Z550 Cylinders, pistons and head on Z400J bottom end?

Hey guys, some of you may have seen my other post about my Z400J that is currently a semi rolling frame and an engine what was seize. The previous owner left one spark plug out which ruined the whole thing, the cylinder is now damaged and very pitted. I tried cleaning it up with a hone but feel it it has gone too far. 

Anywhooooo...My question is......would it be possible to place z550 cylinders with the pistons and maybe rods if needed along with the 550 cylinder head onto the Z400J bottom end? I can find loads of 550 parts and I believe the frame is the same. Id like to keep her as a 400 but pricing it up and cylinders would need oversizing and honing machine work which id imagine is costly. 

Any thoughts ?

The 400 has 52mm bores and the 550 has 58mm bores - not sure if there would be enough meat in the top crankcase to bore it that far for the bigger liners (how wide is the bridge between cylinders currently ?)

I have just been out and the top of the crankcase is 66mm. I have included a picture also. 
 

The important part is the bridge between the cylinders ( the measurement I gave you was the bore size so you need to add the thickness of the liners to that) it also looks like you would be close to the oil passage on the right even at 3mm added to the radius (assuming the 550 liners are the same thickness as the 400 ones

so are you saying it could work but it would be close or it wouldn't work ? I have no idea how thick the lines are on a 550 to check as I don't have a set 

MrGMoto wrote:

so are you saying it could work but it would be close or it wouldn't work ? I have no idea how thick the lines are on a 550 to check as I don't have a set 

What I'm saying is it looks marginal as far as physically being able to bolt it together, as far as what cam chain to use, con rod length, piston pin location etc not to mention whether or not the crank and transmission could cope with close to a 40% increase in capacity are all unknowns. Maybe if you search the Internet long enough you may find someone that has done it already. If not you will be venturing into unknown territory. Good luck with whichever route you choose 

I appreciate your honesty, I didn't realise they have 40% increase compared to he 400. if it were you , would you rebuild the bike and put a 550 engine in it for rebuild the frame etc or rebuild the 400 in with oversized pistons obviouse requiring bore and hone to accept the new oversize? 
 

I guess you need to decide what you want and what your budget is. 550 swop looks attractive but don't forget you will be buying  a 40 year old engine with unknown history so it's a lottery (smaller engines tend to have been thrashed mercilessly) also in the UK depending on your age an engine swop will bring insurance issues. The smart move would be to rebuild the 400 (if you can find oversized pistons- I had a quick look and didn't find any) with new crank bearings, oil seals and a head refurb you will have a solid dependable motor you can enjoy for years
PS: 550-400= 150/400 = 37% (sneaks up on you doesn't it  )

Crankshaft web/con-rod/piston ballance would be wildly off!

The 550's piston wieight would not be "ballanced" by the 400's crankshaft webs, and, in my opinion, main bearings would fail pre-maturely.

H.
 

The KZ400J stroke is the NO GO argument!

 
 
 

The 400/550 hybrid has been done before to produce a perky 500 motor.
There was a feature on it in either Performance bikes or Superbike mag in the late 80's early 90's and i had a 400J at the time which is why i remember .
I don't recall the finer details of which carbs and cams etc were used but the main mod was either milling the 550 block down to suit the 400's shorter stroke or boring the 400 block to take the 550 liners.
Essentially you get a big bore using factory parts, the 4cyl crank is self balancing so no issues there and the rest of the 400 motor is up to the job.
The 500/550's are just a bored and stroked 400 and the whole engines are physically a straight swap.
 

Thanks for the info! got a question, I can only track down 3 oversized pistons. would it be possible to use 3 over size and 1 standard ? or would this unbalance everything ?