Starter Clutch Failures
Both of my KZ750 twin starter clutches have failed. One dramatically, one silently. They sure do seem to be prone to it…
750 #1:
The starter clutch exploded and seized my engine on my “first” 750 twin first. I was riding along at about 30mph in town when the engine just rapidly seized and the back wheel locked up. I got a handful of clutch and rolled to the side of the road. I pushed the bike home, pissed off. A week later I got around to checking out why…
It had automatically backed 1 of the 3 mounting allen screws/bolts out (the other two were already loose too), dropped a roller out, jammed against the starter sprocket or something and cracked in half. I was lucky it wasn’t worse.
This is immediately after removing the assembly from the seized engine. Note the melted screw head at top right. All 3 screws were loose and backing out. The pin and roller had freed themselves and wedged somewhere between the assembly, the starter sprocket and the engine case to cause the engine seizure.
Now from the other side, I hope you notice the housing cracked in half, the missing metal chip (hole in housing in foreground) I recovered (in background).
I just pulled the rotor, removed all the debris, got a replacement starter clutch from a spare KZ400 engine, removed all the pins, springs and rollers (only kickstart now), and reinstalled the *housing* only with RED Locktite on the 3 screws. So the final difference from stock is that it’s just missing pins, springs, and rollers. When you push the starter button, it just goes “Wheeee…”
Since I did this bike’s repair first, I naively thought I needed the housing as a spacer (of course, if I had it to do over, I would have left the housing out). More on that below…
750 #2:
So, shortly after, I was working on my *other* 750 twin; because I swore I would pull the rotor to examine the state of the starter clutch before that thing saw the road that season.
This time, after I pulled the rotor off, I was looking at what looked like the backside of a starter clutch, still on the starter sprocket. Lo and behold, it *was* the starter clutch. The three bolts that mount the starter clutch *to* the rotor had ALL sheared cleanly, separating it from the rotor. No shattering, no other damage, just a completely free-floating starter clutch. It looks like one of the three bolts was a little worn like it had been grinding like my other bike, but only a little. I’m sure this would have caused damage in the future… So I had to get the little bolt bits out of my rotor…
This is where all 3 screws were sheared, and the starter clutch was effectively free-floating in there. How long before one of the screw pieces got free and made it's way toward the crank? Fortunately, we will not find out.
For this bike, I left out the *complete* starter clutch assembly. This is because (as I mentioned above) I later realized that I do not need the housing as a spacer, but I *do* need the starter sprockets and chain to hold the sprocket steady while running.
IMPORTANT: I got some great advice over on the KTOF about an oil journal that exists on the crankshaft right under the starter sprocket. Without the starter sprocket in place on the crank, oil pressure might be reduced; by how much, I don’t know. Since I don’t want *any* reduced oil pressure, I put it in. And if the sprocket is on the crank, I may as well have the starter chain to hold it steady, and the starter to hold the chain, and the ankle bone’s connected to the….
Conclusion:
Now, all is well. And I can kick start them forever now. But do the pics make you cringe?
So is everyone going to go get a gasket (or make your own), a rotor puller (or rear axle), and check them out?
On a related note… If you decide to repair rather than remove, it appears as though Parts N More offers a starter clutch rebuild kit (though I’ve never bought anything from them myself).
Sorry if I sound like an evangelist, folks. But my engine seizing – even at relatively low speed – might have been my scariest moment in my brief motorcycle history…
Good info. I’m looking at buying a 1980 KZ 750 T. Like the classic retro look of the bike. Needs work so I’ll keep an eye on your site
Thanks
Drago
Hey there!
We PM’s each other a few times from the kz website, and I was wondering if there were any documented failures that you might be aware of with the CSR’s in this regard (the starter clutch failures?). Just wondering if they were ok with this particular model or not necessarily so?
Is the rebuild difficult should this be my course of action?
Thanks!
Chris
@Chris
If rebuild were to be necessary, it is incredibly easy once you have it apart, and if you have a starter clutch rebuild kit (as mentioned in the post above)… But sometimes the problem is not with the pins, springs, and rollers, but with the boss on the sprocket itself being worn un-evenly. And really on a lathe or a new sprocket will fix that…
Not sure if the CSR is affected like the earlier models. really, you should post that in the forum to see if any other CSR owners can corroborate or refute! But I would advise you check it anyway, if you have a spare weekend morning, and rotor puller, and a gasket.
Might you know of a step by step written and picture process of this rebuild/repair for the mechanically challenged minds…er….like mine????
Chris
@Chris
Actually, yes! The procedure for removing the sidecovers and rotor and starter clutch are all very well outlined in the Kawasaki Service Manual. You might have to hop around the manual a bit, but it has everything you need to know. Of course, if you are still confused by that after reading it through, make sure to visit the KTOF and we’ll help you there.
So did you just leave the starter motor in place? Also, I’m wondering where you got your the rotor puller and if you happen to know the size/thread pattern?
I saw the poor man tool post and I think it’s an awesome idea, I just don’t want to use my rear axle if I don’t have to.
Thanks!
@ Tony
Yep, starter is still there, as is both starter sprockets and chain. The rear-most starter sprocket is there due to needing to maintain oil pressure over the oil journal beneath it on the crank. The chain is there to stabilize the rear-most sprocket while running. The starter sprocket is there due to the chain. The starter is there so i didn’t have to plug the hole, and due to the rest behind it.
I got my rotor puller bolt from z1enterprises.com. I’m not sure now which size it is, but feel free to call them if their website doesn’t make it obvious, and they can help…
I hope that helps!
Been there, done that. Funny how my oil pressure light came on at idle in hot weather right after removing the whole starter clutch/gear from my crank. I’ll have to go back in there and look for the oil journal. Thanks.
I have a question about that (stupid thrust washer in your pictures) if you don’t mind, since you’ve done this more than once? I have a 77 b2 motor I’m using in another model. I had to replace the stator as it was dead. So I was of course checking that nasty starter clutch to make sure no bolts were lose or sheered off like you had.
However even with the manual I own, I can’t for the life of me see if that Thrust Washer is suppose to go between the flywheel and starter clutch, or behind the entire assembly against the block.
It appears by the manual to go between the flywheel and clutch assembly, yet every time I put it there and torque the flywheel bolt down to it’s 51-57 ft lbs it’s locking the assembly agianst the block and won’t let it roll over… my logic tells me it belongs behind the entire assembly agianst the block..
So would you mind helping a doh brain out? The manual mentions the washer twice, yet both descriptions and pictures don’t really show it in plain English I can understand.
@ Dave
Ah… I understand your confusion… but it’s actually pretty simple… The washer goes between the starter sprocket (that sits on the crank over the oil journal) and the rotor. It keeps the sprocket separated from the rotor so it does not bind.
If you look at the last pic in the post above, you can actually see it sitting on the sprocket right where it goes… It stuck to the sprocket as I removed it, and I left it there for the picture.
I hope that helps!