650/750 swap

Hey Guys, I've been gone for quite some time, Been working on my other bike, a Honda CX500, riding, semi working on, then a mowed down a deer doing 50MPH, walked away with only road rash and... surprisingly, the bike pretty much laid down and slid (it didnt roll or go flipping) so damage was much less that you'd expect for a deer/motorcycle collision.

Anyway, geez, first post and im already off topic?

So there is a 1982 KZ750 for sale for cheap (no title, will run after carb clean (Guy bought a storage unit and, that was inside)) so naturally, the idea of a Kz650/750 hybrid has gone through my head. Now I've seen a ton of other people posting threads concerning the same thing, so why dont I start with what i have/know and that'll help ask my question.

What I have/know:
1979 KZ650 B3

Has standard cam chain and the 82 has HyVo and i'll have to swap the sprockets on the 750 cams to retain the timing chain. I'll also have to remove material from the bottom case so the 750 jugs will fit into the 650 bottom end. So from what I understand is, I'll need the 750 pistons, jugs, cyl head and cams with 650 cam sprockets.

What I'd like to know is, will the oil galleries line up? Also... is there even any advantage to doing this swap? Do I gain anything really from doing this?

Why not just swap the engines?

Yes-swap the engines complete!

I would Keep the z650 ignition IC box, coils, ATU timing rotor and charging parts. I'm assuming this is transistorised igntion? Use the z750 timing plate and maybe pick up coils too -the slots and mount points can be in different positions between early and later crankcase castings on some models, even though they look the same.. I had to elongate the ignition timing plate slots to get my timing back on a 550 old/newer engine swap. Take care when timing it for this reason, even if it looks right., and use a strobe to check.

Check you have a 3 phase alternator on the z650, (three yellow wires coming from stator) otherwise if an early 2 phase you need to fix this by changing the stator , maybe the regulator rectifier box and probably the rotor I guess.

Engine swap is easier with the cam cover casing taken off, also it is a good opportunity to check the valve clearances. You might need to do something if your z650 tacho is cable driven, the later 750 may be electronic without a drive gear on the camshaft, and the cylinder head casting won't have the tacho drive gear hole. I need to do just this on a GPz550D1 project, there's ways of doing this

The 650s thru 1980 had points ignition. The 750 has electronic ignition; he'll either have to find an igniter or make one.

For the 750 charging system, if he can't use the 650 voltage regulator, he could get one from a Ninja 500 or Vulcan 500 up to 2009 (credit to loudhvx).

...or swap just the block and pistons, keeping everything else from the 650, assuming the 750 parts are within spec.

A friend of mine did just this - not sure about the details but the result was a nice smooth motor with plenty of low end tourque. I't was't arm wrenching fast, my 81 gpz550 had the edge on it, but it was fun to ride. Going from up 652 cc to 738cc on it's own won't make a big difference imo.

Since I have done the 750 swap on mine
let me say a few thing's about doing it.

1. You CAN NOT swap the later hyvo top end
on to the early roller motor. Use complete 750 motor.
2. Use the complete Ign. system from the later motor
and you will need to have the clutch/side stand switch's or just
ground that wire to bypass.
3. use the stater from the early motor and no rewiring needed
4. Use the VM carb's from the 650 motor and the stock air box will still work.
5. On the later 750 motor's some of the mounting boss's are narrower
so some spacer's and new hardware will be needed.

Tyrell Corp wrote: . Going from up 652 cc to 738cc on it's own won't make a big difference imo.

A 10% increase in displacement will give you a 10% increase in torque, with no other changes.

What's the torque rating on a 650? 30 lbs ft maybe? If so, then 10% of 30 is 3, so not a big difference. But if you use the 750 head and cams, then it's more. Add a little compression, get a little more, and pretty soon you're talking serious money :lol: :lol: