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Discussion Starter #1 (Edited)
Like a few us here,as an experienced rider,I bought the CBR (in March 2013)as lightweight fun "sportbike",not as a learner or commuter.

After a very short while I realized that I was not really happy with the fork or the shock.The fork was just way too soft for me(I'm only 140#) and under damped.Easily fixed with Racetech springs and ems.
The rear shock gave me a very jarring shot up my back and shook my kidneys when I hit certain bumps above 80kph.I really wanted some adjustment on the shock.

Then on May 1 is succeded in giving my self a compression fracture of my T8 vertabra while mountain biking.Basically I crushed the front of a vertabra between my shoulders to about 50% of its original height.I'm lucky,and VERY happy to be walking :DNeedless to say it has made my back a bit sensitive,so something had to be done for sure now.

After much internet searching and research I discovered a cheap alternative to a Penske,Ohlins or Racetech could be a 2008-2012 Yamaha R6 shock.The R6 shock has adjustment for high and low speed compression damping,rebound damping and of course preload.

The R6 shock is about 6mm. shorter and has about 7mm. more travel but it has the correct top and bottom mount(well sort of).




 

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Discussion Starter #2
The upper pin mounts were of different diameters(10 and 12mm.)but I just swapped the CBR one onto the R6 shock.



The lower mounts had different size holes.The CBR 8mm. and the R6 10mm.The bolt that goes though this hole also goes through a hardened sleeve that is also an inner bearing race for part of the suspension linkage.So the sleeve cannot be drilled out to accept a 10mm. bolt.So I sleeved the R6 shock holes down to 8mm.
 

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Discussion Starter #3 (Edited)
As you can see in the above pics the R6 spring is loose.I had a local bike shop remove the spring so that once I had the shock mounted I could move the suspension and wheel through its full travel to check for clearance and or interference.Do NOT attempt to remove any compressed spring without the correct tools.I paid $30 to have the spring removed one day and reinstalled on another..Seemed a bit dear to me but was happy to pay it.

My bike is equiped with ABS and that made the job a whole lot more challenging.The ABS modulator is hiding in that big plastic cover located between the the shock and the hugger fender.

Now the SCARY part.
I CANNOT recommend this because it involves grinding away some of the frame crossmember that the top of the shock attaches to.
Here is a pic of the untouched (other than the paintpen marks) crossmember.I unbolted the mounts for the ABS module and gently moved it back a bit.I left the brake lines attached for the whole retofit but really it would have made it much easier if I had just completely removed it for the grinding/fitting stage.I used a compact 90* air powered angle grinder with a tapered burr to do the grinding but it was very tight.



Here are some shots after it was ground away enough to clear the top of the shock and the piggyback resevoir.I later finished it off a little smoother and painted it to match the frame.







Once I got it so that the top of the shock just cleared the frame I installed a 3mm. shim(read,washer) between the top of the shock and the crossmember to gain back 3mm of the 6mm. difference in shock lengths ,this also gave me another 3mm. of frame clearance.

Now the ABS module hit the shock's rear side.I Removed the shock again(it was in and out dozens of times) and bolted the ABS module back up to it's original mounts and gently levered the whole assembly rearward probably 20mm. until it's plastic cover just touched the hugger when the rear wheel was almost at full upward(compressed) travel. Now I reinstalled the shock again,the shock just lightly rubs on the ABS plastic cover and the plastic cover just touches the hugger.I figured what's the worst that can happen?A squeek?
I got the spring reinstalled onto the shock and installed the shock for the last time.And reassembled the rest of the bike,which was thoroughly dismantled.

 

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Discussion Starter #5
The great guys at Racetech told me that for my weight the ideal spring rate for the rear would be 9.4kg/mm.
The R6 stock spring is 9.8kg/mm. pretty dang close.That is only one spring rate off or in imperial terms about 22lbs/in difference.
The ride height is virtually the same and the sag without me on it is very close with the preload set to full soft.
I just completed this a few days ago and have not had an assistant to measure rear rider sag yet but will post it.
I set the damping adjustments to where Yamaha recommends as the "standard" setting to start with. and took it for a test ride.
 

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so that spring rate should be good for someone up to about 200 lbs? I'm 180 lbs so that shock shouldn't be too far off for me.
 

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Discussion Starter #7 (Edited)
AWESOME is right JME!!!
As I stated earlier:I CANNOT RECOMMEND THIS MOD because of the mod required to the frame crossmember and I am SURE that I will get flamed from some of the nannies on this site BUT........

I REALLY LIKE IT!!!!

The ride AND handling improvement from the Racetech parts up front(I have 20w fork oil to replace the 15w(needs a little more rebound damping)) and the "upgraded" rear shock is FANTASTIC!
After a spirited ride on the winding country roads around here I realized that my back never once complained(remember I just broke it) and I found myself riding over bumps and broken pavement just for fun to see what it would soak up. :D

Front springs and emulators and oil ~$300
Used 2008-2012 Yamaha R6 rear shock $60
Shipping shock to Canada $50
Spring removal and reinstall $30
Labor........at least 10 hours,yes I took my time but I am an experienced auto mechanic.

