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Author Topic: CB-1 oem rear shock  (Read 2676 times)
a_morti
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« Reply #15 on: June 13, 2017, 05:28:27 AM »

Cbr900 shocks have all the adjustability you can want and are a little longer than cb-1 shocks. The springs are way too soft ofc, but looks like you have the tech to work it out.

http://www.customfighters.com/forums/showthread.php?t=12827
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ModerateFkr
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« Reply #16 on: June 13, 2017, 09:38:42 AM »

Cheers Jerry,

I'm hoping Nicknitrous had some luck with his Blackbird swap. Looks like we're heading towards amassing some serious data on the rear suspension of the CB-1. Although I'm not planning to make a race machine, and to be fair, in my youth I managed several pretty fast laps of Donington on my beautiful, though weave prone old CB250G5, I'm now a fair bit heavier, and out of practice on two wheels. So I need a safe ride as much as anything. But if I can really tune it to my weight and riding style, especially with a frankenshock I've built myself, I'll be delighted. Plus ill have something else to yak about when I visit Matlock Bath, Brighton and the Ace Cafe Wink)

I've got spring compressors that I bough recently to do the rear suspension on my Mondeo. What other special tools will I need to strip shocks?

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VintageHunter
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« Reply #17 on: June 13, 2017, 10:51:00 AM »

I keep reading this option as being a "no-brainer" but...I also read that this option doesn't allow the shock to be rebuilt?
Cbr900 shocks have all the adjustability you can want and are a little longer than cb-1 shocks. The springs are way too soft ofc, but looks like you have the tech to work it out.

http://www.customfighters.com/forums/showthread.php?t=12827
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Sugs
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« Reply #18 on: June 13, 2017, 09:35:18 PM »

I keep reading this option as being a "no-brainer" but...I also read that this option doesn't allow the shock to be rebuilt?

Pretty certain they can be rebuilt.  If you go to racetech.com and look for CBR900RR, it shows options for the rear shock, all years.  If it wasn't rebuildable there would be no options for the rear, like the Honda 919 for instance.
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VintageHunter
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« Reply #19 on: June 13, 2017, 09:54:48 PM »

Really? the Honda CBR900RR OEM rear shock "can" indeed be rebuilt?
huh. I wonder how much that'll set me back from RaceTech. I'll call them tomorrow and find out.
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Sugs
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« Reply #20 on: June 14, 2017, 12:57:28 AM »

1. You have to insert a nylon washer onto the shock shaft so you can collect shock displacement measurements.  To get the nylon washer on, you cut the washer and use a needle nose pliers to feed the washer through the spring and onto the shock shaft.  You might have to turn the washer sideways to slip it on the shaft.  You can get a washer for $1 at Lowes or Home Depot.  Make sure the ID of the nylon washer is snug enough to hug the shock shaft.  If you have to add some electrical tape around the washer to reduce the ID, that is okay. 
2. Put the bike on the centerstand
3. Dial out all the preload on the rear shock
4. Push the washer up to the shock body
5. Gently, let the bike off the centerstand, then put the bike on the centerstand again - do not get on the bike.  The weight of the bike will compress the shock and move the nylon washer.  Measure the distance the washer moved - try to be as accurate as possible, say within 1/16".  It is tight in there, but if you use a popsicle stick and pencil, you can mark the distance and measure the marks after you are out of the shock spring.  Then push the washer back up against the shock.  This distance I will call the bike sag.
6. Now you mount the bike and gently take the bike off the centerstand.  Balance yourself and lift your legs off the ground so your weight + the bikes is on the suspension.  Then, dismount and put the bike back on the centerstand.  Be careful not to bounce the bike.  With the bike on the centerstand, remeasure how far the washer moved.  This is what I will call rider sag.
7.  Go measure yourself as you were dressed so I have the exact rider weight for the rider sag test.

