Kz750 starter clutch repair failure

5 years later:

So, after very few rides and miles on the bike (less then 1000km - this is not a regular ride), I have the same problem. *sigh*

I've wondered if the primary chain could be the problem, as I have had primary chain slap on the bike since I bought it (2nd hand of-course), could the chain slip on the gears of either the crankshaft or secondary shaft, or am I just being daft?
Broken gears on either shaft?
I don't think this could be the case, as the problem starting the bike as fixed with the replacement of the clutch housing - so there must be something I have missed. 

I may have to open her up again, remove the starter clutch again, and inspect. I just am not sure what to look for, and if there isn't perhaps something else completely that I am missing. 

When trying to start, you can hear the starter turn the engine and then let-go and spin. 
I will try to take a video, but its exactly what you would expect and can see elsewhere from a failed starter clutch. 

I've not read back through the thread but if you only used a repair kit and not replaced the whole unit then you were lucky it lasted 1000 miles.  You need to replace the whole starter clutch and possibly the starter gear to get good results.
A worn starter gear will chew through a new starter clutch unit in fairly short time. 
 

Found this topic, and the replacement of the housing for the pins and rollers was the problem for this chap. 
perhaps my issue too:  kzrider.com/forum/2-engine/608618-help-1...utch-issues?start=24
 

I have found a second hand parts dealer who has a whole unit with sprocket for me. Its not cheap, and I am second guessing myself.
I really don't want to have to deal with this issue again in the future.

Some questions,

1. How can I be sure this one will work, what should I look out for?
2. Do you think it would be of any value, to simply remove the sprocket (assuming its the offending part) and have the surface of the contact area machined flat again? The rollers on the housing are on springs, and there should be some tolerance. 
3. If machining is a bad idea, what about building it up somehow, is that even possible?

Any advice would be appreciated, I miss riding her. 

Click on the picture I posted and zoom in on the "new" one. It's not a flat surface so machining the old one flat is not likely to work.
Buying a second hand one will be a waste of money it'll likely be the same condition as your original. 
If you want to fix it properly so that it'll not cause issue going forward bit the bullet and buy both the starter clutch and sprocket new. 
Half assed fixes on pieces like this are a false economy. You'll just be doing again in short order at best. 

Thanks Warren, 

Where would you suggest I buy it from then?

Of all the bikes I've ever worked on or rebuilt, I've never seen a starter clutch hub with those lines in them as shown in the NEW photo.  The clutches always look like the USED photo, including the clutch in my 750, and they always work fine.  I guess it's a matter of degree; if the vertical grooves are too deep, the rollers can't bite into the hub.  Maybe take a flat honing stone and knock off the high spots?  Or get a new hub, if you can find one.  At minimum, get new OEM rollers and springs.  That's what I did.

Phil at zpower will post worldwide. 
www.z-power.co.uk/starter-clutch-gear-z650750
www.z-power.co.uk/starter-clutch-assy-1062

Check out ditching the stock for a starter clutch from a ZR7. It's a bolt in swap. I know it's had a thread ot 2 about it in the 6 speed transmission swap and maybe on its own.

No offense, but it is not a "bolt-in swap" from the ZR7's.  .....This is changing from a roller type clutch starter to a sprag type one, ....and they are physically different.   The whole secondary shaft and oil pump need to be swapped as well. 

 Although it is worthwhile if willing to find and spend the money on the parts.

I put one in my '82 KZ750 H engine. One does not need to use a ZR oil pump.If one does, it has been suggested to use the ZR oil pressure relief valve.You do need to use a (I think) a pre '05 starter clutch. I put them side by side and they are almost the same size. Use the appropriate spacers to locate the SC. I could have used the stock shaft but, the ZR shaft is thicker in places. I got it with the SC in the ebay win.

Thanks for your replys guys,

I initially replaced just the rollers and pins, that didn't last long at all, then I replaced the entire clutch (not the sprocket - at the replacement parts one looked worse) and new rollers and pins and that only lasted 1000km. Is machining the sprocket is an option, and I'd then replace the rollers incase they have been chewed through by the sprocket. 

Looking at he prices for new parts, wow, and I am in south africa and would have to have them shipped which isn't cheap either. 
Concerning the conversion to a ZR7, I don't understand what the benefit would be?