea when years ago I opened some Yamaha 100cc forks and one side had about 8 valve springs while the other had the normal spring. Always wondered what happened to the Yamaha spring that someone would fit the valve springs.
     
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    Murdo, Nov 8, 2021
    #24
  5. grcamna5

    grcamna5 Active Member

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    DannoXYZ,
    I haven't attempted to measure them yet.
    I called a person up in the PNW who's a dirt bike suspension expert and he said he would get a set custom made for me when I'm ready.I've had to spend what little I have on dental lately and I've postponed the front springs but will be doing that when I build-up a bit more $.
    I had sold motorcycle parts on Ebay for a number of years also but lately(since May 28,21')they have discontinued their policies with Paypal:in the past they deposited payments for sellers directly into Paypal,although now Ebay has switched over to something called 'Managed Payments'.. I will now need to open a separate checking account so the 'watchdogs' don't penalize me for deposits into my original checking account considering I'm on SS and receiving federal assistance for housing.
    The $ has always been a difficult issue.
    I do have many older Honda street bike parts to sell,lots of CB350 twin stuff,etc.
     
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    grcamna5, Nov 11, 2021
    #25
  6. grcamna5

    grcamna5 Active Member

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    I'm rebuilding an 83' Honda XL200R engine I have and installing an XR200R piston and camshaft;I'll be installing it shortly.The XL200R has the much more powerful OEM 12vt. stator and I'll look forward to running it all over,even in town where it won't discharge my battery while sitting in traffic idling.
    I'm going to open up my new checking account tomorrow and I'm looking for a better set of springs.I really do need to measure the spring rate of my original 81' CB125S springs.
     
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    grcamna5, Nov 12, 2021
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  7. grcamna5

    grcamna5 Active Member

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    Hello Danno,
    I found a place in Oklahoma City,OK. called Cannon Racecraft which sells springs of different sizes and makes custom springs for suspension and clutches.I sent one of my stock fork springs to them to measure spring rate and calculate what I would need for the correct custom springs on my little bike.The good news(what little there is) is that I have exact specs on my stock springs and the man who calculates the new custom spring rate for me has given me those numbers also.
    There was a problem with them sourcing the correct gauge wire for the custom springs.. :( and so now I have to be patient..
    They told me that that size/gauge wire won't be available here in the USA for about 5+ months :headbang:
    I am Very bummed-out by that news.
     
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    Last edited: Feb 27, 2022
    grcamna5, Feb 27, 2022
    #27
  8. DannoXYZ

    DannoXYZ Well-Known Member

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    Yes, good news! This is progress!
     
    DannoXYZ, Mar 9, 2022
    #28
  9. DannoXYZ

    DannoXYZ Well-Known Member

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    Now that you've got source for replacement springs, might as well modify existing ones. Nothing to loose. Aim for replacing 4-6" of coils with solid PVC spacer, +1/2" preload. Can actually calculate resultant spring-rate beforehand.

    1. chop off 4" of spring, replace with 4.5" of PVC pipe and give that try. If still too soft...

    2. chop off another 2" of spring. Use 6.5" spacer.

    Here I am replacing factory spacer on Ninja 250 forks with longer one after chopping stiffer spring (ordered not stiff enough).

    [​IMG]
     
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    Last edited: Mar 9, 2022
    DannoXYZ, Mar 9, 2022
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  10. grcamna5

    grcamna5 Active Member

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    Danno,that is an option.
    I'm looking online for a heavy duty 17.50+mm O.D. pair of aftermarket front fork springs for the Honda CG125 which uses the exact O.D. 27mm front forks as my bike:there are a LOT of Honda CG125's across the world(none here in the USA)and there just might be a pair of quality aftermarket front fork springs between .40-.50 kg. somewhere.The CG125 is a Very plentiful bike and there Must be a pair of heavy front fork springs around on the internet somewhere.
    I like these front forks,they're in great condition(I have a fresh set of NOS OEM Honda front fork tubes installed)and I won't abandon this excellent stock front-end because a couple USA custom spring builders tell me they can't get the size/gauge of spring wire(suppliers?)that I need:according to them it's not available now and this size is not common here.The stock springs I run now are 17.70mm O.D. and 457mm/18" long,which is small:non-USA is my only option,from what I can see. :neo:
     
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    grcamna5, Mar 11, 2022
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  11. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    The other option is to do what has been done on my SRX250 forks I just got... they were fitted with some heavy duty Valve Springs..... yep, and boy did that put come pressure on the cap when I undid it...lol
     
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    Andych, Mar 11, 2022
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  12. grcamna5

    grcamna5 Active Member

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    I understand,agreed.
    I imagine I could also use clutch springs as preload? My fork springs O.D. being 17.70mm may be similar to clutch springs.. I like this idea. :thumb_ups:

    On another note: to Danno
    The thing that one of the suspension specialists just mentioned to me today over the phone is, I need to keep track of installing too much preload,so as not to load the springs too much to cause spring 'coil wrap-up' which may eventually damage them.This one suspension man said that chopping quite a bit off of springs and using long spacers can cause that.
     
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    Last edited: Mar 11, 2022
    grcamna5, Mar 11, 2022
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  13. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    What about installing some air valves in the caps and using a bit of air pressure to help the springs?
     
