TOPIC:

I’m prepping for a wiseco 615 engine build for my zr550.  cylinder heads are few and far between. I’m thinking about buying a zr400 cylinder head from japan (there are many used ones available). Anybody know if I can bore the 400 jugs to 615cc without having to replace the sleeves? My understanding is that the zr400/zr550 engines are almost identical, other than the pistons and crankshaft. 

I think that the Zephyr400 used smaller sleeves to keep the wall thickness as such it would dissipate heat properly. So I believe that to bore them to 550 or 615, the sleeves are removed, the block bored and the 550 sleeves are installed. 
There is a zr550 cyl block on eBay right now, that might work. 

Here is a Japanese blog/post that I think illustrates the 400 to 550 process. (Google translate will help) 
erkkiyonaga.blog62.fc2.com/blog-entry-138.html

Does this answer your question?

 

Haha, just kidding. 

But I am curious why you would need another jug, instead of just using the one that’s already in your bike? 

By the way, nice to see you both. 

wrote:

I think that the Zephyr400 used smaller sleeves to keep the wall thickness as such it would dissipate heat properly. So I believe that to bore them to 550 or 615, the sleeves are removed, the block bored and the 550 sleeves are installed. 
There is a zr550 cyl block on eBay right now, that might work. 

Here is a Japanese blog/post that I think illustrates the 400 to 550 process. (Google translate will help) 
erkkiyonaga.blog62.fc2.com/blog-entry-138.html



 

Ah. I think you’re right. Good to know, and good Japanese website sleuthing. Thanks!

wrote:

Does this answer your question?

 

Haha, just kidding. 

But I am curious why you would need another jug, instead of just using the one that’s already in your bike? 

That’s a sweet bike. 
I’m planning to build the engine over time and want to keep riding while I’m doing it, hence ordering extra parts rather than modifying my current head.

Ah, makes sense. Figured that had to be why. 

I wanna do the same thing, but instead of a jug I want to find a whole bike, lol. 

wrote:

Ah, makes sense. Figured that had to be why. 

I wanna do the same thing, but instead of a jug I want to find a whole bike, lol. 
 

I actually did that - bought a parts bike thinking I would modify that engine, but the bike is in such good shape (only 10K miles and unmolested) I think I'll just keep it stock as a spare. 

 

Nice! I'd probably do the same thing. My current (one and only) bike (550 Zephyr) is mostly original, but after the accident I was in last year it's now a rebuilt title, so I kind of feel free to modify it tastefully as I see fit. So if I can get another bike to ride while doing the big bore kit I won't hesitate. 

I also found that getting spares for a zr550 was really difficult, so I bought a parts bike and upgraded my kz750 with some of it and tidied up my zr550 with the rest. I also ended up with a complete motor that only has a little over 3,000 miles on it. My spare bike parts take up more room than my actual bikes.