Zx6R shock + adaptor plate

[Extent]

Well I've finally gotten a bit of test riding in with the new shock and spring.  This bike is the only on I've ever really ridden, so I don't have much to compare to.  I still need to do some serious switching back and forth and making notes and planing a real test course to get the fine tuning down, but overall so far I'm pretty pleased.  The bike defenatly seems to wallow less after quick direction changes, I also think that it rides a little smoother over almost good pavement.

I tried to calculate the spring rate of the V spring, but came up with only 160 lbs, which seems exceedingly low.  I also have no way of putting enough pressure to bind the low rate coils, so I really can't measure the high rate portion of the spring at all.  The spring for the V is about an inch longer than the 636 spring, and it would have to be compressed almost that much just to fit on the 636 shock, even with an absolute minimum of preload setting.  I just decided to use the 636 spring and shock as a unit.

Now on with the fun stuff.

The shock needs to be slightly modified to fit in the V.  Namely it will need to be mounted upside down and the bottom eye needs to be drilled out slightly to fit the V mount pin (all directions are assuming the mounted direction)

The top of the shock is too wide to fit into the stock point ont he frame, so I made a plate to mount in the stock location that just has another hole drilled for the 636 bolt.  Both parts use the stock bolts from their respective bikes.

Here is the new shock with the spring compressors on, you can see the adaptor plate I cut up at the top.


To keep parts from sliding around I got sections of steel pipe just larger than the bolts they fit around and cut them as spacers so that the shock bottom and the mount plate bottom can't move around and stay centered.  I didn't cut spacers for the shock top bolt because it really isn't going anywhere.  I may do it eventually for consistancies sake, but for now it's the only bolt without spacers.

Here is a side view of the shock top in place with the adaptor plate.


and here is a top view of that.

you can see the spacers behind the first bolt.

Here's what the whole thing looks installed


Note that I used the collar from the Vision shock when I installed it instead of the 636 collar (you can see it in the spring compressor pic)  The 636 collar is a lot thicker and by using the V collar I don't even have to use the spring compressors to get the spring on, just loosen the preload all the way and pry them in with a screwdriver.  I also used the plastic shield from the V shock because it had slits in the side.  I slid the bump stop down all the way to the bottom of the piston so I could use it to judge how much travel I was using, basically the same thing as the ziptie trick on front forks.  Next time I have it apart again I'm putting the 636 dust guard back because it's solid.

You need to cut the undertail mudguard to fit around the resovoir, but that's simple enough to do.  I'm contemplating replacing the whole undertail and making a rear tire hugger myself.

With this shock the rear wheel has about a half inch or so more travel that with the 82 shock, and with the way the plate I have is now most of that hangs lower.  When the bike is on the center stand the wheel is just barely off the ground (but still spins completely freely)  I could raise it a bit more by drilling out a new adaptor plate, and I may still do that at some point, there just isn't very much room to push the shock forward without hitting the airbox.

When I had both shocks apart without springs I put them in and measured the exact amount of wheel travel each one allowed, and calculated what a rough 33% sag height would be.  Obviously the sag for the 636 would be higher than the original 82s, so I set my preload to fall just about half way between the two ride heights, which will be a lot closer to the 35% max sag often recomended for street riding but will keep the rear ride height as close to "stock" as possible (considering that the ride height changes with preload I wasn't too worried about geting that nailed perfect)

For shock settings I put the compression damping all the way soft (it's possibly a stiffer spring) and tuned the rebound damping so the rear completely recovers from a bump (me sitting down hard on the bike) in about 1 second, which ended up being something like 3 turns from soft.  That is much better than the original shock which springs all the way back up in less than a second.

The only other thing to note is that with this all mounted up you cannot make adjustments to the rebound damping setting because it is hidden underneath the gas tank, but you only have to undo the tank mounting bolt at the back and tip it up a little to reach the screw.  No need to pull the fuel lines and remove the whole thing.

