The story goes, the bike was bought about a year ago and apart from tired and worn suspension it seemed pretty good, so a gsxr600 k6 rear shock was fitted and the forks were re-valved by perry leask at hm racing and after perry had set it up it handled like nothing i'd ever riden before! things were going great for a while untill a just before christmas on a ride out it started running on 3. I pulled over and while i was trying to figure out what was up the engine stopped dead and a peice of aluminium shot out from the fairing just missing my head!
After it got trailored home it was stripped down and we could see the end of a broken rod trying to make an exit underneath the carbs
While i was deciding what to do a zzr600 came along nice and cheap, it'd been laid up for a few years but it was all there. Proper nasty paint job though!
So both bikes were stripped down and the 600 lump was offered in the the chassis to see if it could be done. It was instantly obvious that 3 out of the 4 engine mount "lugs" would have to be cut from the frame and new ones welded in, but it looked possible so we cracked on!
The engine was blocked up in position and everything seemed to line up ok, the chain line was 6mm out but this could be corrected by either having a special offset front sprocket or machining 6mm from the face of the cush drive. The exhaust headers from the 600 fit but would need minor modification to meet the silencer. The only real problem seemed to be the radiator, the 600 engine was longer and sat further forward so between the exhaust headers and the front wheel was barely enough room for the rad.
After much experimentation it was decided to use the 600 rad (albeit with the fan removed), which strangely was smaller than the 400.
The 400 engine has a boss either side on the back of the head which is bolted to a steel plate in turn bolted to the frame, the 600 had a boss with a rubber mount inside it on the front of the barrels much lower down. It was decided that we'd make a steel bracket that attached to the engine using the outside 4 head bolts which would bolt to the original holes on the front of the frame. The washers under the head bolts were 2mm thick, we removed those and made the bracket from 3mm thick steel sheet- so only 1mm of fixing was lost.
At this point we decided that the whole swap was possible.
So new 3 new engine mounts were made from 10mm aluminium plate and a pair of head steady mounts made from 3mm thick steel sheet with hollow box section arms to mount the rad too. The original zzr oil cooler bracket was modified to fit and all was looking good.
I do all the sleel fabrication myself but for alloy welding i got to alph welding in croyden, so with everything in place it was down to Alec.
Then it was fitted back together for hopefully the last time, engine in, rad and oil cooler mounted, throttle cable and clutch cable fitted straight on! The gear linkage didn't fit but by cutting the bracket and moving it over 1/2 inch it went straight on
Because the rear engine mounts had moved, the access holes in the frame didn't line up and it was impossible to get the bolt in. I didn't want to drill another hole in the frame so i decided to remove the webbing in between the mounts on the engine and use 2 bolts to secure it instead
That's it so far, so next is to connect coolant hoses, wiring loom, i think the base of the tank will have to be modified to fit over the bigger air box, exhaust, modify fairing to fit around the re-positioned generator cover
I'll keep you posted,
, I love seeing something a bit different. Should be an awesome sleeper bike. 
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