I can try to do this, but do you have a process to do it without a center stand as I don't have one on my bike?
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« Reply #21 on: June 14, 2017, 06:46:58 AM »

sugs,

If you do not have a centerstand, you can use your sidestand.  Skip the part where you do the bike sag.  You'll have to rely on the data from others for the bike sag measurement.  Try to get the rider sag measurement.

I will try to post my results this weekend.  I did some work yesterday and realize how tight the shock is buried in the bike.  You will have to remove the shock from the bike to get the nylon washer on.

ModerateFkr:  we're of the same mindset on the end result.

Jerry
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ModerateFkr
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« Reply #22 on: June 14, 2017, 08:14:36 AM »

sugs,

If you do not have a centerstand, you can use your sidestand.  Skip the part where you do the bike sag.  You'll have to rely on the data from others for the bike sag measurement.  Try to get the rider sag measurement.

I will try to post my results this weekend.  I did some work yesterday and realize how tight the shock is buried in the bike.  You will have to remove the shock from the bike to get the nylon washer on.

ModerateFkr:  we're of the same mindset on the end result.i

Jerry


Hi Jerry,

Rolling the back wheel of the bike off the edge of a step or lump of wood or a concrete block the height of a pavement/sidewalk edge could have the same effect as rolling off the centre stand I suppose.  But access to the unit is a bugger! Long nosed pliars? Not had chance to review the job yet.

It's a logical mindset, and a sensible place for all bikers to start. If you happen to end up with a safer part time racing snake too, well that's a bonus IMHO.

Good luck in the lab. I'm moving and replumbing electrical appliances and building storage spaces for the next few days.

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VintageHunter
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« Reply #23 on: June 14, 2017, 10:45:43 AM »

my CB1 doesn't have the center stand as well.
Let me see what I can do this weekend. if you got photos of the whole "nylon washer" process that would surely help.
1. You have to insert a nylon washer onto the shock shaft so you can collect shock displacement measurements.  To get the nylon washer on, you cut the washer and use a needle nose pliers to feed the washer through the spring and onto the shock shaft.  You might have to turn the washer sideways to slip it on the shaft.  You can get a washer for $1 at Lowes or Home Depot.  Make sure the ID of the nylon washer is snug enough to hug the shock shaft.  If you have to add some electrical tape around the washer to reduce the ID, that is okay. 
2. Put the bike on the centerstand
3. Dial out all the preload on the rear shock
4. Push the washer up to the shock body
5. Gently, let the bike off the centerstand, then put the bike on the centerstand again - do not get on the bike.  The weight of the bike will compress the shock and move the nylon washer.  Measure the distance the washer moved - try to be as accurate as possible, say within 1/16".  It is tight in there, but if you use a popsicle stick and pencil, you can mark the distance and measure the marks after you are out of the shock spring.  Then push the washer back up against the shock.  This distance I will call the bike sag.
6. Now you mount the bike and gently take the bike off the centerstand.  Balance yourself and lift your legs off the ground so your weight + the bikes is on the suspension.  Then, dismount and put the bike back on the centerstand.  Be careful not to bounce the bike.  With the bike on the centerstand, remeasure how far the washer moved.  This is what I will call rider sag.
7.  Go measure yourself as you were dressed so I have the exact rider weight for the rider sag test.

I can try to do this, but do you have a process to do it without a center stand as I don't have one on my bike?
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spacetiger
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« Reply #24 on: June 14, 2017, 06:59:57 PM »

I probably should have posted a few more details of the journey this is going to be.  Right now, it is a bit early to jump to shock options.  I know that is the natural thing we ask, but we have to lay some ground work.  Hopefully this post will help some.

We have to make sure we understand the oem suspension geometry before we go making changes, so we can make informed changes no matter what kind of end state we want to achieve.  That way its not guesswork on the end result.  You should be able to get the end state 1st time out of the gate.  So, we need to understand the rear suspension geometry.  It will take 2 posts to do this.  I can post half of it tonight and with any luck, can get the 2nd half done tonight for a posting this weekend.  Then with some sag and riding data, we can complete the rear data set to allow some changes.

