That's a US only model produced for only 2 years 86/87. (This means when spares are required for that then they may be scarce)
Not available in UK...we got a 750...the full power version (+ 10bhp) It was not that popular.
Anyhow : you have the item infront of you.
I doubt anyone has done the swap previous....It's a bit retrograde for a sportsbike.
Certainly the electrics will require swapping/modification and I doubt the airbox that goes with the 700 carbs will fit ...then that leaves the tank and cover to modify.
Shame to strip a working bike to fix an engine fault on another.
Personally I would source a good used engine for your Fzr.
Cost of rebuild components for your original make the repair economically unviable.
It's a barrels off and crankcase split job.
Genuine gaskets aren't cheap (head /base)...Athena kit may suffice for others...a new camchain would be fitted when split.
It is normally the engagement dogs that are damaged on 2nd gear failures...they can be undercut and reused but new replacements are more viable (time/cost factor)..If you do this then certainly replace a worn fork if found.
I would replace the dedent assy and gear selector with an upgraded version once this amount of time/ money has been spent
You now will begin to understand why these engines are replaced by another complete 600 unit by 95% of owners.
Lots of Fzr 600 units are still run with the failed 2nd gear...short shifting and using the upper gears gets as much performance as required for many riders. Every take off does not have to be a traffic light G.P.
