need the down low on kz650 gpz mod

This is what i got, KZ 650b 1978, I plan on using the kz 650 head with gpz 750 cams and gpz 750 pistons and valves and springs. My questions come in by asking what do i need to do to get the valves to work, also woudld it be okay for me to use the used set of pistons rings i have coming in with the pistons (low milage motor). Also how do i degree my cams to get the most out of them.
Is there any other problem i am going to run into.

PS i look up the mods on google but i didn't see any about using a 650 head. Thanks

Hey odl666 - Here is what I have done with my 650 head, Gpz750 cams and intake valves.

I had the valves trimmed 0.015" by the machine shop that also milled my cylinder head 0.010" to clean it up.

Given that the GPz valve has a larger face than the 650's I had new larger valve seats put into the head. Get them to do the angles on the seats at the same time. The machine shop will need the cams, springs etc. to measure everything exactly. It is unlikely that the shims you had in the 650 head with the 650 cams will fit. If

I recall, on average I had to go with shims that were .15-.20 thicker when I switched from the Kz750 cams to the Gpz750 cams. As an example, if I had a 2.45 shim with the Kz750 cams I had to put in a thicker 2.60 or 2.65 shim. When you compare the base lobe circumference between the 650 and Gpz cams you will see a noticeably thicker lobe on the 650.

As far as using the old rings on the Gpz's pistons you might be able to get away with them but it would be a good idea to have a machine shop check them for you. If you put in new rings you will need to hone the cylinders. I would recommend a new set of rings and a hone just to make sure everything is good.

Cheers-Colin Firth-Ontario Canada

Thanks I was gonna get the cylinders bored and honed and thought that i should use new rings, just didnt want to spend the money (poor college student). But i hope to sell some of my old parts and save some cash to get the machine work done. The only thing is i am from new mexico and kinda of scared that they wont know what there doing. Anyway thanks for the help again, haveing you explain the valve thing helped out now i know what i need to tell them and maybe they'll be able to take it from there.
I am thinking of taking more off my head, about o.025. Do you think that would be okay? Thanks for all the help nice to know that theres someone to ask questions to. Thanks again and have a good one!

This site is worth a good read. It may answer some of your questions.

gpzrider.lagemann.org/technical/FAQ2000.htm

Cheers-Colin Firth - Ontario Canada

This site is a good read. It may answer some of your questions.

gpzrider.lagemann.org/technical/FAQ2000.htm

BTW if you are using the 650 cylinders the biggest current piston/bore you can go with is the Wiseco 700 cc kit.

It is possible to have the old 650 cylinder sleeves removed by a machine shop and new 750 cylinders pressed in but why not just get the cylinders from the donor bike that is providing the pistons, rings and cams.

Better yet, why don't you just stuff the whole GPz750 motor into your 650 frame? There might be a little playing around with the wiring but you will have a bike that really hauls the mail with factory reliability.

Just my 2.5 cents worth:)


Cheers-Colin Firth - Ontario Canada

79 KZ650SR with 83 GPz750 motor.

steell wrote:

79 KZ650SR with 83 GPz750 motor.

Steve when you did this bike did you convert this motor to use the clutch pushrod setup or change over to a GPZ style clutch cable. I'm about to stuff a GPZ 750 motor into an 81 750 LTD and I'm unsure if the GPZ motor has the hole machined in the cases for the pushrod.

We used the GPz clutch cable, the stock GPz750 sprocket is a 15 tooth 630 and leaves no room for the pushrod. That bike has a 18 tooth 530 sprocket on it, I was lucky enough to find a couple of offset 530 sprockets left over from a group buy.
Had to use the GPz throttle cable also, the 650 cable won't fit the GPz750 carbs.

GPzInfested is impressed with how it runs

BTW if you are using the 650 cylinders the biggest current piston/bore you can go with is the Wiseco 700 cc kit.

It is possible to have the old 650 cylinder sleeves removed by a machine shop and new 750 cylinders pressed in but why not just get the cylinders from the donor bike that is providing the pistons, rings and cams.

Well i heard that kz 650 sleeves were the same size as the 750 sleeves, the only thing different is the 750 sleeves have a bigger bore making the 650 sleeves with thicker walls. Dont know though but a fellow kz650 owner told me this. Makes sense though right?

odl666 wrote:

BTW if you are using the 650 cylinders the biggest current piston/bore you can go with is the Wiseco 700 cc kit.

It is possible to have the old 650 cylinder sleeves removed by a machine shop and new 750 cylinders pressed in but why not just get the cylinders from the donor bike that is providing the pistons, rings and cams.

Well i heard that kz 650 sleeves were the same size as the 750 sleeves, the only thing different is the 750 sleeves have a bigger bore making the 650 sleeves with thicker walls. Dont know though but a fellow kz650 owner told me this. Makes sense though right?

You cannot bore the 650 sleeves out to 810. There isn't enough meat in the cylinder walls. To get to the 810 displacement you have to start with 750 sleeves.

When I had the 750 cylinders bored for my 810 I was surprised how little material was left and this was most noticeable on the bottom where the chamfer was. From the factory, the 750 cylinders had a nice thick angle on the chamfer which made installing the pistons and rings quite simple. With the bored cylinders the chamfer is almost non-existent and makes putting the pistons and rings in a real tight squeeze.

There were a couple of other displacement big-bore options for the 650. MTC had a 784 kit but I don't know anything about this kit aside that its pistons had a 12.5 to 1 compression ratio. This would not be very practical for the street and would likely require racing gas. Add a milled head to this and the compression would be even higher.

One of our members here on Kzr (Mark Wing) has a 716 Yoshimura kit in his '77 Kz650. You might want to contact him for info on this package which may or may not be available still.

Lastly, I seem to recall there was an 880 kit (I believe this was the cc.'s) but again these aren't very common and the walls would be so thin that you might have some serious overheating issues to deal with.

Cheers-Colin Firth-Ontario Canada

"You cannot bore the 650 sleeves out to 810. There isn't enough meat in the cylinder walls. To get to the 810 displacement you have to start with 750 sleeves."


Yeah i understand about not being able to bore the 650 sleeves to 810, but i was just gonna go to the 750 stock gpz pistons. I think the the 750 are only actually a 736 making it a big difference between 810 and a 650. I was gonna take them to a machine shop to see if there would be a problem with the walls being to thin for the 750 pistons.
The only reason i say this is because a fellow kzer told me that the 650 could be bored to a 750 with no problem but you know words are. I guess i'll just find out when i take them in. Thanks for all the help! have a good one i am sure i will have plenty more questions for you soon. Thanks again reborn

For the 1980 Kz750/4 I seem to recall that Kawasaki used the exact same cylinder block casting as the Kz650.

Kawasaki simply re-sleeved with larger steel cylinder inserts which brough displacement up to 738 cc. This model was designated as a 750 to round things off.

Cheers-Colin Firth-Ontario Canada