So, first step is to understand the oem shock to swing arm geometry.  In pic 1 you can see a theoretical suspension where the shock compresses a distance and the suspension moves the same amount.  that relationship is depicted by the red diagonal line.   The doted line shows an example of the shock compressing 2" and the swing arm compressing 2".  This nice linear relationship isn't likely to be found in the real world because the lower shock mount has to be at the rear axle and be almost oriented vertically (90 degrees).  The closest bike I have ever seen to this is the Honda PC800.  That bike has ~vertical rear shocks.



So now I have to collect this information.  Because the access is so tight, i have to add a "crude" ruler to the shock so I can eyeball how much the shock has compressed - see pic 2.



Then, I install the shock and set up the bike with a jack under the swing arm.  Here, I can eyeball the shock compression distance, then measure the change in axle height.  Here is the test configuration.



Once you collect 5 data points, it is enough to curve fit the shock to swing arm relationship.  In this pic it is a nice curve fit.  I extrapolate the curve out to where the spec rear suspension is stated (110 mm) and the measured max shock compression potential.  That dot is the brighter blue dot at about 1.5" shock compression/4.3" swing arm compression.  You can see the curve fit at that point is very close to the stated oem rear suspension travel/shock measurements confirming I have a good curve.



Just to show another shock/swing arm relationship, in this curve I had done on my HD XL1200T (green curve).  Every bike is different, so you have to do this everytime you are going to make suspension changes so you know what the possible outcome is likely to be.



Now I can understand the oem set up integrating the spring info with the shock/swing arm relationship.  In this curve, it would show what standard suspension guidelines would yield.  The red/blue line shows what spring rate you are using based on the shock compression distance.  The standard guidelines is to set rider sag at about 25% of suspension travel.  You do this by adjusting the preload for rider weight.  Once you set this, you can see you have a max of 1.24" of shock compression to go which translates to about 3.25" more of suspension travel to go.  That is for solo or 2 up riding.  The problem with this is that the capacity of the shock (spring/damping) isn't up to more beefier riders or the more aggressive rider.  You can also see the where the rubber stopper begins; the total reported suspension travel means you smash the stopper to pieces if your suspension strategy is to use most or the entire shock stroke.  This leads to the question, how and what to change to best set up the suspension for you instead of using a setup for a wide range of riders armed only with general rules of thumb(?).



Math can help you figure out some options before you actually change things and is free.  To verify what is doable, safe and will make sure the center stand still works, we measure and check for options.  On the center stand, I see the oem setup leaves a distance of about 1.75" from tire bottom to ground.  If I am willing to live with 75% of that distance, then I want to look for an option of shock length that gives me (0.75 x 1.75") a 1.313" length.  I do a quick check of what is possible with the oem shock.  In this pic, I unwind the lower shock clevis until it is barely hanging on the shock shaft.  That max [unsafe] distance extension is ~11 mm.  It takes 5.5 full turns to screw on the clevis (5.5 x 360 degrees) = 1,980 degrees.  If I back off 20% so I stay in a safe extension, I find I can unwind ~400 degrees and yield a ~3 mm extension. edit:  the 2nd pic was the result of unwiding 2 full turns (720 degrees); that yielded over 5 mm of extension.  A nice gain, but perhaps not margin on the clevis to shock shaft overlap.



More math.  The equation of the curve fit can be used to show what happens if I lengthen the shock 3mm and 1.3".  I have integrated the max 4.3"/1.5" shock with the 5 data points to update the equation of the curve then project backwards.  Because of the oem geometry, i do not have to lengthen the shock very much to move the swing arm a much greater distance.  The small 3 mm (1.18") change moves the swing arm almost 0.5" (~0.47").  You only have to lengthen the shock by 0.32" to lower swing arm ~1.3".  So now, you know what length to make the Frankenstein shock (0.32" longer than stock).  Anything longer will put the rear tire on the ground.  BTW, the VTR1000 shock is 1.2" longer than the oem CB-1 shock - so it is too long.  If you use this shock, the rear wheel will not only be on the ground with the center stand, the spring will be compressed and make it easy to bump the bike off the center stand!  BTW, The CBR900 shock isn't long enough... I measured it already.



