KZ650 to 750 Conversion - Cylinder Block & Pistons

My 1982 KZ650 still runs OK, but the compression has gradually gotten lower, along with the power level, and I am using more oil. I borrowed a fiber optic device that I was able to insert down through the spark plug holes and look at the cylinder walls. There was significant pitting of the walls. You could see where the piston rings must have remained for many years, perhaps with moisture in them, just corroding away. One place looked like a small piece of the cylinder wall had been jerked out. I expect the engine was "stuck" and then broken loose, etc.

Anyway, I don't want to spend a fortune on it, but would like to get it running better. If I can find a good one, I am considering buying a good cylinder block, of course with sleeves, plus pistons with rings and pins from the same engine. Then installing those parts within my 650. I have read that this can be done, but have many questions:
1. Provided I get compatible year models, will the 750 (actually 738 cc) cylinders fit into the 650 lower case?
2. Can the 650 cylinder head be used?
3. I expect the combustion chamber volume may be less on the 650, and cause a rise in compression ratio. (I wouldn't mind some increase). Is this a concern?
Perhaps the 750 pistons have less deck height or something to compensate.
4. Will there be any valve to piston interference?
5. Will the small ends of the 650 connecting rods fit the 750 piston pins?
6. Presuming the 750 pistons may be slightly heavier, will there be any out-of-balance concerns?
7. Does anybody happen to know what years I should look for? Some cylinder assemblies appear to have circular bosses that support the cam chain rollers, and some do not.
8. I have read where my bike was referred to as a 1982 H2 model designation. My engine number has KZ650DExxxxxx on it. How do I tell what I have?
Thanks everybody for the input.

The cylinders will not fit in the 650 cases. You need to bore out the upper case. If this is not something you're prepared to do the rest is a moot point. Theres a sticky over on kz650.info which covers this.

Cheapest route would be good used cylinders and pistons from a Kz650.
Next cheapest would be the K700 kit from Wiseco: wiseco.com/ProductDetail.aspx?ItemID=K70...Year=1979&AppID=6895

T_Dub is correct, the upper case will need to be bored to accept the larger O.D. sleeves for the Kz750 whether you are trying to put them in the Kz650 jugs (will require boring, not sure if it makes sense to do so), or are using the Kz750 jugs.

There is a ton of room in the combustion chamber - you shouldn't have any piston to valve clearance issues unless other modifications have already been made.

With the exception of the Gpz750 turbo:
650 and 750 small ends are the same.
650 and 750 rods are the same.

Balance is an issue in a piston set. The 750 pistons should be close to the same weight as each other.

Most of the Kz750 line has bosses you are looking for. I have an 82 Kz750E that has them.

Model designations can be found on Kz650.info: models.kz650.info/Models.php

Best bang for the buck just find a 750 motor.

I was going to do 750 liner's in my 650 block with an
810 kit till the deal on my GPz750 motor.
About the same power as the hot rodded 650
would have and cost me $100 for the whole bike.

Get one around the year of your 650 and it should
be a plug and play swap.

I think you are wrong about having to bore the case. The motor he has already has the HyVo style cam chain, and I think it's actually a 750 motor with smaller bore. It doesn't even have a kick starter.

I just checked kawasaki.com parts diagrams and it says the cases for the 82 KZ650 are also used on the following models:

Model (5):
KZ650-H2 (CSR) (1982)
KZ650-H3 (CSR) (1983)
KZ750-H2 (LTD) (1981)
KZ750-H3 (LTD) (1982)
KZ750-H4 (LTD) (1983)'

Also took a look at the cylinder base gasket, and all the following models use the same gasket.

Model (26):
KZ650-H1 (CSR) (1981)
KZ650-H2 (CSR) (1982)
KZ650-H3 (CSR) (1983)
KZ700-A1 (1984)
KZ750-E1 (1980)
KZ750-E2 (1981)
KZ750-E3 (1982)
KZ750-F1 (LTD Shaft) (1983)
KZ750-H1 (LTD) (1980)
KZ750-H2 (LTD) (1981)
KZ750-H3 (LTD) (1982)
KZ750-H4 (LTD) (1983)
KZ750-L3 (1983)
KZ750-N1 (Spectre) (1982)
KZ750-N2 (Spectre) (1983)
KZ750-R1 (GPz) (1982)
ZN700-A1 (LTD Shaft) (1984)
ZN700-A2 (LTD Shaft) (1985)
ZR750-C1 (Zephyr 750) (1991)
ZR750-C2 (Zephyr 750) (1992)
ZR750-C3 (Zephyr 750) (1993)
ZX750-A1 (GPz 750) (1983)
ZX750-A2 (GPz 750) (1984)
ZX750-A3 (GPz 750) (1985)
ZX750-E1 (GPz 750 Turbo) (1984)
ZX750-E2 (GPz 750 Turbo) (1985)

I think I'd be willing to bet money you don't have to bore the cases for the 750 cylinders, just bolt on and go.

