Z2 750 crank (Bossie the Kaw)

swest wrote: No the sleeves dropped in. I didn't change anything. I had no idea the rods were shorter and I'm not sure they are that much shorter. Time will tell.
This IS a unusual build.
Steve

Yeah, so how did it work out. From the outside something doesn't add up. But it apparently works, will be watching.

Also these forum is full of type A personalities... and shit hits the fan every now and then. Dont take it personally.

Thanks Ed. I had no idea the Z2 crank had a shorter stroke in 87. I knew it was lighter and I had a friend with a CB 750 bored out to 1015 and that bike was quick. I've talked about it here. When I found the Z2 engine, it was complete. The head had broken fins but the valves were like new so I used them, at least I think I did. That was a long time ago. In 78, I had it bored out to 1015 but the bores were slightly out of line. After the wreck I had Clupper racing bore the 750 sleeves to 1015 and used my cast pistons. That's when I had the crank welded by V/H and ran it that way until 98. It sat for 15 years until 13 when I started to get on the road again. The compression land on one piston was deformed so I had to buy new Billet pistons. I screwed up and ruined one of my new pistons. I thought I had only scored the bores, so I won a 1015 set up on eBay. turns out I ruined another piston. I'm now running stock 1015 pistons in the 1015 block. I'm semi retired so money isn't flowing like it did before. It's all out of pocket. I'll be dammed if I'll tear this thing down just to show some horses pittute what I have. With a 903 crank, this bike would walk away from him. There's no reason to "brag" about having a 750 crank if it wasn't true. It is just so.
Steve

If I had known about this site, I would have photo documented my build in 13. I did take some pics but I was excited about getting Bossie back on the road and didn't take more. This time I have the opportunity and will. My apologies to the members that have to see this discourse. I've done my best to refrain from calling his bike a POS like he did mine only as to not insult other riders of the same size. This is not about me or him. It's about the bikes and what we do with them.
Steve

Here's a link that show the specs, including bore and stroke, for the Z2. It shows the Z2 stroke as 58mm. On that same site the stroke of the Z1, KZ1000, etc. is shown as 66mm. Ed

www.motorcyclespecs.co.za/model/kawasaki...ki_z2_750rs%2073.htm

Steve, I am not taking sides either way. And have no reason to doubt your claim. Only thing is I don't believe you can end up with a 1015 motor. Here is why. Cylindrical volume is V=πr2h (the radius r is squared). So in your case it would be bore for a 1015 motor is 69.4 mm (diameter) which is 3.47 cm radius. And the crank on a Z2 is 58 mm which makes the cylinder volume highiet of 5.8 cm. plug everything you get the following displacement

(pi)*(3.47)sq*(5. then times 4 (four cylinders) = 877.60 cc

Smaller than your original 903 cc motor. Now, can the rods from your 903 engine have been used in place of the 750 rods (don't know if that is possible, I have no clue)? In that case, it would have made it a 1015 motor. But like say, I have no doubt you that you are using that crank. Don't have to prove anything to anyone man. So don't get rushed into anything.

It does seem to be a little detuned with the stock 1015 pistons. With the cast or billet pistons, the deck height was even. With the stock ones, it was about 2 mm lower thus lowering compression. All i had then was a German made caliper so I didn't measure it. I now have a digital one and will show the depth with the stock pistons and compare with the 10.25/1 Wiseco's. 58-66 is quite a jump and 8 mm would be hard to miss. If the throws on the crank are shorter, wouldn't the rods be also? I was oblivious to this issue until now. I want to know too. I remember a stamp on the counter balance and the rods have markings as well. It would be helpful to know what the Z2 markings are to compare. If I have to go back to a 903 crank to get the ponies this bike deserves, then so be it. There was interest in this crank for a member's turbo build. We'll see.
Steve

Just checked eBay for a Z2 crank. Lots of plain bearing KZ 750's and some triple cranks too. No Z2 750 cranks. I don't trust eBay and If I do buy a 903 crank, it will probably be from The Old Kaw Guy. He's always treated me right.
I bought a new throttle cable while there. The one I have is almost two years old.
Steve

Bought these in 13 too.
Steve




$250 OUCH

It seems to me that part of the confusion is that overbore piston kits are typically labeled with the resulting displacement, not the piston diameter. Wiseco sells a 1015, 1045, 1075, etc. So it seems perfectly natural to say that you have a "1015 kit" in your engine even if you were using a short stroke crank. We all understand that you wouldn't actually have 1015cc, but it's a very easy way to communicate which pistons you purchased.

I think the idea of running a short stroke crank seems pretty cool, depending on how far into the red you can safely build the valvetrain to go. Modern bike engines are all way oversquare.

The stroke of the Z2 crank has been established, but no one seems to know if the rod length was altered. It seems possible that Kawasaki used the same deck height for both the Z1 and Z2, and just used longer connecting rods to compensate for the shorter stroke length. If that were the case, then a Z2 crank should drop into a Z1 with no changes at all. Does anyone know the rod length, or relative deck height of a Z2 compared to a Z1?

I think the idea of running a short stroke crank seems pretty cool, depending on how far into the red you can safely build the valvetrain to go. Modern bike engines are all way oversquare.

Yup, also I think just boring out with oversize pistons alone won't make big power gains without more cam and other tuning work. It is more about a motor's valve time area than capacity imo.

Has a 'bored and stroked' under square motor been done before on a zed?

etbike3135 wrote: hows that 4 valve piston working in your motor?

Im wondering what kind of camshafts you use with 1 4 valve piston.

Tyrell Corp wrote: I think the idea of running a short stroke crank seems pretty cool, depending on how far into the red you can safely build the valvetrain to go. Modern bike engines are all way oversquare.

Yup, also I think just boring out with oversize pistons alone won't make big power gains without more cam and other tuning work. It is more about a motor's breathing than capacity.

Has a 'bored and stroked' under square motor been done before on a zed?

If you could find pistons with the right pin location it would probably be a riot to ride in a light bike.