Sorting Clapped Out Front Suspension

Good afternoon fellow Z1300ers,

After 9 months I’ve finally got my “assembled basketcase” 1979 A1 back together, registered and on the road. My first rides of this bike established that the motor pulls very strongly and all now works as it should (except for the carburettor setup but that is for another time).

The most critical item needing rectification is the suspension. The OEM rear air shocks dislocate my vertebrae over every bump in the road, no matter what the air pressure or damping setting is. To remedy this I’ll go down the same path as I used to for my Kawasakis in the 1980s – Koni tri-rate rear socks (or Ikons as they are now). Easily sorted.

The front is a different story, however. It is as soggy as a bowl of watery porridge. Even under moderately keen braking, the fork dive is nearly 150mm (6 inches for Americans). Often the forks stay stuck in a partially compressed state. I’ve tried air pressure up to 10psi but am hesitant to go higher.

I’ve not had them apart yet but I’m expecting a tale of woe and despair when I do strip them.

In preparation for this I’m in the process of ordering wearable components but I do have a few questions that I hope I can seek some advice on (I’ve already looked up all the front suspension topics in the Tech Forum):

1. I’m intending to replace the fork springs with Ikon progressive rate springs.

2. The workshop manual specifies 391cc of 20W-50 oil for each fork leg, which seems heavy compared to the old BMWs that I’m used to. Any other non-Kawasaki sites refer to a whole range of recommended oil weights, typically 5W to 10W. What have other owners gone with?

3. Are OEM fork seals preferred or are there aftermarket ones that are a better design?

4. When searching for replacement parts, I often see inner/outer bushing kits available for the forks. I can’t find reference to the bushings in either the workshop manual or the parts catalogue. Is anyone able to help advise where these fit into the scheme of things?

5. Is there a better, cost-realistic option to the air over hydraulic system of the standard forks? I’m not after race suspension, just comfortable road use.

Thank you for reading this far. Any advice regarding Z1300 front suspension is greatly appreciated.

My 2 cents:From day one, the OEM rear shocks were inadequate for two-up and gear.  I replaced them with a pair of S.& W. air shocks.  With a “passenger” and no air PSI the S. & W.’s were too hard.   I haven’t had a “passenger” for years so went to these:

 

  I found these to be too hard!   I took them apart.  The nitrogen cannister has a bladder that separates the gas from the oil but the gas volume is so little; I found it useless for its purpose.  I removed the bladder and most of the oil.  They are installed with a cross-over and gauge.  With a small bit of spring pre-load and 20 PSI the ride is compliant and comfortable!
  Front shocks; 20W oil, 24PSI (on the center-stand) with a gauge and cross-over.   The front still dives with a firm application but is acceptable for myself.  A note here:  I’ve been riding with 24 PSI for YEARS (?) and have never “blown” a seal! 
(There’s a joke there but I’m not going to elaborate !!!)

Once I solve the engine part, if I ever do, I will have to adjust the shock absorbers, Christine behaves like a merry-go-round horse.

I was planning to buy this pair of Betor shock absorbers, the store where they are sold is just 8 km away. from my house.

BETOR SHOCKS


 

Unmentioned joke received and understood
I did read your write up in the Tech Forum about fixing these shocks -- good job. I bought a pair of non-piggyback JBS rear shocks for my little Z250A a few years ago and they were 'orrible! I'm sure the Ikon tri-rates will be fine.
Thank you for you comments regarding the front forks. Mine aren't linked but that's just a bit of extra faffing around. The 24psi is definitely interesting. Good to confirm the 20W oil.
Thanks!

That's a brand I've never heard of before.....
Similarly, Ikon are local (to me) manufacturers. I appreciate the heads up. Good luck with the engine.

OEM fork seals  vs. after market. One bike I have still has the original forks seals. 45 years old and still working. Another bike has All Balls. They make seals and bearings for this bike - quite popular as far as I can tell.

To up grade the front forks. Progressive springs probably a good up-grade . Zed-parts have Hagon .
The next step would be converting to a cartridge - type dampening system from someone like RaceTech. They are called Cartridge Fork  Emulators. Their idea is to provide adjustable dampening .