'81 GPz 550 clutch slipping.

So I was able to ride my new to me bike for the first time since I bought it a few weeks ago.
It runs great now but the clutch is slipping on hard upshifts only, it will catch again if I let off the throttle.
Rolling on the throttle or snapping it wide open while already in gear and it holds fine.

I've adjusted it by loosening the lock nut on the clutch adjustment, backing off the adjusting screw until I feel resistance and then screwing it back in 1/4 turn.

Anything else I should look at before I order a clutch.

Using 10w40 non synthetic motorcycle oil.

Wait a minute. Screw it in until you feel resistance, then back off 1/4 turn. Loosen the cable all the way first. Have you lubed it? You may want to take off the cover and grease the actuator too.
Steve

Yes, oil level. In my experience, the time when a clutch begins to slip is right after an oil change. Even the manual states a high oil level will cause slippage, so check that first.

Also, in all of the 550 bikes I've owned or worked on, I have yet to find a clutch disk that measures below the service limit. I've also bought aftermarket disks that came thinner than old factory disks. So you likely won't need disks.

Steel plate warpage is not very common unless it's been run while slipping for many miles.

The springs do tend to lose some pressure over time. That is usually the only wear I can find.

Once you have the clutch apart you can do what I think is the single most effective thing I've done to the clutch:
If you notice, on the steel plates, one side is sharp and the other is rounded. If you stack them so all of the sharp edges face one way, the clutch tends to grab harder, but also has a harder time releasing. If you stack them the other way, the clutch releases nicely, but slips a bit more. I found an old set of plates and just very lightly rounded the sharp edges (interior teeth) with a wire wheel. That set worked best of all. It grabbed nicely and released just as nicely. It makes sense since the plates' teeth can move easier on the hub splines. I also did the other things you would consider, such as taking super fine grit and polishing the wear marks on the basket fingers and hub splines. This did help a little as well.

After going to pods and rejetting, I was still getting some major slippage. I ended up putting small shims under the springs. The heavier duty springs were just way too stiff for city driving.

After you check the oil level, you may want to double the check the clutch adjustment since it's easy to do. The manuals are vague/wrong for the newer type actuator.

Here's a link to some details on the clutch adjuster, in case you haven't already seen it:
gpzweb.s3-website-us-east-1.amazonaws.com/ClutchReleaseMech.GIF

I'll add it as an image, but you might need to download it to read it.

On the 81 gpz you unscrew till you feel resistance then retighten 1/4 turn.
At least per 1981 supplement.

Clutches will slip more in the higher gears. You should check it in 5th or 6th gear, roll it to WOT, and high RPMs. That will show if the clutch is slipping due to weak springs etc. If not, then it's more likely an adjuster issue or possible bent push rod, or even just the cable having resistance.

If you do take it apart be ultra careful with the spring loaded bolts. They love to strip out. I go about 10% under torque on those. And make sure to tighten them in many steps, in sequence to load them evenly.

Thanks Lou, I did just chance the oil, no idea if it slipped before because I didn't ride it hard at all until today.
The oil is right at the top line on the sight when its on the center stand, I'll start there.
I'll get achance to ride a bit tomorrow although it will be cold.

Love the little bike so far, thanks again for the info.

New stock Kawasaki clutch springs and rough up the OEM steel plates with a DA and 100 grit sandpaper. Clean the plates really well, reinstall with plates with fresh springs, and there is about 90% chance you will ride off into the sunset.

Oh, and get a fresh clutch cable while you are working on the bike and lube the clutch release mechanism. The clutch will feel like butter afterwards.

Forgot I had these photos.

By getting the tires about 3 inches off the ground, and simply setting it on the sidestand, I can open the clutch without losing any oil. Obviously the angle will depend on many factors like suspension, and on this bike, the side stand perch was replaced. It was removed for racing and I had a new one welded on, so the angle could be different from stock.

Also a couple photos of the plates where I hit the tooth edges with a wire wheel. (Did not let the wire wheel scratch the actual disk-mating surface.)

As Nessism says, you probably will be fine without buying plates or disks, but be careful with scuffing plates. I did that very lightly with 220, I think, and it was way too grabby especially on hot days in traffic. It would make the bike creep pretty heavily while holding the clutch in first gear, and would really slam hard into gear.

Maybe just scuff 2 or 3 plates and see what happens.

I polished the gasket surface and used a new gasket with antiseize about 10 years ago and have had the clutch cover off probably 10 times since, with no scraping and reused the same gasket without leaks.

Perfect.

Tonight I drained a bit of oil out, just shy of the top mark on the sight.
I also readjusted the adjustment screw using 1/2 turn instead of just the 1/4 that I saw in the manual.
I also lubed the clutch cable itself and the pivot point on the bars to cure a little squeak it had.
It's actually much smoother now. The way it was acting (not slipping during high gear roll on but on quick upshifts) I think its possible that it was just dragging a bit.
Tomorrow I'll ride it around and see what happens, if it still slips I'll pull the clutch apart and see what's what.

Thanks for the help everybody, I'm glad there's a good following with these old bikes. My older brother (he's 60, I'm 40) has worked on bikes his whole life and always has no fewer than 25 motorcycles on his property took this thing out today and came back with a huge grin commenting on how much fun they are.
With help from this community I hope to get this thing running tip top and enjoy it this summer.

I'm sure you will.
Steve

You must not be using a Kawasaki Service Manual. You do NOT turn the adjuster tighter (in) after it just makes contact, and you do not turn it 1/4 turn. You turn it LOOSER (out) by 1/2 turn. Turning it tighter (in) means the clutch will never fully engage. Here's what the Kawasaki manual says:



Ed

Turn counterclockwise until it becomes hard to turn.

Then CLOCKWISE 1/4 turn.
Per manual included with the 1981 gpz550

Per this manual it says 1/4 turn, apparently there's a manual that says 1/2 turn, both indicate clockwise.

Make sure you are reading the 1981 supplement.

Here are some pics that I just took of the original owners manual located under the seat of my bike.