KZ900 fork rebuild question, w/ pictures

I’m rebuilding a set of forks from a 76 KZ900. This is not my first fork rebuild, but there are some things here I have not seen before that have me puzzled. As a point of reference, the lower sliders do not have bushing inserts near the top. The tube rides right in the aluminum so that helps to pin down the year. Also the springs do not have tapered ends; further adding to the 76 vintage of the forks.

When I took them apart and pulled the valve assembly out, the 1.87 inch spacer shown below came out with the valve just as is shown. I have never seen this piece before. This effectively shortens the overall length of the fork, when fully extended, by 1.87. Extended length is approx 27½” with the spacer from centerline of axle to top of tube).


Since I think these are 76’s I thought maybe they could’ve been 900LTD forks thinking perhaps these were shorter for the LTD. After looking at the parts diagrams for the LTD & KZ900-A’s the diagrams are the same and the spring P/N is the same for both (item numbers differ between the two but P/N’s are consistent). The parts diagrams are a little weak IMHO on showing actual assembly sequence.

KZ900 Standard


KZ900 LTD


The spring fee length is 18¼ inches which is in line with a 76 fork. Clymer manual states min serviceable free length as:
1973 19”
1974-75 19.5
1976-77 17.9
1978+ chain 20.1

When I build up the fork with the spacer included, the spring extends beyond the top of the tube by about 1½” which, when assembled with a cap make a really stout front fork. If I remove the spacer, then the spring is approx ¾” below the top of the tube but I think it might be a little soft.


Just to add a little bit to the investigation, I pulled apart a different set of forks with a 19.5” spring length, did not install the spacer, and put in the 19.5” spring. It sticks out the top of the tube by approx 1 inch and total length (from centerline of axle to top of tube) is approx 29”.

After all that, I guess the bottom line 3 questions are:
1. Anybody seen this 1.87 spacer down there before?
2. What should the extended length of a KZ fork be?
3. Where should the spring end up, with respect to the fork tube, just prior to inserting the top plug?

Thanks in advance,
Hemicbx
York, PA

ive seen forks with springs that stick out,ive also seen them stuck in a little bit.i generally just put them back together the way they came apart if the springs are in spec.
when we went through the front end on skipper76s 76 900ltd his origionals were trashed so he bought a set of used ones that were supposed to have been rebuilt,when i opened them up one had a longer spring and the other one had a pvc slug in it to make up the differance! :S
so i gave him a matching set of springs i had from another set of forks and it solved the problem.
that reminds me has anybody seen him around ? its been a long time

Yeah, that's always the other part of this sort of thing: "Who's been into and done what to these forks over the last 34 years." I usually do the same, Plummen; put them back the way they came apart. These ones are just a little weird.

How do you tell if the springs are week and need to be replaced? Just by feel, or is there a proper test that can be performed.

Also for rear shocks do you adjust the springs by how the bike rides, or is there a method?

you measure free length on fork springs

Ohlins says

Front sag-
From completely unloaded to bike weight only - 25-30mm
From completely unloaded to bike and rider - 35-48mm


Rear sag
From completely unloaded to bike weight only - 5-10mm
From completely unloaded to bike and rider - 30-40mm

You will need two buddies to set it up. One to balance tie bike and one to measure. You will be standing nearby supervising or sitting on the bike, depending on which measurement is being taken.

id say just pull the springs and measure,much easier! :laugh:

The forks on my bike have an air chuck at the top?? I have contemplated rebuilding them my self since the last shop I had do it did a piss poor job.

If i put in progressive springs can i do away with the shrader valve?

The shop I had work on them said the air is to stop frothing of the oil ..

Just thought i would ask someone who has worked on these bikes that are older than me ! lol got to love that old school!

thanks
can you see the front end squat?? this slop is what i want to do away with . and im not just gona cut a piece of pvc to take the sag out of the springs

That looks like a spring pre-load spacer. It sets the forks to the optimal ride height based on rider/bike weight. It does not make the forks stiffer. It also may not be correct for you unless you are the same weight as the previous owner. To determine the correct preload and spring rate, take the following measurements.
A. No load - front wheel off the ground
B. Static - Bike weight only
C. Ride - Bike and rider in a normal seated position.

TexasKZ provided Ohlins recommendations of:
Front sag-
From completely unloaded (A) to bike weight only (- 25-30mm
From completely unloaded (A) to bike and rider (C) - 35-48mm

Add the appropriate length preload spacer to achieve A-C = 35-48mm.
Then, If A-B = less than 25, you need a stiffer spring (and less preload)
If A-B = more than 30, you need a softer spring.

Measuring the spring length removed from the bike will only tell you if the spring has weakened from the original factory specs. Since the factory took a guess on the average rider weight when they designed the bike, chances are it's not going to be right for you. I wish I still weighed what I did in '76.

finaly some sort of way to see if the springs need replaced how much for a set and where do i find them??

Also having alot of dive when braking is this normal it dont feel right and im not all that heavy at 185 .

should i try the pvc spacer?? sounds like a cheep fix and with some tuning it may work??

Sorry for blowin up the thred just wanted to chime in for some advice its so good here. as always thanks

try heavier fork oil if your springs are in spec

Heavier weight oil will increase both your compression and rebound. The fork will not dive under braking as fast, but it will also rebound (uncompress) slower. That may or may not be a good thing.
The shop that told you the air was to stop the oil frothing doesn't do much suspension work. Technically, air is what causes the oil to froth.
The air acts in conjunction with the mechanical spring.
Oil does not compress. Air does. Just like a spring, as pressure increases, so does resistance. It also pushes back with equal pressure. Increasing the oil level decreases the available air volume. Less air volume makes it is more difficult to compress (stiffer). You can also "preload" the air pressure. That's what the shrader valve is for. Inflate your forks with 1-2 psi of air and take it for a ride. If your forks have 5psi to start with, it takes that much more force to make them dive.
Small changes make big differences in suspension tuning. Do everything in small steps. To much oil or air can turn your forks into solid rods.