kz650 starter clutch solution - ZR7S part

The Zephyr, ZR7 bikes took the kz650/z650 engine & transmission and slowly improved it over 2 decades.
One z650 weak point is the starter clutch. People change rollers, springs, but it appears that the most common issue are several things.

1. Low cranking battery
2. Synthetic oil or oil additives
3. Weak springs
4. DENTS IN THE ROLLER RAMPS

The rollers are the only hardened parts in the centrifugal clutch, if the rollers do not evenly grip the 58T starter gear, they will dent the surface on the starter gear boss, or on the roller ramps. A low friction oil might make matters worse.
These dents mean the rollers do not wedge properly. The attached photos show dents. Note that this starter clutch was previously reground (by eye, with a Dremel, not recommended), which makes the dents stand out.

It seems that the Kawasaki engineers eventually addressed this weakness on later ZR models. The sprag clutch is replaced by a one-way bearing that distributes the stresses over a far wider area, drastically reducing plastic distortion of the bearing surfaces (ok, this is getting into tribology porn). The ZR7S starter clutch is on the left, the original kz650 part to the right of the images. The ring bearing surface for the 58T starter gear is a different diameter too.

The question is, can you swap it into a kz650?

The answer is yes, swaps right in. No modifications required.
The technique for laying the bike on some tyres and performing surgery via the oil pan/sump is covered elsewhere.

Button the bike back up with a Motobatt 10U for serious cranking amps (Halfords full synthetic motorbike JASC compliant oil).
Perfect starting.

Part details: KAWASAKI ZR7 ZR7S (H1-H5) ENGINE STARTER CLUTCH GEAR 1999-2004
This part was taken from a 2000 model. As far as we know it will fit all 1999-2004 models of faired and unfaired versions.

Will this fit a 1980 kz650 modell too?

The part numbers are identical across the three bikes, easy to cross check using an online fiche service like cmsnl.com

The three parts on my kz650c3 are 13253001, 131931012 (131931062), 120461032
www.cmsnl.com/kawasaki-kz650c3-custom-19...t/57022.html#results

for the 1980 kz650e1: 13253001, 131931012 (131931062), 120461032
www.cmsnl.com/kawasaki-kz650e1-ltd-1980-...odel15500/partslist/
www.cmsnl.com/kawasaki-kz650e1-ltd-1980-...t/57260.html#results

the 1980 kz650f1: 13253001, 131931012 (131931062), 120461032
www.cmsnl.com/kawasaki-kz650f1-1980-usa-...t/57314.html#results
www.cmsnl.com/kawasaki-kz650f1-1980-usa-...t/57298.html#results

plus a few needle rollers and washers.

Do you have an exact list of parts from the zr7s that I need to acuire? This thread has totaly given me new hope on the starter clutch front!

You really only need the clutch/starter gear assembly with the associated needle bearing and internal spacer.
The sprocket and rubbers are identical but I never see them sold separately.
Hopefully the attached diagrams make it clear what parts are swapped.

This is the kz650 clutch assembly with parts to be swapped highlighted:


These are the ZR750h1 parts that are used:

Sweet idea!

Tks

Kind of related. The ZR750 ZR-7 ZR-7S oil pump can be used in the KZ650/750 engine. It has a higher output. But probably not really need in most applications. maybe worth considering with an 810 piston kit or Turbo. ???

KZR topic --- zr7 motor in KZ750

From the topic. by turboguzzi: ... BTW, you can do the pump swap with motor in place: the three bolts that hold the pump are behind the the clutch basket and the pump drops down from bellow.

I did both the zr-7 starter clutch and the oil pump swap when I rebuild my engine.
If using the wider zr-7 oil pump, you should also use the zr-7 secondary shaft as it has a wider gear to accommodate the different drive gear position of the wider oil pump.
Take note that the zr-7 secondary shaft uses a thinner shim/washer on the starter clutch because of the wider oil pump gear. If you use the wrong one or in the wrong order, the starter clutch will not free wheel. ( I accidentally installed them in the wrong position and the starter clutch up locked solid the first time I torqued the shaft nut down.)
The zr-7 oil relief valve is needed if using the higher volume pump as well.

Scroll to the bottom of the page to read about the swap.
kzrider.com/forum/11-projects/602462-kz750e-resto-mod?start=40