Topic: progressive spring questions (with pictures)

[nomad]

Bike: '74 CB750K

I'm rebuilding my front forks using progressive springs and have a couple of questions.  I searched, but didn't happen to find exactly what I was looking for.

First, preload.  The stock springs are roughly 1/2" shorter than these new progressive springs (sag for sure).  The instructions say to use the spacer when I install the new springs.  Should I install the spacer now, or wait for the springs to sag a bit and put them in at a later date?

Measuring the cap, spacer and washer, that gives me roughly 2 1/4" of preload.  That seems like a bit much.  The cap alone gives me just under an inch.  Am I wrong?  The new spring with no preload is sitting just below the top of the tube (the included flat washer makes it level).



Next, from what I've read, it seems that it doesn't matter which way you install the springs... tight coils down or loose coils down.  The only question I have regarding that is, doesn't that alter the amount of fork oil you put in?  It seems that the tight coils would displace more oil and the loose coils less, requiring different amounts of oil depending on the direction of the springs.  Am I just over thinking this?  The shop manual says to use 7.0 to 7.3 oz. of oil on the stock springs.  I've read where some have used as little as 5.5 oz with the progressive springs.  So, is the answer somewhere in the middle or should I err on the side of caution and  go with 5.5?  I really don't want to blow my seals!



Thanks for any insight you can share.

[Steve_K]

I just put those in my 73 750K and I put the close spaced springs in first and used the the washer and then the spacer.  Good challenge to install the fork caps.  Be sure that the tank is on the bench.  Could dinge the tank while putting the fork caps in.  On fork oil, be sure that you have oil covering the damper after stroking the fork several times to bleed out any air.   I use oil level in my forks, but I am too lazy to go out to the shop to see what I used.  Trust Progressive to steer you right on the installation.
Steve

[grcamna2]

I see what you mean nomad, about the tighter coils possibly raising the fork oil level a bit inside the fork tube...the tighter wound coils will displace more volume in the bottom of the fork leg where the oil is.
I never considered that before and it's a good point. 

I'd like to hear from a few others to see what they have to say about it...whether the oil level height is critical in there..or just having the correct amount of oil in the fork. ??

[Danno]

you need the dampers covered at least however more oil means firmer/harder ride and the point of using progressive springs is to make a better riding and or handling bike so you can't go too far wrong with the stock oil quantity however some people are pickier than that and want the most they can get out of their spring kit

[nomad]

I'm going to call Progressive Suspension on Monday just to make sure, but I think I'm going to adjust the oil level to 150mm (PS recommends 140 max) and install the loose coils down.  I just ordered an oil level tool (I'll need it for years to come so I figured why not) to make things easier and more accurate instead of wondering about the exact number of ounces to pour in.

[bwaller]

Too much oil will limit travel too, it's a little trial & error just like finding the right viscosity. I have a slender neck turkey baster that works well for the job. Normally a springs tighter winds are away from point of contact, ie next to cylinder head or fork cap.

[grcamna2]

Too much oil will limit travel too, it's a little trial & error just like finding the right viscosity. I have a slender neck turkey baster that works well for the job. Normally a springs tighter winds are away from point of contact, ie next to cylinder head or fork cap.

Thanks for that bwaller..I needed to understand that better also  .

[becken]

http://racetech.com/page/id/30
These people don't care much for progressively wound springs, but this FAQ section can point you in the right direction for setting up your suspension.

[bwaller]

I have a set of straight rate RaceTech springs in 750F2 forks on my race bike. They are shorter and smaller diameter. As a result this allows for more oil & ample space for emulators and preload spacers.

[Steve_K]

Race Tech likes straight rate springs because when used with emulators, the emulators control compressive damping.   The progressive rate springs are supposed to help with that.  I can say that emulater and Race Tech springs work very well.  I have used them on my GIXXER and SV650 that have similar dampers like our Hondas.  Spring preload is important and I adjust after riding.  I rate the Race Tech system very highly and fork action as good as a VFR and several other latter model sport bikes.(street use only) I wanted to try Progressive springs to compare and later I will report on my experiences.
BTW, after improving the forks,  you will notice that the rear shocks will need help.
The feel that you want may take some time to sort out.  It will be worth it.
Steve