Clutch plate thickness...replace?

I'm in the proccess of rebuilding the top end of a 1982 KZ750 R1 I got for $250. I have never started or ridden the thing since owning it. The previous owner said it "needed a new clutch". Often that seems to mean that the clutch cable just needs an adjustment, right?

I went ahead and removed the clutch cover while in the proccess of checking out the lower end while I wait on the top end which is at the machine shop. I measured some of the fiber clutch plates with a micrometer and they measured about .153 in. thick. The wear limit is .14 inches.

Is this close enough where I would want to go ahead and replace them anyway? Or could I expect to get more life out of them? What is the thickness of a new plate?

ericvm wrote:

I'm in the proccess of rebuilding the top end of a 1982 KZ750 R1 I got for $250. I have never started or ridden the thing since owning it. The previous owner said it "needed a new clutch". Often that seems to mean that the clutch cable just needs an adjustment, right?

I went ahead and removed the clutch cover while in the proccess of checking out the lower end while I wait on the top end which is at the machine shop. I measured some of the fiber clutch plates with a micrometer and they measured about .153 in. thick. The wear limit is .14 inches.

Is this close enough where I would want to go ahead and replace them anyway? Or could I expect to get more life out of them? What is the thickness of a new plate?

I'd sure replace them. I think plate sets run maybe $80 or so a lot of places. I got mine from JC Whitney, Z1 might carry them. For all the work it is to repalce them, I'd chuck those. Be SURE to get new springs.

should I replace the metal plates?

ericvm wrote:

should I replace the metal plates?

I believe they can be reused as long as they are not warped or scored. I still have the originals in mine at 80k miles.

KZ650 friction plates are 3.7 - 3.9 mm thick with the service limit of 3.5 mm. That's .1457" - .1535" with a service limit of .1378". I would not replace them (unless they or the steel plates are warped). Just button it up, adjust the clutch, and try it. It shouldn't slip. Ed

ericvm wrote:

The previous owner said it "needed a new clutch". ?

Based on the specs, it sounds like the discs haven't lost much material. No big surprise, I think I replaced mine at about 40k and they didn't have much wear. My clutch was slipping BADLY and I ordered a new plate and spring set.

After doing the job, I suspect the springs were the main culprit. But, from what I've read, clutch plates with enough material can still slip because junk gets impregnated into the fibrous material. Maybe they can be sanded?

If the previous owner said the clutch was bad.... I'd probably shotgun the old parts out just to avoid a future headache. But I'm old and lazy.

bountyhunter wrote:

ericvm wrote:

should I replace the metal plates?

I believe they can be reused as long as they are not warped or scored. I still have the originals in mine at 80k miles.

if they aint warped toss em in a glass beading cabinet to knock the glaze off,this helps oil stick to them also;)

For consideration:

Performing the clutch pushrod adjustment is shown in the factory service manual (and owner manual) as required routine maintenance. Seems this is sometimes overlooked, ignored or simply disregarded in a headlong charge toward addressing the plates and springs for correction of a clutch slippage problem.

If the clutch pushrod gap has reduced or vanished (from perfectly normal ordinary gradual wearing of the clutch plate material), the simple quick cheap easy fix is often a clutch pushrod adjustment. The "other" fix is replacing the clutch plates, which returns the clutch plate material to "thick as new" thereby restoring the required gap in the clutch push rod (and without having to deal with the dreaded 30 second clutch pushrod adjustment :ohmy: )

Perhaps not the situation here, but where measurements after clutch disassembly are found within specs, boo on any failure to having first tried adjusting the pushrod gap :lol: .


Here it is, straight from Mama Kaw's lips :kiss: :

Clutch push rod adjustment -- Need and Purpose

The FSM covering Z1 and KZ900 includes a periodic maintenance chart requiring clutch push rod adjustment at 2000 mile (3000 km) intervals and explains the need therefor in separate text, which explanation is quoted verbatim as follows:

Besides cable stretch, clutch plate wear also causes the clutch to go out of adjustment, with a decrease in push rod play. Due to this wear, the push rod gradually moves closer to the clutch release lever (at the lower end of the clutch cable) until it touches the adjusting screw. When the rod is touching the screw and therefore has no play, the clutch will not engage fully and clutch slippage will occur. Note that the clutch push rod does not necessaily have play just because the clutch hand lever has play, and so hand lever play alone cannot be used to determine whether or not the clutch requires adjustment.

The FSM covering '77-'79 KZ1000's includes a periodic maintenance chart requiring clutch adjustment at 5000 km intervals, and explains the need therefor in slightly different language, which explanation is quoted verbatim as follows:

Clutch plate wear also causes the clutch to go out of adjustment. This wear causes the play between the push rod and the adjusting screw to gradually diminish until the push rod touches the adjusting screw. When this play is lost, the clutch will not engage fully, causing the clutch to slip.
NOTE: Even though the proper amount of play exists at the clutch lever, clutch lever play alone cannot be used to determine whether or not the clutch requires adjustment.

Good Luck!

Thanks. It sounds like my friction plates aren't actually that worn. I'll probably just try re-using them and making sure the pushrod and everything is properly adjusted.