AHRMA Vintage Superbike Middleweight Racer

Can anyone speak to the downsides of using the Kz750 cylinder head with the kz650 stock pistons/bore? Do I lose squish band area or have any other negative impacts on the combustion area? Compression ratio?

I'm hoping to try to measure the volume of each tonight and compare cr's.

I do want to reiterate that I have no idea what I'm doing here and I'm hoping those that do feel free to jump in and slap me around a little. Please.

Found this while looking for a replacement throttle assembly. I wanted to remove the stock switch assembly (it was in really bad shape with the switches broken, faded, rusted, etc).

www.dimecitycycles.com/vintage-cafe-race...sembly-44-97780.html

I have this brake master cylinder that I was hoping to use - anyone know how I can calculate whether it will work with the Kz650C3's dual front calipers? What if I were to find some dual pot calipers - would it be big enough? Suppose we'd need to know which calipers they were first, right?

www.motorcycle-superstore.com/1/4/68/385...aspx?WT.ac=SLIsearch



Also looking for a replacement splitter to remove the switch/splitter that came stock on the bike. New lines as well.

Seems like something like this might be the cheapest route...not sure if it's a good route.

www.z1enterprises.com/Brake-Hose-10MM-X-...OLT-Chrome-3347.aspx

DoubleDub wrote: I have this brake master cylinder that I was hoping to use - anyone know how I can calculate whether it will work with the Kz650C3's dual front calipers? What if I were to find some dual pot calipers - would it be big enough? Suppose we'd need to know which calipers they were first, right?

www.motorcycle-superstore.com/1/4/68/385...aspx?WT.ac=SLIsearch

Also looking for a replacement splitter to remove the switch/splitter that came stock on the bike. New lines as well.

Seems like something like this might be the cheapest route...not sure if it's a good route.

www.z1enterprises.com/Brake-Hose-10MM-X-...OLT-Chrome-3347.aspx

i would just buy an ebay master from a modern bike. if u can go with a radial master in your class, that would be best . if not, just about any modern master will work. get 1 from a very popular bike, so u can get a replacement lever fast and cheap if u brake 1. i put a zx636 radial master on my cbr track bike. i have a spare master from my cbr if u want a freebee. it needs a bar clamp and lever though.
as for the splitter. the bolt u show is for adding dual lines to a master so u would not need a splitter. i should have a few spares . yours for free if u go that rout.

DoubleDub wrote: Found this while looking for a replacement throttle assembly. I wanted to remove the stock switch assembly (it was in really bad shape with the switches broken, faded, rusted, etc).

www.dimecitycycles.com/vintage-cafe-race...sembly-44-97780.html

do some more homework on this one.
make sure your cables will work before u jump in.
i used some ebay parts to make a 1/5th turn throttle. r1's use a shot twist throttle tube. the outer housing looks like the 1 in your pic. i use a cbr1000 exterior with a r1 inner .
a short turn helps , so u dont have to reposition your hand and just makes it feel better on the track. does for me anyways.

DoubleDub wrote: Can anyone speak to the downsides of using the Kz750 cylinder head with the kz650 stock pistons/bore? Do I lose squish band area or have any other negative impacts on the combustion area? Compression ratio?

I'm hoping to try to measure the volume of each tonight and compare cr's.

i think the 750 valves are bigger, so thats a plus. measure them. measure the O.D. of the chambers. if the 750 is bigger then u would loose squish, and compression. if the od is the same and the volume is more, u would only loose compression.

Larry mentioned that the head itself should flow a bit more air too...I'll make measurements and get back to all of you.

Thanks for the pointers Mark. Always good to get feedback, of any kind.

Glad to help.

I just finished measuring the diameter and volume of the combustion chambers - very surprised by the results.

Here is my super duper accurate measure method.

First up is the Kz650 head:
a.) Used a cheap Harbor Freight digital micrometer for extreme precision and proper technique (that's sarcasm folks) showing a 60mm~ish diameter combustion chamber:



b.) Filled the combustion chamber with water and used the ever precise turkey baster to move it into a very accurate liquid measuring cup (again, sarcasm):





And repeat on the Kz750 head:






From this extremely precise exercise I would have to say that the two combustion chambers are identical.

I know it looked like the 650 combustion chamber held more water, but I think it was the angle I took the picture at. Sorry about that. I also had the valves off on the 750 head and some grit got in between them and the seats that I had to clean up. Had a leak the first time I tried to measure the volume. I really need to give this head a bath...

I also just measure the lift on the cams. I thought the Kz750 cams were taller, but they're actually shorter on the intake and taller on the exhaust only. :huh:

The cams I am comparing are from (assuming they were never swapped):

1. 1979 Kz650-C3:
Intake=37.78mm x 28.07mm
Exhaust=35.76mm x 28.07mm
Lift= 9.71 mm / 7.69 mm
or .3884 in / .3076 in

2. 1982 Kz750-E3:
Intake=36.25mm x 28.15mm
Exhaust=36.20mm x 28.15mm
Lift= 8.10 mm / 8.05 mm
or .324 in / .322 in

I think...unless I screwed up measuring something. That .388in intake lift on the 650 seems high. But what do I know?

The 1982 Kz750-E3 model is a guess based on the Engine ID #.