PO converted fork to progressive?

Hello,

I am so close to putting my kz750 back together and riding it-- hopefully this week if nothing new crops up.

One of the final mysteries I'm looking at is what the PO did to the forks.

Clues:

• Both valve stems were crushed, seemingly intentionally, and do not hold air
• See the attached image, this is what came out of the forks- ~19inch springs, spring guide, spring spacer, washer, small section of pvc pipe

What I need to know-- is this a progressive spring conversion?

If so, do the fork cap valve openings need to be sealed?

If so, and I can't find a small metric bolt to put in them with o-rings, is there an aftermarket cap I should replace the OEMs with?

And... any other general advice? Which fork oil? How much?

Thank you!



EDIT: corrected OP to PO-- too much reddit.

EDIT2: is the tightly coiled end of the springs supposed to be at the top of the forks? They came out tight coil bottom, but most installation videos I've watched show them being installed tight coil top.

It doesn't matter top or bottom. The caps have to be sealed. Your MANUAL will tell you how much oil it takes.
Steve

Thanks, I wasn't sure if this was a modification that required a different amount of oil.

If possible, I would remove the crushed air valves, then plug the holes with a threaded plug or something. Or, especially if they're ruined, replace the fork caps with the type without the air valves --- I'd guess the 70s 650 fork caps would work, but that is just a guess. The fork tube size should be the same ---- 36mm.

Those have the tighter bottom coils to I guess they are progressive springs. Those spacers look quite long to me, check with the manual parts diagram...nothing wrong with increasing the preload though,, if that's what you want.

The air valves on top are for adding air pressure, later ones have drilled fork tubes to allow a link pipe to balance the pressures.

I used about 250ml of 15 weight, I'd go 20 next time.

The long metal spacers are probably stock. The Progressive springs are shorter than the stock springs, so the po added the pvc spacers & washers as suggested by progressive. I'd check to see if he got the length of the pvc right.

1981 KZ650-CSR w stock fork springs --- the spacers are the same as the 750H Ltd.

Usually there's one rate spring in place of the spacer, then your long spring. If you installed a progressive spring with the stock short spring, you're defeating the purpose. So they eliminate the small spring. The 2 springs provide a "progressive-type" fork.

Your assembly would be: long spring, washer, short spring, washer, cap.

The only other spring in the 750H forks is the rebound spring at the damper rod.
Every KZ fork I've seen is pretty much the same ---- 1 rebound spring & 1 fork spring.

I couldn't find a parts diagram for that bike but I have taken forks apart (forget what model) and they have 2 sets of springs. The short one is a lighter rate, once that compresses the force is transferred to the main spring.

martin_csr wrote: If possible, I would remove the crushed air valves, then plug the holes with a threaded plug...

Ditto. That's what I'm going to do. Just plug the caps for now. I'm rehabilitating the bike to get it road worthy... it will get the full rebuild when I finish my Virago.

Tyrell Corp wrote: Those have the tighter bottom coils to I guess they are progressive springs. Those spacers look quite long to me, check with the manual parts diagram...nothing wrong with increasing the preload though...

I used about 250ml of 15 weight, I'd go 20 next time.

Thanks, I'm gonna try 15W to start. When I removed the caps, with the wheel jacked off the ground and the forks fully extended, there was still enough preload to eject the caps if I hadn't been cupping them.

martin_csr wrote: ...I'd check to see if he got the length of the pvc right.

Can you elaborate on that? What do I check this against? Do I need to know the manufacturer of the springs or is there a general xyz for progressive springs?

martin_csr wrote: The only other spring in the 750H forks is the rebound spring at the damper rod.

Your comment made me realize something that had been confusing me for a while. I think the PO swapped out 750H forks on a 750E model. I was having a hard time reconciling manual variations around the fork... making me go, "is this an H or an E???" The VIN comes up as an E2... but those ARE forks from an H, right?

Imma think I'm just going to have to put these back together as best as I can and evaluate the ride. I saw a nice troubleshoot guide somewhere in diagnosing the feel of the front suspension and remedies.

Thanks, everyone. I'll keep checking in if you want to just... talk at me. I'll soak it up.

[EDIT] I realize I didn't actually include the exterior fork components to judge what model they're from... but my fork tubes have the pinch bolt on one side, and the retaining bolts are accessible without removing the wheel... maybe not an H... but... a LTD? Honestly, I don't know... so some model variation education would be great for me. If there's good online literature, you can just point me there, and I'll read up on it.[/EDIT]

[EDIT2] My forks look identical to Martin's image. [/EDIT]

The 750E should have center axle forks. Since yours has the pinch bolt, they're probably the leading axle type found on the Ltd models & could be from a KZ750-H Ltd. The 750 shaft drive models have leading axle forks as well, but they have an air balancer hose between the upper tubes.

As for the pvc spacers, the Progressive Suspension website might have the info. I'd guess the new springs plus spacers should be the same length as the stock fork springs --- you'd probably want to use the max free spring length listed in the service manual for a 750H. just a guess. ???

Here's a site w a pdf manual & wiring diagrams. mbsween. bike-night. KZ750L3 . Scroll down & click "The Bible" link.
Note: some of the wiring diagrams are mislabeled in the links: the 1981 Ltd is an H2, the 82 is an H3, & the 83 is an H4.