Starter Clutch Heavier Springs?

I've been battling problems with the starter clutch on my 1979 KZ750 for over a year. I've replaced the rollers, springs, caps, flywheel, just about everything.

It all looks fine and after reassembly works great for a while. But a few weeks or months later, the starter clutch will start to miss every once in a while, then get progressively worse until it fails completely. I've triple checked the torque spec on the flywheel bolt, it's spot on.

The springs in the starter clutch have always struck me as a little flimsy. They seem like ball point pen springs. I figured the engineers and Kawasaki knew what they were doing though and just replaced the old with new. But after chasing this problem so long, I've decided to try upgrading to some heavier duty springs.

I found some at the hardware store that are the right diameter. They're a lot stiffer but a tad shorter than the stock springs.

Just wondering if anyone else had tried upgrading these springs. When assembled the starter clutch still seems to function properly. I can turn it one way by hand, but not the other.

Is this a bad idea?

Hi Topper,

I'm pretty sure that the springs don't add to the engagement ( grab ) of the starter clutch. They just get the process started until the revs get up there and the centripetal acceleration forces the rollers outward compressing the springs. I have the same bike as you, 79 750 twin. I also replaced the springs and rollers and for a while the clutch worked as if it was new. It still works, it just slips once in a while. I did not replace the sprocket with the boss on it despite the fact that I could see some marks on it. Is that part still available from Ma Kaw?

Bill

Unfortunately, according to Kawasaki.com it looks like that starter clutch gear has been discontinued. Ed

I've seen the sprocket for sale before (haven't looked recently). My memory is that it was pretty expensive. I don't see any galling or marks on mine and I don't think the boss is worn down. Here it is:

You might be right about the springs not contributing to the engagement of the rollers, but I'm at the point of grasping at straws with this. Could heavier springs do any damage? I could imagine if they don't compress enough they might not release, but when turning by hand, they do release, so I'm hoping it's OK to try.

Thanks Ed,

Back in the day I had a job for a brief time with a company in San Diego that sprayed metal onto bearing surfaces for jet engines. The process was supposed to add a few thousandths of metal that could then be remachined till the speced size was attained again. Has anybody heard of this or a similar technology that might be applied to build up that gear/boss?

Bill

When at rest the springs push the rollers into a space that gets progressively smaller and as long as the relative rotation is in the drive direction the clutch is engaged. When I said I could see marks, they were more along the lines of polishing. If the size of the gear isn't so critical perhaps restoring some microscopic texture would help.

I'm thinking that heavier springs would only delay the release of the clutch, perhaps causing more wear on the gear (boss) and rollers.

Bill

KZCSI wrote: Thanks Ed,

Back in the day I had a job for a brief time with a company in San Diego that sprayed metal onto bearing surfaces for jet engines. The process was supposed to add a few thousandths of metal that could then be remachined till the speced size was attained again. Has anybody heard of this or a similar technology that might be applied to build up that gear/boss?

Bill

You think that's the problem? Is there a wear spec for that gear?

www.digitaltrends.com/cool-tech/ge-cold-spray-metal/

www.metallisation.com/

Not sure how affordable these process are.

Here's one way NOT to go about it.

www.lni.wa.gov/Safety/Research/files/ThermalMetalSpraying.pdf

Wow KZCSI, that's amazing! But I sure hope it doesn't come to that. I can't imagine that's very affordable and will probably make the NOS gear I let go on ebay look cheap.

I'm thinking that heavier springs would only delay the release of the clutch

I guess I'm kind of hoping that'll actually help. Usually when the starter clutch fails, I push the start button and I can hear it grab and start to turn the engine over, then it slips and releases before the bike starts.

I realize I'm grasping at straws here, but short of finding a NOS starter gear I'm not sure what else to do.

KZCSI wrote: Thanks Ed,

Back in the day I had a job for a brief time with a company in San Diego that sprayed metal onto bearing surfaces for jet engines. The process was supposed to add a few thousandths of metal that could then be remachined till the speced size was attained again. Has anybody heard of this or a similar technology that might be applied to build up that gear/boss?

Bill

I wonder if the boss could be lightly machined without first adding metal to it. Looking at Topper's excellent video (thanks Topper) the stater clutch assembly is tapered where the rollers contact it (see yellow lines in pic below from video). The image shown is a snapshot of the assembly when Topper is turning it counter-clockwise to show how the rollers tighten against the assembly. Even when the rollers are fully engaged, as they are in the image, there appears to be considerable space left to the right of each roller. So if the diameter of the boss was machined down just a few thousandths the rollers should still fully engage as they moved only slightly further clockwise in the assembly. If might be worth a try if a spare starter clutch gear is available. The second image below shows a new old stock starter gear for a KZ650. While the gear itself is different, the way it operates with the rollers is the same as the KZ750 twin. In the image you can see the original texture of the boss. Ed

Topper wrote: Wow KZCSI, that's amazing! But I sure hope it doesn't come to that..

I bought an entire good used starter clutch assy with sprocket and chain off one of the online dismantlers for something like $80. Turned out I didn't need it so I sold it to somebody here.

If you are replacing parts but still having problems, I wonder if your housing is warped or messed up?

Anyway, buying a complete assy might be better than trying to stick more parts into one that keeps giving you trouble.


The other KZ Twin forum has a ton of info about KZ starter clutch woes, but their server seems to be down.

www.armbell.com/kz400/viewforum.php?f=43&mforum=kz400