1990 Zephyr 550 Project

I have a used KZ550AE engine that has good compression, seller said it came off of a running bike.  I picked it up in the dark and now that I have it in my garage and I am getting a good look at it, it will not bolt into the frame without modification.  The clutch cover is different, oil fill is in a different location and there is no clutch arm.  The sprocket cover has the clutch cable, rod, etc which wouldn't work with my frame because the Zephyr 550's is cut to fit the frame.  The output shaft is shorter on the KZ550AE which is another problem.  I was hoping to just bolt this thing in and go.  

Will the KZ550AE crank fit the Zephyr 550 engine case?

Hello. While the KZ engine looks different from the ZR's on the outside, they're pretty much the same internally. The crankshaft is identical, and the gearbox is the same, apart from a few modifications on the ZR. The output shaft is longer because the wheel is wider on the ZR, by 10mm. The ZR camshafts are better than the KZ's. I'll say it again, a ZR is basically a slightly less powerful KZ550H. It has lower compression and a terrible exhaust. The most powerful is the ZX550, the best is the KZ550H, and the worst is the ZR. 😄

all 550 crankshafts are compatible with each other

The ZR engine is closer to the ZX than the KZ. It uses a lever clutch instead of a rod clutch, and the ZR engine covers fit the KZ and ZX engine blocks. With some work and parts swapping between the two engines, it's possible to rebuild a ZR engine using a KZ engine.

My avatar motorcycle was originally a 400. By changing a few parts, I converted it to a 550. I'm working on a cylinder block to increase it to 615cc, with a camshaft and cylinder head from a ZX550, a GPX600 gearbox with a short output shaft, and GPX600 carburetors. ZX ignition. ZR7 fuel pump. You can do just about anything with these engines.

 

Fellow Zephyr 550 owner here. 
After doing a restoration on my bike, I found out how hard it was to find spares for these as they sold them for such a short time in the states. I have since purchased two parts bikes, so I have a spare motor in the shed with only 3000 miles on it. That being said…..if I ever blow up the motor that’s currently in the bike, I will almost surely swap in the motor from a 1985~1997 zx600a/b/c “ninja”. 
They are know to bolt into a zr550 frame with some custom spacers and such. (If I remember, nothing gets welded or changed on the frame mounts) They have more power, easy to adjust valves, any 4-1 exhaust header and possibly entire exhaust from a zr/kz/gpz will bolt right on, they have a primary chain tensioner, the exact same length output shaft, and even the zr550 cvk30 carbs will bolt right up with no modifications. (Original zx600’s had cvk32’s but the 30’s will still work) And I noticed folks are selling old zx600r’s for next to nothing as nobody collects them yet. In the long run it might be cheaper to buy a donor bike than doing a complete tear down and rebuild of the 550. 
The main issue is the motor is water cooled, so you have to be clever in mounting the radiator and associated plumbing. 
Before the Zephyr-Zone went tits up, there were a couple of guys who had done the swap and posted about them. I saved the pictures, but didn’t think to take screenshots of all the dialog of how they did it. 
If this is something you might have interest in exploring, I can try and find those photos that are somewhere in my desktop computer. 

Something to think about…..

Bloobaba wrote:

Hello. While the KZ engine looks different from the ZR's on the outside, they're pretty much the same internally. The crankshaft is identical, and the gearbox is the same, apart from a few modifications on the ZR. The output shaft is longer because the wheel is wider on the ZR, by 10mm. The ZR camshafts are better than the KZ's. I'll say it again, a ZR is basically a slightly less powerful KZ550H. It has lower compression and a terrible exhaust. The most powerful is the ZX550, the best is the KZ550H, and the worst is the ZR. 😄

all 550 crankshafts are compatible with each other
 

Thanks for that valuable information.  It's great to know I can use the crankshaft.  I'd agree that the ZR is the worst at this point in time but I may be a little biased. Ha, ha.  It looks like I will be taking two engines apart in the near future, probably after Christmas and New Years.  


 

This is very interesting information that I was not aware of, and would love to learn more. Could you try finding those photos and maybe post up a separate thread with them and any other information you remember?