Good to know - makes sense too.

T_Dub: After checking many parts diagrams, I believe what you say is true for the earlier models, regarding the sleeves fitting into the 650 case. Also, I believe Steell is correct for the later models, which mine is. Steell is correct about my cam chain, and no kick starter. Thanks zukdave for the idea about a GPz750 motor. Thanks Double Dub about the connecting rods and valve to piston clearance. Thanks for the KZ650.info advice. I hadn't been over there in ages.

I still wonder about the possible increase in compression ratio. I'm OK with this, if it doesn't go too high. If the combustion chamber volumes are porportional to the displacement, then: present CR = 9.5 x (738/652) = 10.75 I expect the 750 pistons lower this somewhat. Anybody have experience with this issue?

Regarding the possible out-of-balance - I presume the 750 pistons would weigh a little more than the 650s due to the larger diameter. Even though the crankshafts are the same part number, I imagine that the counterbalances are drilled a little to perfectly offset the weight of the piston, rod, etc. Perhaps the weight difference is inconsequential. Does anybody have experience with this?

One more question - Is it true that a KZ1000 engine will NOT fit in my 650 frame?

Thanks guys. Y'all are fantastic!

A KZ1000 engine can be put in the KZ650 frame, BUT the frame will need to be modified....

WABBMW wrote: Regarding the possible out-of-balance - I presume the 750 pistons would weigh a little more than the 650s due to the larger diameter. Even though the crankshafts are the same part number, I imagine that the counterbalances are drilled a little to perfectly offset the weight of the piston, rod, etc. Perhaps the weight difference is inconsequential. Does anybody have experience with this?

Really not following this. Are you saying that everyone who puts 1075cc, 1200cc, 1500cc kits in in their Z1/Kz900/Kz1000's are having balancing issues? I have never heard anyone complain.

Pretty sure the counterbalance holes are meant to balance the unit, not the entire assembly.

That is a sweet ride. Anymore info on it? Thanks.
Wayne

650ed wrote: A KZ1000 engine can be put in the KZ650 frame, BUT the frame will need to be modified....

DoubleDub:
Your comment about people going from 1000 to 1075, etc. puts things into perspective for me. The difference in piston weight must be of no consequence. Or perhaps the larger bore pistons have some other feature about them that keeps the weight about the same. At any rate, I ordered a head and pistons from a 750 that I plan to install into my 650. All I want is for the engine to have decent compression, performance and not use excessive oil.

I'll report back and let everyone know how it works out.

WABBMW wrote: T_Dub: After checking many parts diagrams, I believe what you say is true for the earlier models, regarding the sleeves fitting into the 650 case. Also, I believe Steell is correct for the later models, which mine is. Steell is correct about my cam chain, and no kick starter. Thanks zukdave for the idea about a GPz750 motor. Thanks Double Dub about the connecting rods and valve to piston clearance. Thanks for the KZ650.info advice. I hadn't been over there in ages.

I still wonder about the possible increase in compression ratio. I'm OK with this, if it doesn't go too high. If the combustion chamber volumes are porportional to the displacement, then: present CR = 9.5 x (738/652) = 10.75 I expect the 750 pistons lower this somewhat. Anybody have experience with this issue?

Regarding the possible out-of-balance - I presume the 750 pistons would weigh a little more than the 650s due to the larger diameter. Even though the crankshafts are the same part number, I imagine that the counterbalances are drilled a little to perfectly offset the weight of the piston, rod, etc. Perhaps the weight difference is inconsequential. Does anybody have experience with this?

One more question - Is it true that a KZ1000 engine will NOT fit in my 650 frame?

Thanks guys. Y'all are fantastic!

The 1000 motors will fit into a 650 frame with mods. But i was told you have to pull the motor to get the valve cover off. And i would think the frame would really be weak from such a big engine.