I’ve got a 1980 KZ750 engine and it’s kinda my pet project. It was given to me for free, in pieces, in a box. I’m a machinist by trade, so it’s been sitting in my shed for some time, but the wheels in my head have started to turn in kooky directions... the cylinder and head are off of the bottom end, doesn’t appear anything is actually broken, but the sleeves do have a bit of rust, one quite a bit more than the rest. I know there’s a few options out there for overbore (69mm Chinese 810 with cast pistons, or Wiseco high comp forged 810cc) but... me being me... I want to see just how insane this thing could be... theoretically, if the engine was factory assembled how I think it probably was, with the cylinder liner sleeves pressed into the block, one could bore them to an extremely thin thickness, then have them nikasil plated... of course finding one off pistons would require $$$$ but I kinda know a guy, I could go full Burt Munro style, but with a little modern tech, CAD my own factory pistons up, but then add to the diameter, and 3d print a set of 4 of them, then lost wax cast each one, to end up with my own custom size piston, and do the necessary finish machining work myself in my lathe and mill. I’m thinking 74mm bore would be possible, with the factory 54mm stroke, and with the bored nikasil plated and also getting the pistons coated (ceramic coating the domes, Teflon coating the skirts) it could make one heck of a mean little rev happy 930cc monster, and the displacement would be enough for gobs if bottom end torque, I could drastically port the head (I know all about the horrid casting lip inside the factory head, just wish I could increase the valve size, but the deck just won’t allow it) I wouldn’t go too ridiculous with the compression, keep it in a cast-piston and pump gas friendly 10 or 10.5:1 ratio. Is there anything else I could do to further add more cubes? Shy of a full billet cylinder block or starting with a whole other engine? I wouldn’t need it to last 100,000 miles, as it would just be a pet project, just curious what it could really do with a bit of mad scientist engineering.
I think machining some new larger liners would be a more viable option than messing with plated bores. And most of the big piston houses will design you a piston so no reason to go off the rails there either. Sounds like a viable project, but you won't get near the bang for the buck quotient of the cruzinimage pistons.
Is there a bigger stroke crank I can get without custom regrinding the journals off center? Granted, if I do that I’ll need to move the wrist pin higher on the piston or custom design a shorter rod, (maybe even make my own Ti rods if I want to go completely psycho) depending on how much I can wiggle the wrist pin on the piston. Rod/stroke ratio starts coming into play, but if I just go 1.5mm off center on the journal regrind, 1.5mm higher wrist pin to piston dome height, that’ll give me 3mm more total stroke, which would be a huge jump to 980cc!!! I had considered just going to bigger liners, but the nikasil also has another benefit of lowering the drag, less friction. Bigger liner will hold more heat, thin liner will dissipate heat better (more modern engines just use bare aluminum block with nikasil to get best cooling as well as the other benefits of nikasil) Lots of variables to toy around with... haha
My thoughts are, with the equipment I have on hand, I could go 74mm bore pretty dang easy. Even casting my own custom pistons. Could even do it for about the same price as the cruizinimage 810 kit, given that my after hours evening time is ‘free’ and I can get a set of genuine Japanese rings for around $60 if I go with an actual factory bore size (Yamaha FJ1100 uses 74mm bore to just name one)
I know of a GPz750 turbo that has KZ900 cyl. liners and a 3 mm stroked crank. 1010 cc and make over 300 hp.
And yes you can see the liners between some of the fins
1980 KZ650 F1
Wiseco 810cc kit.
Zukiworks racing ported head.
VM 29 smooth bore's.
Dyna 2000 Ign. w/Dyna mini coil's
APE cylinder stud's and nut's.
APE valve spring's.
APE Track King clutch.
V/H KZ1000 sidewinder.
3.5x18 laced to a KZ1000 disk hub.
150/60/18 Shinko 006 Podium.
Well I just purchased a set of sleeves lol guess I’m committed now.
The 900 uses the same 66mm bore as the 750, so they’d be gaining zero cc there. I don’t have a GPZ11 engine laying here collecting dust. (I don’t even have a KZ/GPZ frame, gonna slap it in my raked out, stretched frame and swingarm CB frame haha)
Only problem I could see with that would be that iron doesn’t dissipate heat as well as aluminum does... but they make plenty of engines with just iron cylinders, fins and all are iron, look at any old HD or BSA or Triumph, all used solid cast iron cylinders before about 1970. HD took until almost the 90s to start using sleeved aluminum.
Hey Daveyg search for Worlds biggest KZ650...... It was one of my 1st posts way back in 06. Search google and here for big bore kits for the KZ650 too and you'll pick up more info. If I had it to do over again I'd stick with the 810 Weisco kit (proven to be a strong running and tough set up ) or maybe the 831 MTC pistons if you can still find em. Have a 1980 750 block and still might someday but am running outta years fast.
1978 KZ650 b-2
700cc Wiseco kit 10 to 1.
1980 KZ750 cam, ape springs, stock clutch/ Barnett springs.
Vance and Hines Header w/ comp baffle and Ape pods, Dyna S and green coils, copper wires.
29MM smooth bores W/ 17.5 pilots, 0-6s and 117.5 main
16/42 gearing X ring chain and alum rear JT sprocket....
The following user(s) said Thank You: Nessism, daveyg
Thanks for that info! I already found your old thread. I’m not really looking for manners or longevity really haha. Just wanna say I did it. I’m probably gonna run a pair of 40mm mikuni round slide carbs, one feeding cyl 1&2 and the second feeding 3&4, exiting out of a set of headers and a straight pipe off of each header.
Now for some math. From the fin to the casting I get approx 28mm, from the fin to the ‘bore edge’ of the existing bore (with liner removed) is approx 35.5mm, meaning I have roughly 7.5mm wall thickness before the liners would be directly exposed to the air in between the fins. Which is a radial dimension meaning there’s roughly 15mm diametrically. Should have plenty of room for the bigger sleeves I think.