Topic: Fork Spring Length (unsprung)? CB550 vs CB500?

[alacrity]

Factory part numbers are different, but the forks seem otherwise identical.  What am I missing here?  Progressive doesn't make a spring for the cb500k0-2, and their cb550 spring is a LOT longer than the stock (40 year old and sagged by how much??) spring I pulled out of the cb500 front end.

I can't find factory OEM fork spring lengths/specs posted anywhere.  If anyone has this info, it would answer the question pretty quickly for me.  Thanks!

Honda Part numbers are as follows:
cb500 1972 -51401-323-010

1974 cb550  51401-374-003

[dave500]

the lengths are in the workshop manual you can download here somewhere,it states the 500 as being 451.7mm(17.78") and allowable to 425mm(16.73"),the 550 is listed as the same ,im guessing thats the first 550s though?you can get your springs reset at any decent spring works,theyll heat them up and stretch them for you.

[alacrity]

Dave:
thanks for the response.  That's what I thought... and then these "correct" springs arrived from Progressive and it seemed impossible there could be a 4" difference in unsprung length.

[Deltarider]

When I had my springs out years ago they varied in length? Is that bad?

[Untold]

I just rebuilt my forks on my '76 CB550 and used Progressives. 
Filled with 165cc of 15w fork oil.
 I haven't taken the bike off the center stand yet (kickstand is off and it's in a weird spot so I don't want to have to fight to get it back on the stand), but I did rock the bike forward and try to push down on the forks. 
They won't budge. With the stock springs it was pretty easy to compress them in this position.
 Granted, I don't have the best leverage on the center stand, but I'm 6'5" 215lbs,

Are Progressives really that much stiffer?  They were definitely longer than the stock fork springs, but I didn't measure the difference.  Wondering if I used the wrong ones

[toytuff]

That's pretty heavy oil for progressive springs. I went with the progressive springs on my CBX and was told to run 7 to 10 weight. No more.

Went with 7 weight. Perfect!

tt

[Untold]

Cool, thought that might be a little heavy. I'll go lighter.

[toytuff]

Cool, thought that might be a little heavy. I'll go lighter.

Easy to change. CBX forks are 39mm (81/82 model) so maybe try a 10 weight?

tt

[bwaller]

Don't get me wrong I have progressive springs in one bike. However I bought a set of straight rate springs from Racetech and they are shorter to allow for preload spacing to properly set-up sag etc. It's the best set of 35mm forks I've used yet.

I was guilty of stuffing longer springs in our forks for years and riding around on lousy suspension. I have seen the light!  There are better options (emulators/springs) and lots of good set-up information available.

Whatever components you decide on, don't just stop with new springs and oil. There are easy fine tuning options that will allow your forks to work like never before.

[Deltarider]

I just rebuilt my forks on my '76 CB550 and used Progressives. 
Filled with 165cc of 15w fork oil...
 ... I'm 6'5" 215lbs

Is yours a K or an F?
If K, 165cc could be a bit too much, 15W could be a bit too thick.

My '76 500K2 (Europe) has the same front legs as the '76 CB550K. I'm as tall as you and tend to sit further back than shorter riders. I've come to the conclusion ATF (wt 7) is better for me.
Here's a question. At the bottom of the legs (on the sides) there is - just above the axle holders - a number stamped next to some sort of Japanese sign. What numbers do you or other '76 CB550K owners have there? I just wondered if numbers have to be identical left and right.

[alacrity]

I'm still in a quandary.  THe longer springs for a cb550k really do seem to be too long for the 72 Cb500k1 legs.  I have em installed and I've been riding around and even though they are a pretty soft rate and floating in honda atf (which I think is comp to about 7.5 weight in fork oil), it's pretty dang stiff.  I could just pull em out and cut the f'ers to size by slicing off enough of the straight wound end...

But I would need true/accurate measurement of unsprung stock OEM new fork spring in 72 cb500k1.  I haven't seen that measurement anywhere. In the manual, it describes amount of travel available (both comp and rebound) past center, but not unsprung length.  Oddly, it does say to measure the spring during service but doesn't give a value or a range (it does this in the 550 supplement -- but it also describes how the 550 fork internals have changed from the 500).

I wish someone had some NOS springs laying around to measure. They're apparenltly no longer available.

[dave500]

read reply #1!the length IS in the workshop manual.

[bwaller]

From the CB500 service manual for spring length

standard value 451.7mm (17.78")

servicable limit 425mm (16.73")

If you cut those springs they may fit better but will be stiffer, that's not the answer. One solution is Racetech for $125.


EDIT, sorry Dave I see you already posted lengths?

[Deltarider]

I'm still in a quandary.

I can understand that. If you dig into the Parts Lists you'll find Honda did quite some mods (front legs) over the models. But 500 and 500K1 seem to share the same springs. In the picture springs are shown with the tighter coils up, but I'm not sure if that is correct

[alacrity]

Whatever components you decide on, don't just stop with new springs and oil. There are easy fine tuning options that will allow your forks to work like never before.

Ok: I'm interested... what other suggestions do you have?
:-)

[bwaller]

Google suspension tuning. Check Racetech's or Sonic Spring's website for tuning info. It's all over the internet.

[Seeparkfly]

Don't get me wrong I have progressive springs in one bike. However I bought a set of straight rate springs from Racetech and they are shorter to allow for preload spacing to properly set-up sag etc. It's the best set of 35mm forks I've used yet.

I was guilty of stuffing longer springs in our forks for years and riding around on lousy suspension. I have seen the light!  There are better options (emulators/springs) and lots of good set-up information available.

Whatever components you decide on, don't just stop with new springs and oil. There are easy fine tuning options that will allow your forks to work like never before.

Did you use the emulators or spring only?