Topic: Progressive Suspension fork springs question

[emlupi]

So, I decided to freshen up my fork springs with a set of Progressive Suspension springs (1972 CB750K2). Everything is going along smoothly until it is time to install the spacers. According to their installation instructions there should be about 1 inch of preload on the fork springs. This is the depth of the stock fork caps on my K2.

However, the instructions also state that I should use the enclosed chart for the proper spacer length. The chart says to use the spacer provided in the kit on my K2. This spacer is 2-1/8 inches long. That, combined with the fork cap bolt, will provide a preload depth of over 3 inches.

On my bike with the fork legs fully extended (bike on a jack with front wheel off the ground) the new springs are down 1/4 inch from the top of the fork tube. This would suggest that I need a spacer of approximately 1/4 to 1/2 inch to provide the proper one inch preload for the springs. One thing is certain, there is NO WAY I will be able to stuff the kit spacer, washer, and fork cap bolt down into the fork legs at it's present length.

I would appreciate if anyone with experience installing these kits would give me a little guidance as to the proper course of action here. I don't want to have to tear this down again later because of improper installation. Thanks as always.

[scottly]

How long are the new springs? On my K1, the stock springs were 16 1/2" long, with steel 2 7/8" spacers. If the new springs are close to the old springs, perhaps a PO installed the spacers first, instead of on top of the springs? K1 spring is in the middle in the pic.

[emlupi]

The factory springs did not have any spacers and are the same length as the new Progressive springs. I am thinking that the spacers are not necessary for my installation. These springs are made for several different models of bikes, I guess some of those applications will require the use of the spacers. That's the only thing that makes any sense to me.

[scottly]

HOW LONG ARE THE SPRINGS? Sorry for shouting. If the springs are about 16.5" long, some numb-nuts installed the stock steel spacer down into the fork tube instead of on top of the spring where it belongs. If this is the case, you may be able to fish it out with a magnet...

[PeWe]

The Honda fork caps have a spacer function that will preload when tightened. I have used progressive springs without spacer, last time around 10 mm high since I thought without was too soft. The handling was OK without.

I have now (since a month) another type of progressive springs, German made (Wirth) exactly same lenght (I compared side by side before installation), instructions mention nothing about spacers.
One important thing is to replace the plastic piston rings that must make a difference. I replaced rebound springs too if that will make a difference. The new felt like my old when pressing them between my fingers. Later fork, K2-K6.

Lenght of springs 485mm (19,09") I measured my old Progressive springs from the company Progressive....

One more detail is that the Wirth progressive springs recommend max oil level of 160mm with collapsed fork with no springs in. Measured from top.
Progressive have 140mm as abs max but recommend the specific bike spec.

I installed my new springs with the 160mm oil level, new piston rings and rebound springs. Fork oil SAE 10, before 10-30.
Interesting to feel a difference when all snow is gone.

The lower fork legs were full of dirt, oily goo. I cleaned them with naphta, the bottom pipes lifted. Easier to do when fork oil seals are removed before new are installed.

EDIT: My shocks are IKON setting 2,2. Steering damper installed too. Stock swing arm and needle bearings, tapered roller bearings front.
I'll see if I need to install the spacers again.

[emlupi]

Scottly, the springs are 18-7/8 inches long. THERE ARE NO SPACERS IN THE FORK TUBES!! Sorry for shouting.

[emlupi]

PeWe,

Thanks for that info. The Progressive springs are of factory spec (19.075" with a serviceable limit of 18.11")) in length so I don't believe that the 2 inch spacers are necessary for my particular installation.

The forks were disassembled and cleaned thoroughly. I replaced the damper rod pistons, copper seal washers, fork seals, boots, etc. I also followed Progressive's instructions as to using the factory spec oil volume.

I am going to set these up with the recommended 1 inch of preload. If the ride feels too soft at that length it will be fairly simple to put a longer spacer in later.
Thanks for the replies.

[Yamahawk]

That's a good upgrade for your suspension! I believe that any bike can benefit from having the stock springs replaced, as they are usually too soft from the factory to begin with. And, after 46 years of living in those tubes, they have lost some of their strength, making them even less effective than when new. Would love to hear how much better they are now, once you get a chance to road test them!
Charlie

[Pwrwagontom]

I realize this is a zombie thread...but I figure I'd try it instead of posting on the same topic again.

OP- how did this conversion work?  I have a progressive spring set ready for install in my K2.  Did you find the bike to handle OK without the spacer as discussed?  Did you find that putting the tighter end down decreased noise like the instructions say?
Lastly, did you notice any change in the amount of fork fluid that you needed to use?


Thanks!

Tom