[EH]

Not being a computer wiz I need some help. I cannot view any pictures that accompany some postings. All I see is a white box with a red x. Any help would be appreciated. Thanks

[MotorPlow]

All I get is broken links too.  Something didn't work.

[Wayne]

Same here. Nice looking red X's

[gbranche]

They worked for me. For reference, here are the links for the pictures:

http://levanthia.com/forum/download.php?id=44
http://levanthia.com/forum/download.php?id=43
http://levanthia.com/forum/download.php?id=42
http://levanthia.com/forum/download.php?id=45

Which browser are you using that doesn't display the pictures properly? Have you tried a different browser (such as Firefox)?

Greg

[Extent]

Sorry, they're fixed now because I fixed them.  I had the forum set to dissalow guest downloads.

If anyone can't see them it's probably because the browser isn't reading the headers right, since the preprocessor is just returning jpeg format data.  no reletively modern browser should have a problem with it tho I think...

[EH]

Thanks for the info! I am using Firefox but my computer is windows 98 from 1998.

[Glyn Pickering]

Nice work with the shock.

I'm going to do a similar project with a Triumph T600 shock I found on our local E Bay. The lenth seems perfect but the sping shorter with fewer turns. It has full damping adjustments like your shock. What would be a good starting point for tuning once fitted? Everything on "mid setting" and work from there?

I'd appreciate some advice as I do along since  suspension is a foreign world to me. I'm on pickteam@xtra.co.nz, would be good to get in totch.  

Regards

Glyn

[Extent]

Heh, well don't get the idea that I know what I'm doing  :P I'm pretty new to the scene, I just figure things out as I go along.  

As far as settings I don't think just mid settings is a good starting point.  You've got 3 factors in your suspention settings, the spring rate, compression damping, and rebound damping.  Both the spring rate and the compression damping work in the same direction, if you've got to crank up the compression damping your spring rate is probably much to low, and you should probably go to a higher rate.  You want to use as little compression damping as possible, because the higher you set the damping the harder you make the oil work, and as it heats up it looses viscosity and stops working as well which will hurt your ride quality a lot.

Rebound damping is what fights against the spring pushing your shock out to full extension.  If this is set too light then the spring will snap back quickly, causing a pogo effect.  If it's set too hard then the shock won't have enough time to return to full extension between bumps and you get a packing effect, where the suspention packs down to it's lowest travel and starts riding on the bump stop, effectively giving you a solid rear and causing an extremely harsh ride.  For setting this with the bike still push down on the tail of the bike hard and let go.  It should take about 1 second to return to it's static ride height.  Stiffen rebound to make it return slower, and soften it to make it rebound quicker.  If you find the rear packing while riding you need to soften it.

Compression damping is usually 1/5th as stiff as rebound damping.

Unfortunatly there is no way to really know how a shock is valved, so the adjustment ranges are very different from shock to shock.  You may not be able to get one or more of the settings dialed out far enough to be right for the bike, at that point you can have the shock revalved by a shop (if the shock is rebuildable) or you can get a different shock.

So short answer is compression all soft and dial up from there to taste (ride test it) and rebound start soft and adjust stiffer till the rear rebounds in 1 second.

[Glyn Pickering]

Nice explanation Extent. Gives me a good basis of tuning.

Be really interested to read of further tuning and results on your shock. Does it matter if they run upside down? I guess if they are sealed it shouldn't matter?

Will send some pics/ results of my shock job as it progresses.

Regards

Glyn

[Extent]

AFAIK nitrogen shocks can run in any orientation.  The nitrogen keeps the oil where it should be.  Damper rod style shocks (like our front forks) can not be mounted upside down.  If possible when you mount your shock put the piston side (the lighter end) down, so that that is the unsprung side of the shock.

[Extent]

Had it all apart to trim the fender and get everything installed again so I got a picture of the plate by it'sself



And also drew up a diagram with measurements

[jasonm.]

Note: the shock could binde if you do not have more steel or some spacers to stablize the steel adapter. Eventually the aluminum ZX shock ears could break off.

[ProfessorRex]

If you are running this shock upside down, the rebound and compression are flipped.  Because most shocks are valved with much higher rebound dampening than compression, when the shock is flipped, even with the minimal adjustments that can be made externaly maxed out, compression will be overdamped, and rebound underdamped.  I ran into this problem on my jeep when I changed my shock mounts and used upside-down front shocks on the rear (i've since changed it).

Of course this only applies to gas charged shocks, bilstein..etc... with diferent rebound and compression dampening rates.  The shock won't leak, but the shock will "think" compression is rebound, and rebound is compression.

If you need an experts oppinion from a verified sorce, bilstein customer service will tell you all about it: 1-858-386-5900 (that's the west coast number)

Or try an other performance shock manufactuer, they'll all tell you the same thing.

-Rex

[Extent]

Note: the shock could binde if you do not have more steel or some spacers to stablize the steel adapter. Eventually the aluminum ZX shock ears could break off.

Noted, I can easily just cut more spacers for that last bolt.

When I adjusted the rebound damping it was defenatly adjusted by the "correct" adjuster, even tho it was upside down.  Maybe because it is at an angle and not practically vertical like it is normally mounted.  I'll have to run thru it again and see if the other adjuster effects it as well.  Unfortunatly I've got more critical things on the bike to fix now  :-/

[ProfessorRex]

I'm sure that you were adjusting the shock properly.  What I'm saying is that mounting a shock upside down makes the valving improper.  This is only true on gas charged shocks... and truthfully, I'm not entirely sure why, sufice it to say when I made custom shock mounts for my jeep, I mounted front shocks that were lying around upside down, and the rates were WAY off!  and it was WAY noticeable!  I'm not an engineer, and the way it has been explained to me is that when a shock is upside down, the shocks acts as if the road is the vehicle, and the vehicle the tires.  Hence the rebound dampening is too light.  Maybe motorcycle shocks are different, but I doubt it.


EDIT:::
I just re-read your above post, I forgot it's almost flat.  I bet the difference in angle is slight enough that it almost doesn't matter, and the shock must be valved accordingly.  I was pulling from what I know - rock crawling jeeps - motorcycles are new to me.

[Extent]

What I meant was when the shock is in the correct orientation the bottom adjuster adjusts the rebound, with the shock inverted the same adjuster (now at the top) moving the trim needle in the rebound stack still seems to adjust the rebound, the valving hasn't reversed (or seems not to have at least)

In doing a little more research on it I've seen everything from "orientation dosn't matter" to "never mount upside down" to "chech with the manufacturer".  I can't quite wrap my head around the idea, since the shock isn't moving up and down, but in and out, wich is the same direction regardless of what direction it's facing (at least for gas charged and remote resovoir shocks)  The shock diagram I have dosen't help either.  I'll have to call around like you suggest and see if I can find if there's a differece between these types of shocks.

[ProfessorRex]

Yeah, I have trouble wraping my head around the idea... I know when I called Bilstein customer service explained it well.

[Glyn Pickering]

Just to put in my 10c wirth.

Saw a Honda V twin today. Do't know the model, one of those big Ducati wannabees. Thw rear shock was upside down, with the adjuster at the top and only the eye at the bottom. It wasn't an aftermarket shock but looked standard.

Be good to get a firm conclusion on this since I want to mount a T600 shock on my vee soon. Less unsprung weight makes alot of sense, so I'm going for the upside down orientation.

Regards

Glyn

[Extent]

Most shocks today are inverted already, but they were manufactured that way.  I'm talking about taking an "inverted" shock and turning it upside down again, so that the eyelet is at the top now, just like in my pictures.  I've got the heavey side of the shock unsprung, but just because there is no room for the resovoir under the tank.