Some 903cc questions

Hey all, just looking for some info.

Does anyone know the Outside and Inside diameter of z1 (903cc i believe) cylinder sleeves?


What is the largest popular bore that folks use on those sleeves.

What I am thinking here is how thin can the sleeves get and still be streetable with a good service life.

Thanks! Any information is appreciated!

I don't like under 2 mm wall.

with stock 903 sleeves about the biggest you can go is 1015 but if you want to go bigger you can keep the block and bore it for bigger sleeves that you go out to 1197 with and still keep a stock appearing engine.

Well what I am wondering is what, if any use the 903cc and other liter bike parts could have in a kz650/750 platform.

I noticed the wiseco 810 kit is a bore of 69mm and the 1015 kit (which would put a kz650 up to 857cc) is only 2mm larger.

That got me thinking about how much room there is on a set of 650/750 jugs and if larger sleeves could be fitted relativity cheaply (903 sleeves for example).


I guess the next question is how similar are the dimensions of the pistons 810 vs 1015?

Also how thin is too thin when dealing with the block? Is there any rule of thumb for how much meat you need to leave in the block itself to keep the liners in place?

Interesting, I am doing the 810 conversion shortly, and I didn't think of THAT ONE !! Press 903 sleeves into a 750 block , yeah, Thad be one killer smallblock. Wonder if the rest of the engine could take it?? sounds cool though!!

MAC:laugh:

I would think the thickness limitation would be not breaking or splitting the jug when pressing the sleeves in. Since the head studs go all the way into the crankcase it's not going to blow the cylinder apart vertically.

Also the distance between the centerline of each cylinder bore and the edge of the stud hole is going to be a limit.

well whatever the limits of the cylinders, I now know my rods will handle it.

cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll...em&item=220483161175

Just picked those up, now back to the question at hand.


Does anyone have a 1015 kit that is not in a motor? I can send you a stock 650 piston and you can take some measurements for the forum.... let us know what it would need in the way of wrist pin, and how it compared in height from pin to dome. I think those are the only measurements that matter other than wall thickness on a 750 block.


If 750 sleeves can go +5mm (to take a 1015 kit) or if 903 sleeves can be convinced to fit, I would love to make a 860cc kz650.

hey rocco,
i do have a 1015 kit with sleeves in a 900 block.
you know the number and what i want.

but for christ's sake, just buy a liter bike all ready would you?

you know the local connections that would make it scream and performance parts for a 900-1000 are easier to get then for a middle weight.

if your a good boy, maybe i will show you "the vault" :woohoo:

Steve, I hate when people tell me to buy a new bike. I get it from my friends all the time.

Why hot rod a kz650? Cause I want to... If I was just looking for power I would go out and buy a zx14 and be the fastest thing on the road. Honestly there is no reason to start with ANY 30 year old machine when you want to build a performance machine. Unless that is the machine YOU want to build.




Now Steve could you measure up the parts and let me know what it would take to run the 1015 pistons in a 750?

I think all that i need to know is...

Outside diameter of the 900 sleeves
wrist pin size
distance from wrist pin to piston dome
and casting thickness on the 750 block


The whole idea comes from an article I read about kz650's built to race in the 1970's and apparently the first guys looking for the most powers used z1 900 pistons to get more displacement.

I believe the stock 900 pistons (66mm I think) would only give you 730cc's or somewhere in that neck of the woods.

i don't have any pistons in front of me right now but the wrist pin size is 17 mm for the 73 to 82 900 and 1000's also the early gpz 1100 the 83-84 gpz 1100's are 18mm.

that big bore with the short stroke and a good head would be insane if you could make it work! but would it work though?

hardr0ck68 wrote:

Steve, I hate when people tell me to buy a new bike. I get it from my friends all the time.

Why hot rod a kz650? Cause I want to... If I was just looking for power I would go out and buy a zx14 and be the fastest thing on the road. Honestly there is no reason to start with ANY 30 year old machine when you want to build a performance machine. Unless that is the machine YOU want to build.

i was not trying to insult you or your bike at all.
all i was saying was the bigger bikes have more readily available parts and the motors are easier to make power out of. your kind of limited for real good performance parts. lucky for us a.p.e started a service for our cams again.
i still have the 784 kit, andrews cams, ported head and smoothbores for my 650.
i spent more on those parts then the 1260 motor.
both are 32 year old bikes and i would not trade either for a new zx-14............