It is also my hobby,so WELL worth it.
If anyone finds an easier fitting, equally good and equally inexpensive alternative please post it here.
To my knowledge this is the first documented "retrofit" of another OEM shock to a CBR250 yet.

REMEMBER: I cannot recommend altering the frame of any motorcycle

HAPPY RIDING :)
 

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Looks like you did your homework before you ever did anything to the bike nice job, its your frame do as you want with it :) thanks for the write up nicely done. Might look into this myself as I hate how stiff the ass is on this bike
 

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Discussion Starter #10
Measured rider sag today.
Me(140lbs)on it with preload set to full soft and 3/4 tank of fuel the rear sag is 32mm.Many would say that is optimal.I may go 1-2 notches up on preload(R6 has 9 notchess) just to try it.
 

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32mm is exactly what I have on front and back. I need to have my shock on 5 to get that sag though.
 

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Discussion Starter #13
When you say your weight is 140 lbs, is that your normal street clothes weight, or your suited-up weight?
140 out of the shower,add 15-16 pounds with full gear.
 

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Discussion Starter #15
This thing just keeps getting better!
This little bike with improved suspension and HH front pads is a HOOT to ride!
The steering at speed through the corners is so much more precise.The handling is much more comfortable and confidence inspiring.
 

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Discussion Starter #17
2 months on this system and no problems other than big smiles and a lack of chicken strips.
 

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My R6 shock just came in the mail, so I guess I'm doing this. Did you turn your own bushing for the lower mount? I can't find small quantities of metric tubing for sale anywhere on the internets.
 

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Discussion Starter #19
Yes,
I just made my own.
Let me know your thoughts when you're done.
 

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Aight, fin. That's one way to blow up a Sunday. I report to all that today I installed the 2008-13 R6 shock into my non-ABS, and NO FRAME MODIFICATION WAS NECESSARY!!

Instead, I spaced the shock down further so that the piggyback reservoir would clear the frame cross-member. The stock upper shock-mount nut is not long enough to accommodate the quantity of spacers required; the solution begins with dremeling out the welds that attach the bolt to the u-shaped bracket:



A cut-off disc makes short work of those welds, and the bolt pops right out. I replaced it with a 12x1.25 pitch, 50mm length. 50 was too long and I ended up having to cut it down; 40mm is the right length. For reference, my machine shop is my 360 square foot downtown apartment, and my work garage is the sidewalk out on the street. Suffice to say, I don't have a welder to tack the new bolt back in place. This is not of consequence, however, as the whole reason for the longer bolt is to add spacers. The solution is to add a 12mm locknut to the other side and let it be part of the spacer stack:



To this, I added two 12mm fender washers with total thickness of about 13mm. In the net, this makes the new shock about 8mm longer than the stocker.

I found the lower mount of my R6 shock to be narrower than the suspension linkage by nearly 2mm and consequently I had to file aluminum away from the both insides of the lower shock mount to make it fit. After filing about 1mm total from the shock, I discovered that it fit over all of the linkage except for the bearing itself. At this point I elected to pull my dremel out once more and remove the remaining 1mm of thickness from the bearing instead of from the shock. Stock, the bearing sticks out past the outermost lip of both bearing seals with room to spare, so there seems to be ample overhead to make the sacrifice. Modified, it still appears to engage both bearing seals completely, so I do not anticipate any accelerated bearing wear from this change.

I used 12mm OD nylon bushings for the reducer bushings on the lower shock mount. Fit into the shock was exact, but milling the ID to the bolt size was a nightmare with tools available to me (files, drill, dremel, yelling, 10mm tap, knives). On a second go, I would probably just do a couple wraps with a sliced-up beer can...

It works, and a helluva lot better than the stocker. I did a five mile shakedown this evening after bolting everything back together, tight twisties, and lots of traffic calming bumps at high speed. Just better all around. At 700 miles I installed racetech springs for my 195lb weight and cartridge emulators because it was soo obvious that the front needed to be fixed with the wallowing, imprecise steering in corners and excessive brake dive. The front remains the more important mod, but this is still another dramatic improvement. No more riding over some li'l bump and feeling the front eat it up only to have the rear go into hydraulic lock immediately afterward. Those same traffic calming speedbumps used to catapult the rear end up; tonight it arced gracefully over them. Ride height seems to be about the same, maybe a skosh higher but I couldn't detect any more quickness in the steering. All the damping controls are easily accessible. Getting a lockring spanner in to do the preload should be doable, but I'm not sure how. Probably need to remove the right footpeg / brake assembly and the rear reservoir.

$80 total, shock and all extra hardware. I just turned a little bit more into my mom (frugal) and my dad (mechanic).



 
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