Assuming you can make the Frankenstein shock this long, you can start to plan the suspension strategy.  In this pic, it depicts a single rate spring on a longer shock with the same 1.5" max stroke.  You set the rider sag point at 20% and make it based on the shock stroke - not the suspension stroke.  The reason for this, the initial starting point has the best geometry for rake angle.  So you don't want to give away the best steering geometry just sitting on the bike.  You can also select the height of the rubber stopper so the nylon washer will always be able to tell you how much of the suspension you are using when you ride solo.  So knowing the range you want to stay in for good steering geometry, you can pick the spring rate and damper strategy for your solo riding weight.



So, you know more about the go forward plan.  I will measure suspension geometry (rake and trail) for different rear axle heights tonight (hopefully).  I'll try to finish that and post it this weekend.  After that, we need some empirical data on bike and rider sag + some riding data (to characterize the damping of the rear shock).  Once I get the shock dyno set up, we'll have better data - but, until then, we will only have what the riders can contribute via the nylon washer data.  I'll post this weekend how to do this.

Cheers,
Jerry  

Note:  a special thanks to all my teachers that helped me learn many things...
« Last Edit: June 16, 2017, 02:00:49 AM by spacetiger » Logged
VintageHunter
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« Reply #25 on: June 14, 2017, 07:46:12 PM »

one word........................."numb"
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spacetiger
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« Reply #26 on: June 14, 2017, 09:10:38 PM »

VH, numb nuts?  We're are not going to do this half ass you know.

Anyways, some pics to break up the math/graphs.

Pic 1.  comparing the CB-1 shock to VTR1000; 31mm which is too long



Pic 2.  CBR900 compared to the other 2.  About same length as CB-1, good, but we are after something longer, so the search continues.



Pic 3. The washer size to get, got this one from Home Depot.  You can see how I cut it.



Pic 4.  Using a needle nose pliers to slip the washer on the shaft; the washer on the shaft.  It is like using a zip tie on the fork.  It is snug enough to sty where it is pushed, so it tells you (using the calibrated curve) what the max load is through the spring when setting sag + it tells you the max Net load (spring force minus compression damping force) when you ride,  Note: it captures only the max reading for that ride.  That is why you have to reset it every time you want to collect data.



Pic 5.  I didn't get all the time I wanted, so I only got the bike in position to collect the rake and trail data (tomorrow).  I have some homemade tools to do this.  Will post the results sometime this weekend.



I'm throwing a lot at you guys.  Let me know if something isn't clear and I'll see if I can answer any questions.

Jerry
« Last Edit: June 16, 2017, 02:05:38 AM by spacetiger » Logged
ModerateFkr
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« Reply #27 on: June 15, 2017, 12:36:33 AM »

I'm an empiric learner by nature Jerry, so my teachers don't get any apples. But you explain well, and I'm getting most of your process, and the theory all makes sense. Establishing our starting point is very valuable indeed. Plotting what actually happens on this specific model is crucial. Your contribution to the cause will be equal to that of the tuning guys in Canada, and actually of a great deal more practical use to more owners. I need to print out and read over a few times. First read is via my iPhone. If I lived near you I'd happily pop over to help. Hope the rest of your week goes well buddy.

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« Reply #28 on: June 15, 2017, 02:56:03 AM »

You're blowing my mind woth the detail,  and I'll re read this a few times before it sinks in. Very interested to see your findings in the end.

Worth noting 92-95 cbr900 shocks are longer than earlier years but have the same top and bottom fitment - they changed the design of the main frame. Do you know what model year you have there?
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« Reply #29 on: June 15, 2017, 10:33:13 AM »

Spacetiger:
what is the distance on the stock CB-1 shock eyelet to eyelet?
I've ordered a CBR900rr shock (93-95) and I'd like to know if that one is longer than the CB-1 length.

thanks,
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