Whelp! I found the problem.

As luck would have it, I think I found not just one, but two ZX600A engines for sale near me. Same seller. I’m planning on going to go take a look at them on Tuesday. 

Is there any particular things I should be looking for? I figure if I can come to a good price with the seller, I want to get both motors, a radiator, and as many of the cooling hoses as I can find. If I can spot a set of carbs, I’ll grab those too. But should I look out for anything else? 

Im pretty sure the gpz600 oil cooler bolts up differently compared to your Zephyr 550 oil cooler so they won't interchange.

When I got my gpz550 I seriously considered doing this swap since there was an engine near me but decided to keep it "original". It looks like a lot of fun! I'll be following along.
 

Engine wiring and the ignition system if different from yours. What are your plans for the exhaust? You may want to grab the headers at least?

Upon further inspection of the sale listing, it looks like they have a whole at-least-mostly complete bike, plus the spare motor. There’s other loose parts I wouldn’t want, but it seems like there’s a good chance I’ll be able to get everything I’ll need. I’m getting kind of excited about this. It’s got me fantasizing about getting an AS Uotani SPII ignition for it. I’d make custom side decals that say “Zephyr 600R.” 

That's exciting! It gets me wondering, now that you mentioned ignition, how are you going to deal with the ignition pickup coils? I had an issue with that once with a kz550 and zx550 engine (mechanical advancer vs electric) for incompatibility of  things such as the igniter, since it doesnt look like they will be plug and play. Your Zephyr only has one pickup coil and the gpz600 has two!! Just my thoughts for you to consider.

Incorrect, my Zephyr has two. 

Whoops, mildly embarrassing. I was looking at diagrams, thus my mistake. The diagram didn't show the other coil. I'll try to be more careful! 

The ignition box that goes with the motors is probably the most important ancillary you will need. It will be engine specific to the zx600 pickup-coils, and reluctor wheel in order to deliver the correct timing map. 
All the coolant pipes and the fill tube/cap would be very useful to have, but can be custom made to fit the bike. 
The oil cooler ports are banjo style on the oil pan, so those hard lines would also be helpful, but can be custom made to fit your zr550 cooler as it will have to be custom fitted to share space with the coolant radiator. But I distinctly remember the guys in the UK used specific oil pans that did not have oil cooler ports from the factory and they deleted the oil cooler entirely. 
The 600 exhaust header diameter and spacing is identical to any kz/gpz/zr550, so you might to be able to use your entire zr550 exhaust. 
Carbs for the 600 will be cvk32’s and the zr550 uses cvk30’s. The 30’s would probably work just fine (and add torque) until 32’s can be sourced. They also use the same style throttle cables, but the lengths may be different. 

 

Went up to check out the bike and parts for sale this afternoon. The bad news is that everything was in pretty rough shape, and I didn’t get as much as I was hoping I’d be able to. The good news is I did leave with a motor and a few other parts for a lot less money than I thought I might spend. 

It does feel a little bit like getting this motor to work is going to take just as much or maybe more effort than repairing my original motor. But what I can do now is work on both of them in tandem, and at some point make a decision about which one is actually going to get put in. First things first, the ZX600 motor needs a bath real bad. It’s too dark here now to take a picture, but I’ll try to remember to get one in the morning. 

Here’s a photo. It gross. 



I got a radiator, oil cooler, and a handful of additional hoses as well. 

Oh man….
I am really excited about your project. I can’t tell you how long I’ve wanted to see somebody try this swap and actually document it. 
If I didn’t live half way across the country from you, I would love to volunteer my time and lend a hand. But I can help research and problem solve if that helps any. 

 

Stereordinary wrote:

Here’s a photo. It gross. 

I got a radiator, oil cooler, and a handful of additional hoses as well. 

did you get the ignition module and the wiring harness (easiest way to get the plug for the igniter, pick up coils etc - for my project I got a ZX6R loom for the dash, speed sensor etc and a GPX600 loom for the ignition module etc. I paid around $40 for each)