TOPIC:

I’ve been thinking that I may someday want to get the Wiseco big bore kit that would punch my ZR550 out to 615cc, but I have to admit that there are some things about it that mystify me. I’m hoping you all can shed some light on it. 

I suppose my big question is about longevity. Does the bigger displacement produce more heat and wear and tear on  the motor and is it a mod that shortens the life of the bike? Or is that not a problem? 

I gather that the engine has to be bored out and that’s no small job, but something that should be done by a reputable shop. So does anyone know a good shop in the Portland area? Or can Wiseco provide the service? Same with the dyno testing, how do I know the shop I take it to knows what they’re doing? 

I guess maybe I’m just nervous about the idea. On the one hand it sounds like the best option for really getting maximum performance out of my bike. But I don’t want to risk ruining what’s already a good thing. Help? 

Done correctly the increase will not have any adverse affects on longevity or reliability.

 

Thanks for that. Are there any other considerations I should be thinking about? Will the carbs need to be re-jetted? 

It's not much of an increase per cylinder and all you may have to do is go up a size on the main.
If the increase in bore size is within stock oversizes and compression you wouldn't need to rejet but if you have an increase in compression then you will.
Always start a few sizes larger and work down.

I have a friend offering to sell me his unused Wiseco big bore kit and an already bored and sleeved cylinder block, and I just want to make sure it will fit my bike before I buy it. We're both pretty sure it will, but just for peace of mind, here are the details.

Here's the kit: www.svspowersports.com/products/wiseco-top-end-rebuild-kit-k615

And the bored and sleeved cylinder block is from an '81 GPZ550.
 

If anyone knows for sure that both will fit, I'll get both. But if the cylinder block doesn't fit that's ok, I would still pick up just the Wiseco kit.

One bit of good news is that both the base gasket and head gasket are the same between your bike and the early 550.  Also, the cam chain tensioner shoes seem to be the same as well, although the tensioner assembly itself is different.  You may need to get an early tensioner.  Overall, it seems likely that you can make those parts work with your bike.

I bought it. 

 

I got the kit installed. Still waiting on some things before I can fire it up, but I’m looking forward to it. 

 

The bike is all put back together, and running! I haven’t actually taken it out on the road yet though, because the idle sounds rough. To my ear it sounds like probably a loose cam chain but I’m wondering (and maybe a little concerned) that it could be something else. 

Here’s a short video, I’d love if anyone can listen closely and help me diagnose it. 

I was going to say that I've heard that forged pistons tend to knock more when they are cold due to larger piston/bore clearance than cast pistons, but googling that idea a bit seems to suggest that it isn't likely to be true?  I don't know.  It sounds like that's probably not the source of the noise.  On the other hand, my bone stock KZ650 used to knock at idle in a way that didn't sound great.

If seems like you bought the cylinder block already machined?  Did you measure each cylinder bore and piston diameter to make sure they were sized and matched correctly?  Were the pistons numbered/marked to show they were matched with a specific cylinder?

As a zr550 owner, something is not right! 
When I bought bought my basket case zr550, it had suffered from a cam chain that was run so loose, it wore grooves in the cam chain tunnel of the cylinder block, yet it sounded nothing like this. 
But as mentioned, you should have sourced a kz/gpz style cam chain tensioner as I’m almost sure they are physically different than the Zephyr one. I replaced my auto tensioner with a manual version as the auto tensioner failed and  was the reason behind my loose cam chain. 
You need to get a thermal temp gun/device to measure and compare the exhaust pipe temps between cylinders. It 100% sounds like you are running on 3 cylinders. That will cause the terrible primary chain/clutch basket slap that sounds a lot like what you have there. 
Also if the carbs have not been synced, it will cause terrible clatter like that. 
But If you are indeed running on all 4 cylinders and they are all jetted and synced properly (again the header temps will tell you that) then as mentioned, there was something seriously done incorrectly in the machining process.
Yes, billet pistons vs cast will have a small difference in clearances as specified by Wiseco, but nothing that would cause that clatter. 
Also….you mentioned that the cylinder bores have been “bored and sleeved”. 
Stock sleeves do not have to be replaced to bore it out to 615.
 And seeing that the cylinder block in the pictures does not appeared to be decked, if they did re-sleeve the block for whatever reason, they 100% should have decked the surface to ensure the sleeves are perfectly flush. Or…if the sleeve was installed and was not fully pressed down to the lip, that sleeve could be loose in the bore and causing that racket. 
(I am not a machinist by trade, but I work at a race engine shop and am aware of good practices.) 

Food for thought

my 750 sounded like that - like an old farm tractor , and really really loud - when the locknut on my manual cc tensioner loosened and the adjusting bolt backed out almost all the way.

or yeah. Maybe running on 2 or 3 cylinders