KZ1000/1100 clutch springs

It will be time to change my first oil after the rebuild of my engine. Since i used brake in lube on the cam surfaces and the pistons, I will be taking the clutch apart to clean it from all of the Molly and other junk that is in the lube (now in the oil) The clutch has been slipping like crazy and I would like to change the clutch springs. The bike has the original 1981 clutch springs in it and springs go bad with time. I do have a set of super heavy duty springs, but they are .136 wire thickness, in comparison to the .1 stock wire thickness. This is a bit to heavy for the street. I ordered a set of EBC CSK7 springs which are supposed to have only 15% more tension. Has anyone used these springs on their bike? They should be the same for all of the KZ650/750/900/1000/1100 bikes. i would like some input. i could have bought some stock springs from Z1 for about the same price. And since APE has no specs on their springs listed on their sight i stayed away from them.

Otto

A lot depends on the rebuild. Stock rebuild or did you pump some extra HP in there? Personally, I wouldn't run the HD springs unless I had too. Definite difference in lever pull. Don't know about the springs you bought. I would just pull the clutch, clean them, de-glaze them to be sure and then give them another try. Just doing that will make a difference lots of times. If after cleaning the plates and roughing them up, it still slips, use the slightly heavier springs.

The bike has a LOT of extra HP built into it. It was on the dino and read 147 at the rear wheel. I am positive that the old 1981 springs are week, that is why I want something new but I did not want to put in the ones I have because i used to have them in my 1105 Z1R and in city driving they are murder on the left hand. I was just wondering if anyone had experience with the EBC springs. I already have clutch plates ready to go in, which i de-glazed today.

No one here has used EBC clutch springs????

Your only recourse besides running the heavy springs is to run a lock-up so you can use either the stock springs or lite springs and have the lock-up do it's thing on the top-end and/or higher rpm's. This will give an easy pull at the lever and more clamping force when it's needed. OR...just use the springs and see how they work. As you know, it doesn't take much to replace them later.

Someone with a better memory may help, but I vaguely recall on the 900 models being able to use oem valve springs instead of oem clutch springs to provide additional spring pressure for a tighter grip without undue increase in lever pull.

Could be wrong, but thinking valve springs are better quality and last longer than ordinary clutch springs.

Good Luck!

Well- I just checked an inner OE valve spring and it is only .050 larger in OD than a clutch spring. It is also made out of .012 thicker wire than the clutch spring. The valve spring is .185 longer than the clutch spring but even if I compress it .185 it is still softer than the red springs I have and quite a bit stiffer than the stock clutch springs. I should have the EBC springs by Saturday, it should be interesting to compare the valve springs to the EBC. Now the main question will be if the extra .050 will fit in the pocket properly. Thanks for the hint Patton. I will keep you guys posted, with what I find out.

otakar wrote:

The bike has a LOT of extra HP built into it. It was on the dino and red 147 at the rear wheel.

I'd be hard pressed believing stock springs could handle that.

otakar wrote:

Well- I just checked an inner OE valve spring and it is only .050 larger in OD than a clutch spring. It is also made out of .012 thicker wire than the clutch spring. The valve spring is .185 longer than the clutch spring but even if I compress it .185 it is still softer than the red springs I have and quite a bit stiffer than the stock clutch springs. I should have the EBC springs by Saturday, it should be interesting to compare the valve springs to the EBC. Now the main question will be if the extra .050 will fit in the pocket properly. Thanks for the hint Patton. I will keep you guys posted, with what I find out.

I thought it wasn't just wire diameter but also tempering of the steel that determined spring rate?

The temper depends on the alloy of the steel. There is an optimum temper for each alloy. The valve springs would be made out of a better alloy if anything. The valve springs must be made out of an alloy which will not work harden.

I just did some preliminary spring tension tests. Now here are the test and book results. According to the Kawasaki manual.

Stock springs 55PSI@ 23.5mm compression (book Spec)
hi performance ? 90PSI@ 23.5mm (65psi@1") comp.(as measured)
valve spring 51PSI@ 23.5mm comp. (as measured)
old stock spr 50PSI@ 23.5mm (38psi@1") comp.(as measured)
EBC spring TBA 23.5mm comp. (as measured)

I will post the EBC spec once I get them and can measure them.
It is obvious that using a inner valve spring would be as bad as an old clutch spring. The valve springs are actually softer than clutch springs.

otakar wrote:

I just did some preliminary spring tension tests. Now here are the test and book results. According to the Kawasaki manual.

Stock springs 55PSI@ 23.5mm compression (book Spec)
hi performance ? 90PSI@ 23.5mm (65psi@1") comp.(as measured)
valve spring 51PSI@ 23.5mm comp. (as measured)
old stock spr 50PSI@ 23.5mm (38psi@1") comp.(as measured)
EBC spring TBA 23.5mm comp. (as measured)

I will post the EBC spec once I get them and can measure them.
It is obvious that using a inner valve spring would be as bad as an old clutch spring. The valve springs are actually softer than clutch springs.

It is obvious that using a inner valve spring would be as bad as an old clutch spring. The valve springs are actually softer than clutch springs--- possibily incorrect.

valve spring 51PSI@ 23.5mm comp. (as measured) --- is believed under the service limit for 77~79 KZ1000.

FSM for Z1~KZ900 provides free length specs for both clutch and valve springs without mentioning the psi designed for any particular compressed length. For example, the clutch spring free length is supposed to be 1.33 inches with service limit of 1.27 inches, and the smaller valve spring free length is supposed to be 1.42 inches with service limit of 1.38 inches.

FSM for 1977~1979 KZ1000 provides spring tension specs at particular lengths for standard limit and service limit of both clutch and valve springs, and without involving free lengths of the springs. For example, clutch spring compressed to 23.5mm is supposed to have spring tension of 23.5~26.5kg with service limit of 21.5kg. Whereas, smaller (inner) valve spring at 23.6mm test length is supposed to have standard spring tension of 26.20~28.96kg with service limit of 24.7kg.

Clutch spring at 23.5mm with standard tension 23.5~26.5kg and service limit of 21.5kg,
compared to
Valve spring at 23.6mm with standrd tension 26.2~28.96kg and service limit of 24.7kg

Indicates that the valve spring is slightly stiffer (i.e., a little stronger) than the clutch spring -- not weaker than the clutch spring.
And likely made with a more durable alloy.

The basic idea back then was an inexpensive method to gain slightly stronger clutch performance without a dramatic increase in squeeze pressure required at the handlebar lever.

Had the valve springs weakened the clutch action so as to allow more slippage under hard acceleration (instead of less slippage), the hot-shoe guys would not have favored the substitution.

It would be interesting to see actual test results between the clutch and valve springs with compression measured at 23.5mm.

With high performance springs of almost double the pressure, may soon develop Pop-Eye forearms. :laugh:

Good Luck with whatever springs are selected and fitted.