kz650 big bore to 830cc

Hey folks, I'm looking into getting a '79 KZ650 to learn custom/wrenching/etc. I saw a few of these online with a big bore kit out to 830cc, but I can't figure out how they achieved it, would it be possible to get some pointers or advice? Thanks.

You cannot bore a 650 out to 830. Maybe someone bored out 750 cylinders and put them on a 650 bottom end? I believe 830cc kits were available in the past from Wiseco, but I thought the maximum safe bored out size for a 750 was 810cc. Ed

Beware of CHINESE piston kits.
Steve

Cruzin Image piston kits seem fine with many on the road. 810cc and requires a 750 cylinder block.

Nessism wrote: 810cc and requires a 750 cylinder block.

Do you have to machine the 650 case top half to fit the 750 cylinder block? Or does it bolt right on?

The 1980 KZ750 is the only cylinder block that will work with the roller cam chain.
Yes you do have to bore the case to fit the larger cylinder liner's best I know.

Colin Firth AKA reborn650 in Sudbury Ontario did a 650 to 750 to 810 back in late 2006 early 2007 Search here for the many threads he posted within that time frame. No single project thread

Here's one where he describes using 750 sleeves (which he later rebored to 810) in a 650 block.
www.kzrider.com/forum/2-engine/132331-75...ers-650-cases#132396

Beautiful bike which I got to see one Summer evening in Colin's workshop together with a small group of of local KZ enthusiasts and KZR members

Yes, there are many threads on this topic. A search will turn up lots of info. Slam this search phrase into google and start reading... site:www.kzrider.com 810

As I understand it you don't need to bore the cases per say, just dremel out a little aluminum in select spots in order to allow the 750 cylinders to fit. Regarding what 750 cylinder to use, you need the type that allows the use of the roller guide system. The 1980 cylinder is the one people commonly talk about but I have a 1981 engine and the cylinder was the same so it's not a 1980 specific part.

I have built quite a few big bore 650 based motors.

A 70 mm piston puts it out to 831cc so if you Google 830 you wont get too much info.

810cc is a 69 mm piston.

MTC offered a 831cc kit in 8:1,10:1,13:1 compression ratios but stopped making them somewhere around 1990.

I currently have that kit in two motors. There are not too many people running this kit out there, I only know of one other example and its a turbo kit.

Here is one of mine :



Here is the second bike :



The stock 650 liner can only be taken out to 65 mm = 720cc but ends up being extremely thin just like a 750 taken out to 810cc so you need to run a oil cooler to make it live.

I found a way to put a custom liner into a 650 block to accept the 831cc pistons that the liner ended up thicker than the 810cc version in a 750 block... It is not cheap at all so I always suggest sticking with the 810 kit.

The 70 mm pistons for the Z1 do not work so you have to go the custom piston route.

The last time I checked the custom 70 mm pistons were over $1100. By the time you get all the machining done to the liners and the barrel, just that part of the motor costs about $2000. It really wont run optimal unless you have a ported big valve head, big cams, and big carbs on it - The motor just ballooned up to $4500 and its still not as fast as a worked on 1075 Z1 !

The 810cc version running a GPZ head is the way to go, put a set of CR29 or RS34 carbs on that and it will fly.

Injected wrote: The stock 650 liner can only be taken out to 65 mm = 720cc but ends up being extremely thin just like a 750 taken out to 810cc so you need to run a oil cooler to make it live..

Are sure you need oil cooler?
That means you need oil cooler on bigbore 810 upgraded from gpz750 engine also, I have not been notify todo that?

What is left on that liner is super thin and as Wiseco found out with the 720 kit, it could overheat making the liner distort thus loosing ring seal or worse. They discontinued that bore size and now only offer a 700 cc version. I think they had a lot of locked up (seized) motors with people coming back with warranty claims.

If I was running a thin liner like that it would not hurt to run a cooler, it depends on where you are and what the ambient temp is locally. Your in Norway so summers are cool so you will probably be OK, same as with guys in the UK. Around here the summers can reach 32-34C so that motor would cook the oil in no time. A thick liner dissipates heat better - Ever seen the liners on a stock Z1?
If you want your motor to live longer then it is a good idea to hook one up.

Injected wrote: What is left on that liner is super thin and as Wiseco found out with the 720 kit, it could overheated making the liner distort thus loosing ring seal or worse. They discontinued that bore size and now only offer a 700 cc version. I think they had a lot of locked up (seized) motors with people coming back with warranty claims.

If I was running a thin liner like that it would not hurt to run a cooler, it depends on where you are and what the ambient temp is locally. Your in Norway so summers are cool so you will probably be OK, same as with guys in the UK. Around here the summers can reach 32-34C so that motor would cook the oil in no time. A thick liner dissipates heat better - Ever seen the liners on a stock Z1?
If you want your motor to live longer then it is a good idea to hook one up.

I understand, thank you for the information.
So Maybe I shall install oil cooler with termostat in the future. As you say temp here is properly max 25 in the summer.