New KZ650 Project

Fellers-

Picked this baby up last Feb, finally got some time to try and gett'r going this last couple weeks.   Engine is pretty worn, and no matter what I do, I just can't get (it) making any kind of power.  It's just (worn) out.  Clock says 54k on it, but it sat for years outside under a tarp, and the valves and cylinders have rusted and pitted.  Compression is low, and the valves are leaking.   Bottom end seems fine, but I will tear it down to the bones and rebuild everything.   I just love the looks of it, paint is crap, but those classic lines and spoked rims are just the nuts!   

Question(s) for all you smart folks, I've read and heard that the 650 and 750 share many parts, and or parts fit from one to the other.  I can seen the cases look the same, can the head from a 750 fit on a 650?  Cylinders, cranks, cams compatible?   There are more performance parts for the 750 than 650, so that's why I want to know.  

Thanks
577nitro

 

Looking forward to seeing what you do with her 

So far I've found a big bore kit to 700cc, but no joy on cams yet.  I think that the 750 cams are the same, Webcams kinda says something like that, but if someone could please chime in here before I waste some money buying the wrong thing...again.

I've looked hard for a gpz750 engine to slip in, but no joy on that as well.  

577nitro-

The bike looks to be a 1978 KZ650 B2 so the engine uses a regular link cam chain and early cam chain tensioner.

If you have purchased the 700 kit that alone will give a lot more performance back into the engine (higher compression forged units) as long as you address the cylinder head as well. Most times on high mileage 650's the valves need done (seats cleaned up, valve faces reground, seals renewed, performance valve springs if you intend to rev it past 7K)

Once you get the engine sealed up and some compression back in the motor its going to be night and day. Hot compression needs to be 160-180 PSI to run correctly.

The 650 and 750 cams are the same at around .300" lift until you get into the later GPZ750 cams (the 83 and up version with no tach drive) which have .340" lift. Realistically if its a street bike just stay with the stock cams, more performance can be gained with a carb upgrade.

I suggest getting rid of the points (if it has any) ignition and upgrade to a Dyna system or OEM electronic system.

 

I've seen threads where 650 guys use a 750 cylinder and pistons.  Going that route would be a lot cheaper than a 700 big bore kit.  Maybe the head will fit too?  As mentioned, the cam chain on the 650 is the older type, so you need the old cam chain sprockets.  Too bad the old 650 site closed down.  That place was a treasure trove of info about that family of bikes.

Thanks for the info, great stuff.   From what I read in some of the threads as well,  the late model 650 uses the exact same case as the 750, and the 750 cylinders bolt right up.  Mine, is too old, and the case has to be modified to accept the 750 cylinders.   WebCams offers cams for kz750 and I think those will bolt up if they have the chain link style cam chain, you should be able to just swap sprockets off the 650 cams and put them on the 750 cams....I think in theory. 

No matter what direction I go I'm going to have to tear down an engine and rebuild it, whether its a 750 swap out, or the current engine that's in it now.  I defiantly want to bump the performance up to get back the loss from being at 6000' in CO.   A 750 build is pretty straight forward, lots of parts out here for it, 650 not so many.   If anybody has some ideas where to get performance goodies for the 650 engine that would be great.  

Thanks again.
577nitro-

The best way to get more performance is with cubic inches.

If you could find a early 750 barrel and bore it to 810 that is the best bang for the buck. Its hard to find NOS piston and cam kits for the 650 but its possible with a LOT of waiting/searching. You can buy APE performance valve springs off the shelf. Carbs are easy to get but cost a lot, CR29 is a good option that increases HP. The cam sprockets from the earlier motor fit the later cams and the other way around.

The other way would be to swap in a complete 750 engine, either a later (post 82) GPZ750 or the more modern Zephyr or ZR7 engines (it has all been done) they all fit the stock 650 frame but you need to make engine mount spacers.

I went with a Spectre engine as it was a lot cheaper solution for me, but a lot more work converting to chain drive. In stock form its just a couple of HP under the GPZ750 of the same year and usually a lot less money than the GPZ.


 

Nessism wrote:

Too bad the old 650 site closed down.  That place was a treasure trove of info about that family of bikes.

There is another 650 site,  Home | Kawasaki Z650 and KZ650 Forum (proboards.com)

Lots of 650 owners from the old site at the new site.


Looking forward to your 650 build 577nitro.

My 650 I've had since High School:

Injected wrote:

The best way to get more performance is with cubic inches.

If you could find a early 750 barrel and bore it to 810 that is the best bang for the buck. Its hard to find NOS piston and cam kits for the 650 but its possible with a LOT of waiting/searching. You can buy APE performance valve springs off the shelf. Carbs are easy to get but cost a lot, CR29 is a good option that increases HP. The cam sprockets from the earlier motor fit the later cams and the other way around.

