Topic: CB650 forks. All years, all lengths.

[Frankenkit]

I've got no rush on this, but when I finally get all my crap together to do this project, I only want to do it once.

I put 11.40" shocks on the rear of my bike, and they're great.  The problem is now the front, which feels really spongy and squishy when I hit the brakes.  This winter sometime, I'm plotting to lower my forks.  If I need to, I'll do Cyclex -1 or -2 tubes (I think the 650 tubes are 1/2" shorter than 750, but I'm not sure on that) with progressive springs. 

However, reading over old posts/threads, there was some discussion about the 1981 CB650 Std. having tubes that looked almost 2" shorter than the custom.  I'm not sure how that worked for their geometry, but I'm now contemplating getting a set of those off Feebay or somewhere and still putting in progressive springs that fit that length.  The only caveat is that the progressive springs available for the 1981 CB650 Std are noted by Progressive to be "slightly short for the tubes, leading to slow turning, etc"  ... and I don't want to go TOO short, so as to adversely affect handling. 

I'm open to suggestions, but I'd like to keep the angles as close to what was originally intended stock for handling/braking purposes. 

This was from CBJoe:

with an '81 650c on the left, '81 650Std middle, '80 650c on the right.

Wondering also if the '80 650 standard is the same length as the '81 650std... that way I wouldn't have to mess with the air assist knobbies, either.

[Soos]

I have a set of '79cb650 sliders you can have for shipping if interested.

I'll measure them tomorrow.



l8r

[Hush]

I know you want to go to shorter forks/springs Kit, but that "spongy squishy" feeling is probably fork seals that need replacement and oil that should be renewed.
Cost me about $60 kiwi to redo mine.........have fun.

[Frankenkit]

Mate, I have brand new fork seals, dust boots and oil in my forks, but nice try. 

[cb650]

Instead of listing all the diff models you could break it into standard and leading axles. (single disk v dual)
The leading axles forks are longer but mostly below the axle mount. 
My standard measures 32.  I'll measure a leading axle latter.
Also what weight oil did you use in your front?  I use a little heavier 15 I think. 
But it is still a little soft to my liking.  Might try the shim thing next oil change.

[Frankenkit]

Ahh interesting thought.  I used 10w, thinking that'd be enough for my 115#. 
I'm going to stick with single disk front braking to keep things simple and stock-looking.

[gilesclement]

I've got severely squishy forks as well and would be interested in hearing about the shim idea. I'm using 15wt oil and redid my seals. Is there some sort of way of determining whether springs are fatigued? At the moment if i smack the brakes the front forks compress till there's only about 2" of inner fork protruding. Quite skitchy around corners.

[Frankenkit]

I'm writing on my thread, but I'll add it here,too.  I wrote Progressive Suspension about getting fork springs an inch or two shorter to lower my bike.   They sent me a .pdf and basically said 'good luck'.  The PDF is their spring spec sheet and I'll attach it here, but the take-home message (and one worth discussing here, I think) is that we may have some options at different heights.

the fork kit part number for the 1980 cb650c is 11-1108.  Those are 20.75" fork springs,  with a 25mm external diameter and 35/50 rate.

The kit part number that I'd look at to lower my fork an inch is 11-1120, which is a 19.75" spring, with a 23" external diameter and 35/50 rate.  That kit uses a 2.12 spacer, and I'm not sure what that 2.12 signifies, because some of their kits have 12.00 spacers, and I have a hard time believing someone would just put a foot of PVC in their fork.

The kit part no. I'd look at to lower my fork two inches (thereby making up the 1.6" for my 11.4" shocks and lost half inch to putting on a 16" tire from the 17 that's on there) is 11-1120S, which is 18.75 inches long, same 23mm OD and same 35/50 rate.  Shim is n/a in that kit. 

Well, maybe I need to think about the 2" drop in front, because if it started out stock in front, then they put on a 17" rear wheel, the front was -.5" (relative to the rear) Then I dropped the rear 1.6".  that 1.6 negated the .5" of the 17" rear wheel, making the rear 1.1" shorter than the front.

...

so I'm planning on putting the 16" back on this winter, which would raise the relative height difference to 1.6" again.  So I should probably go with lowering the front 1" and think about whether or not to lower the fork through the tripletree for that last half inch.

this is making my head hurt

[gilesclement]

yea, my head hurts now too.

I'm not really looking to lower my front as much as I am trying to get it stiffer. the PO of my bike was (quite conservatively speaking) a huge hulking lardass and I believe he just crushed the springs. I'm no state farm judge but I'd guess he tipped scales at 350lbs.

I'm not terribly thrilled with the idea of shelling out another 100 for springs on my beater though.

Anyone know if it's possible I just have too little oil in there? I filled it to the manuals specs but might have misunderstood something? Is there any way of checking?

[Frankenkit]

progressive springs are available all over the place for $65 instead of $100

[gilesclement]

yarhar!~ just found a set for 65 on evilbay.

anyone know how much of a project it is to replace them?

[Frankenkit]

Unless you're lowering them and have to f*ckdiddle with spacers, I THINK (you know someone will correct me) but I THINK you just:
* put the bike up on the c-stand, then jack up the front to unweight the front wheel,
* remove your handlebars (no need to take all the stuff off them, just the fuse box and move them out of the handlebar clamp for now)
*Carefully unscrew those caps- now mind you, they will be under a little spring pressure... don't get popped in the face or anything.
*take the old ones out, put the new ones in.


That's if you have all new oil and seals etc etc in it.
If not, you should probably go ahead and rebuild your forks with new oil etc too.  The fork oil in these monsters gets pretty foul. Mine looked like muddy coffee.

[gilesclement]

I'm really not sure that the tops of my forks come off. They're the air assist ones... I've had them apart to replace the seals once already and didn't see a spring floating around, it was buried inside the inner fork doo-dad thingy. The only thing Clymer says about it is take it to a dealer.