Z2 750 crank (Bossie the Kaw)

Ok, I'll do my valves this evening. Here it is. My last reading is 54.50. I took multiple pics because the measurements changed slightly.
TDC

BDC


54.51mm


Old gasket




Another pic of depth.


I'm now sure it IS a 750 crank. 54.51 - 1.40= 53.11.
Next is the compression test.
Steve

Yup looks like you got it.
Now what?
Pull the engine crack it and replace the crank and rods?

Maybe I'll list it on eBay for $9000 OBO like that fool, buy a 903 crank for $200 and maybe buy a bigger kit. :lol:
Steve

There is a flaw in the oil test CR check, that could be worked around if doing valve clearances - I'll leave you to work it.

over and out .

I'm satisfied it is a 750 crank. I also know I'm losing compression because of it. Too bad I didn't do this before I put in the new pistons. I could have done a CR test then and now. Oh well, I should be able to buy a 903 crank soon and list this one on eBay. I can't find any there so it should fetch some money.
Steve

I wonder if the KZ1000LTD crank and rods (still in the open case I found for $25 earlier this summer) is worth a tinker's damn.
Probably rusted tight.

www.kzrider.com/media/kunena/attachments/4138/IMG_0958.jpg

I know this is all a moot point but for what it's worth...
I just measured my 1015cc piston and the top of the crown, furthest point going into the combustion chamber, is 30mm from the center of the pin.
The top land, which is the flat of the piston before the crown starts, and where I said it was just about flush with my over bored sleeve at TDC.... is 24mm from the center of the KL250 piston pin.
That old picture you had from some Z2 Guru....of a used Z2 750 piston, mentioned the crown top was 36mm from the center of the pin.... and the top land of the Z2 piston looks at least 2mm-4mm thicker then my 1015 piston, again, which measures about 30mm from the center of the pin to the top of the crown.
That is at least a 4mm-6mm difference by eyeballing it.

So, the distance from the center of the pin and the very top flat area of the first compression ring (not just the crown) is larger in the Z2 750 piston.
That means to me, regardless of what the stroke is, the KL250 1015 piston pin is higher in the casting, with respect the pin center and the top land flat, thus lowering the top of the piston and the flat of the top land into the cylinder at TDC ...at least 3mm-4mm then the same crank would do with the Z2 750 piston if it was the right bore for the 1015 cyl block you have.
I guess it is redundant but there is where you lost that 3mm to 4mm of piston top and deck height issue and now a lower CR and probably combustion chamber PSI too.
I wonder how much real horse power is lost to this though?

Thank you for taking the time to check it out.
I was mulling all this over myself. Being the stroke is 8mm shorter, it stands to reason the compression would suffer. The stock KZ 1000 cranks are heavier than the 903 so they would be of no use to me. As it stands now, the bike is running great and I should be able to buy a 903 crank soon. Although it is a lot of work splitting the cases, I believe it will be worth it. Z2 cranks just aren't available making them worth a lot of money. It would be wise of me to change it out before any damage can occur.
I'm glad I did it when I did. You saw the center roller and the missing guide. A broken cam chain was imminent and total destruction of the engine could have been the result. Dodged a bullet on that one. :whistle:
I went back to the old style manual tensioner. I may install a heavier spring too. In 40 years I never had one fail.
Steve

As it stands now, the bike is running great

I guess that's the 'deal' with litre plus muscle bikes, always a load more than you need.

Good street cred chatting about race cams and high compression pistons, in the real world it is how it pulls on the road and about town with pump gas and a reliable lasting motor at FSM service schedules.

Re pm, That rare 750 crank, I think it may be scrap metal in USA but big money in other markets. If you list it online
make sure you have worldwide visibility. I've sold cars and bike parts all over the world, NOS 750 crank is $$$$$ if you can find one, also the super rare stuff you need to stick to your price and expect several months to sell to the right punter who really needs it.

Thanks, the trouble is, these things are almost bullet proof. If one goes bad, I shudder to think what the rest of the motor looks like. :ohmy:
Steve

Just read thru this and was thinking since its all miss matched you could just put kz1000J pistons in it to make up some space.

the trouble is, these things are almost bullet proof.

...that is the problem, anyone want a good in service spec 550 /750 crank and rods - yous for a bottle of red. Kawasaki were too clever in their engineering , these ££££ forged/pressed cranks now you almost can't give away.

Customer complaint: Dear kawasaki, please make our cranks more crappy to give the small guys a chance of maiking some dough here 30 years later to fund our restoration projects :laugh: .