The other way would be to swap in a complete 750 engine, either a later (post 82) GPZ750 or the more modern Zephyr or ZR7 engines (it has all been done) they all fit the stock 650 frame but you need to make engine mount spacers.

I went with a Spectre engine as it was a lot cheaper solution for me, but a lot more work converting to chain drive. In stock form its just a couple of HP under the GPZ750 of the same year and usually a lot less money than the GPZ.

 

Awesome bike I've looked at those engines, what does it take to convert over to chain?

577nitro-
 

rstnick wrote:

Nessism wrote:

Too bad the old 650 site closed down.  That place was a treasure trove of info about that family of bikes.

There is another 650 site,  Home | Kawasaki Z650 and KZ650 Forum (proboards.com)

Lots of 650 owners from the old site at the new site.


Looking forward to your 650 build 577nitro.

My 650 I've had since High School:

Sweet ride,  I'm sure you and that bike are one.   I've owned a RZ350 for 35 years, part of the family now.

577nitro-

 

577nitro wrote:

Injected wrote:

The best way to get more performance is with cubic inches.

If you could find a early 750 barrel and bore it to 810 that is the best bang for the buck. Its hard to find NOS piston and cam kits for the 650 but its possible with a LOT of waiting/searching. You can buy APE performance valve springs off the shelf. Carbs are easy to get but cost a lot, CR29 is a good option that increases HP. The cam sprockets from the earlier motor fit the later cams and the other way around.

The other way would be to swap in a complete 750 engine, either a later (post 82) GPZ750 or the more modern Zephyr or ZR7 engines (it has all been done) they all fit the stock 650 frame but you need to make engine mount spacers.

I went with a Spectre engine as it was a lot cheaper solution for me, but a lot more work converting to chain drive. In stock form its just a couple of HP under the GPZ750 of the same year and usually a lot less money than the GPZ.

 

Awesome bike I've looked at those engines, what does it take to convert over to chain?

577nitro-





 

To do that conversion you can split the cases without removing the barrels if needed, just invert the engine and work from the oil pan side. Take off the shaft cover and shaft housing first before splitting the engine. You have to remove the 750 transmission because the gear ratio is weird compared to a chain drive bike. I took the complete trans out of a 650 and it fits with no issues, the 650 and 750 clutch are identical. There is a oil feed hole that went into the shaft drive housing, it needs to be plugged with a 1/8 NPT fitting, it is next to the clutch rod. You can use any clutch actuator cover but I chose to use one from a KZ700 as it has the better release mechanism. You also need to make a custom gasket to allow the use of a 650/750 trans door cover, a stock gasket does not cover enough of the machined surface (the shaft housing gasket surface is slightly larger than chain drive trans cover) You also have to make spacers at every engine mounting point if going into a 650 frame as these newer engines are all rubber mounted, I made mine from 1" OD 6061. The front sprocket lines up with a thin shim behind the sprocket (.050-.060") so chain line is not an issue.

The engine is out of a 1982 Spectre, it had been stored for a lot of years so I put new rings in it. In that picture I am using CVK 34 mm carbs from a 1990 Ninja 750 I re spaced, that is the only performance upgrade except for a Dyna S and green coils. The exhaust is stock 650 F model, the air box has been modified to take the larger CV inlet rubbers.
 

Well feller's, after much gnashing of teeth, I decided on a course of action for the 650.   Because I like the aesthetics of the 650 engine, I'm going to do the big bore kit to 700cc and 10.25CR (I still would have had to OH a 750) .   Also will send the head off to be overhauled and maybe have the larger 750 valves installed.   At the same time I will send the cams in to WebCams and have them regrind with the mild race/hot street.  Might have the head skimmed to get some more compression to overcome the 6000' to 8000' altitude CR loss (21%).    

Rest of the (complete frame off) restoration yet to be determined, but thinking the OEM Emerald Candy Green (even have a spare tank and bits for this already), dual front disk, RaceTek Emulators and springs in the stock forks, KYB rear shocks re-valved by DMR, fork brace, (maybe) re-lace with Alu and wider rims to fit a 130 to 140 rear 110 front,  carbs undecided: maybe stock using the stock airbox and K&N filter...or set of 26 to 29mm CR's, steering dampener and a oil cooler.   

I'm building this as a rider, commuter, tourer and something the wife can ride with the lower seat height.   I figure I'm going to be at least $8000.00 richer compared to the price of a new Z650RS.   With a purchase price of $500.00 you can't go wrong!  I think this is going to be a pretty dang fun little bike.   

577nitro-