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    Murdo, Mar 12, 2022
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  14. DannoXYZ

    DannoXYZ Well-Known Member

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    Don't stack multiple springs, their combined rate will be less than either spring alone. That's because applying load will compress TWO springs instead of one. So instead of 1 spring compressing 1/4", you'll have 2 springs compressing 1/4" each for total 1/2". Much, much softer. https://www.acxesspring.com/calculate-rate-of-springs-in-parallel-in-series.html

    The effect from stuffing extra valve/clutch-spring is increasing preload, but not actually adding spring-rate. They will compress fully early-on, so acts as solid-spacer anyway. So you'll have more ride-height initially for higher suspension-travel, but under same load, that fork will actually compress more because combined spring-rate is lower.

    That's why you want to replace squishy section of original spring with something solid, like PVC. And too much preload is exactly that's why you only want 0.5". Up to 0.75". Without screw-type preload-adjusters, it's difficult to squeeze in more than that.

    Coil-bind is completely different aspect and has little to do with preload (which contributes small effect to coil-bind). It's how many free-coils and space you have between them. Typically, depending upon how the coils are spaced, you can chop spring in half to double spring-rate and it'll be OK. I've done that to forks on my '02 Ninja 250 since they're so soft. The '09 Ninja 250 springs I posted above are much stiffer and required much less chopping. Post picture of your spring and let's measure how much space you have in between coils vs. wire-diameter itself. Typically the softer springs have more space between coils.
     
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    Last edited: Mar 12, 2022
    DannoXYZ, Mar 12, 2022
    #34
  15. grcamna5

    grcamna5 Active Member

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    This is my stock(17.70mm O.D. x 18"/457mm Long)OEM spring.There are 6mm between coils at the widest and the wire diameter is 2.95mm.

    I shortened a pair of 33mm O.D. springs before and used a chop saw with it's own vise to hold the spring tight.I noticed the finished cut wasn't as stable looking as the original end of the spring was.. I wasn't convinced that the cut end had enough flat surface to completely support it?
    20220312_135540.jpg
     
    Last edited: Mar 13, 2022
    grcamna5, Mar 13, 2022
    #35
  16. grcamna5

    grcamna5 Active Member

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    I weigh 225 lbs. now and might carry a lightweight passenger very rarely.
    I would like to be able to load the bike up to the 325lb rated carrying capacity without worrying my front springs will bottom all the time.
     
    grcamna5, Mar 13, 2022
    #36
  17. DannoXYZ

    DannoXYZ Well-Known Member

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    Ok, so you've got a 2:1 ratio of space to wire ratio on spring to compress. That means 18" spring can compress down to 6" to reach coil-bind, giving you 12" of suspension travel! You're only using 4-5" of travel before damping-rod bottoms out. So there's 8" of chopping we can do to increase spring-rate. Start with chopping 6" and installing 6.5" PVC spacer. With progressive spring, chop end with closer-spaced coils.

    Here's how it's comes from factory on newgen Ninja 250. It has 4" steel spacer on top of spring, probably last minute design change to deal with heavier foreign riders.

    Note this is NOT increasing preload by +4", spring is shortened 1st, then that missing section is replaced by solid spacer. Preload ends up being same, top of spacer sticks out top of fork-tube by about 10mm, same as original spring.

    [​IMG]
    Note steel washer between spacer and spring. Not uncommon to chop additional 4-6" off factory spring an replace spacer with 8-10" PVC to increase spring-rate for heavier riders or track use.

    I used to heat up last 1/2 coil on spring to deep cherry-red and push down on floor to make end square. I found that was not necessary when using steel washer between spring and spacer. Or install spring with cut end facing down.

    In '80s, when no aftermarket performance springs were available, all that was available to improve spring-rate for track use was to chop springs and replace with solid spacer. Not uncommon to chop 6-8" off springs. I still have VF500F that I did that with in '86.

    [​IMG]

    Other things you'll want to do is use thicker fork-oil to match stiffer spring-rate. And raise oil-level 10-20mm to reduce air-pocket at top. This acts as air-spring and reducing its volume increases its compression-ratio to add more load-carrying capacity to fork.
     
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    Last edited: Mar 13, 2022
    DannoXYZ, Mar 13, 2022
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  18. grcamna5

    grcamna5 Active Member

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    Danno,I see what you mean on how to cut the springs with the illustrations(they help)and info.
    How do I calculate what spring-rate I arrive at and how much do I cut to arrive there?

    I like your 86' VF500F2 ! I had one just like it and miss that bike Very much.
     
    grcamna5, Mar 14, 2022
    #38
  19. DannoXYZ

    DannoXYZ Well-Known Member

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    Final spring rate is ratio of lengths.

    R0 = initial spring-rate
    L0 = initial length
    Lf = final length
    Rf = final spring-rate

    Rf = R0(L0/Lf)

    For example, you have 18" spring with 100-lb/in and chop in half:

    Rf = R0(L0/Lf) = 100(18/9) = 200-lb/in


    Or chop off 6" of same spring:

    Rf = R0(L0/Lf) = 100(18/12)= 150-lb/in


    Or if you want 130-lb/in rate:

    130 = 100(18/Lf)
    Lf = 100(18)/130 = 13.8
    18-13.8 = 4.2 to chop off
     
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    Last edited: Mar 14, 2022
    DannoXYZ, Mar 14, 2022
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  20. grcamna5

    grcamna5 Active Member

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    The measured progressive rate on my stock springs are: .28-.34kg.
    I would like to change it to .45-.52kg. This is the progressive rate that I desire:between those two numbers. thanks,Bill
     
    Last edited: Mar 14, 2022
    grcamna5, Mar 14, 2022
    #40
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