Cracked block near chain tensioner - KZ750 L3

Patton wrote:

Is the long white line an extension of the crack?

Looks a lot worse in your blown up photo :ohmy:

750's have a head bolt down inside the cam chain tunnel in that area. Someone may have been taking the head off and missed it.

OK. I'm in the market for a new block. I'm in Seattle. Who's anywhere near me? Anyone have a black one? It'd look weird to have black/silver/black, but I'd definitely take it.

So I can take the sleeves out with an oven but not put them back in? Why wouldn't they slide in as easily as they came out?

(Side question, since I'm gonna visit a stranger soon and buy parts off his 1981 KZ750.. will that bike have the same igniter and ignition coils?)

staniel wrote:

...gonna visit a stranger soon and buy parts off his 1981 KZ750.. will that bike have the same igniter and ignition coils?)

Per kawasaki.com -- the igniters have different part numbers.
But ignition coils (each side having different number) seem the same.

If needed, here's some help about using kawasaki.com
Click > kzrider.com/index.php?option=com_kunena&...w&catid=13&id=376734

Good Fortune!

Patton, that is magnificently useful. I've only been able to cross reference from kz.mbsween.com. Thank you!

I see now, the igniters are different. Still, if the price is right, I'll buy it and hope. I found one online for $85 as well.


So, the current plan is to get a new block and swap sleeves. Regarding tribology, how important is it to maintain the angle? If the 60° mark on a piston ring seats itself to the 60° mark on the sleeve, what happens if the ring rotates 15° during the reinstallation? Do you have to break it in again?

Could the crack have been caused by a loose head mounting bolt? I did not retighten them after heating and cooling the engine...

staniel wrote:

...have to replace the block, which is hilarious. At what point do you simply replace the whole engine with one that works?

Would meanwhile consider Larry's suggestion to Tap the top bolt hole to 1/4", or next slightly larger size of whatever thread that would enable a snug torque (or perhaps heli-coil or threadsert). And ride. Keeping a close eye on the situation.

Am perhaps overlooking some catastrophic potential, and must defer to Larry and others for more competent advice about risk of causing additional engine damage or bodily injury.

Hoping for more input as to feasibility of the less expensive alternative.

Good Fortune!

I am under the impression that piston rings rotate in the bore, if that is true it would not be important to match the angles.

When my 650 needed the head replaced (I buggered the origional head removing it) I just used the top end from a donner motor that was disassembled but had 10K on it (20K miles less than my motor). I swapped the blocks and pistons without knowing which piston came from wich hole. The motor has 125-135 psi in all holes my mechanic said it held air well in the leakdown test. Either I got very lucky, or it just isn't as critical as people make it out to be.

try what larry said first and clean it well and jb weld it for leaks.

Larry said to "relieve" the crack before JB welding. Does that just mean to grind it out a little for something for the JB to stick to?

Yes, what is it to stress-relieve it in this case? Isn't there inherently going to be stress on this joint?

New bolts were possibly too long, bottomed out and pushed that piece out.

Stress relief is to grind the aluminum below the depth of the crack. The blown up photo shows the crack to be worse than I initially thought it was.

This may or may not take care of the situation. No guarantee but it's an option that doesn't require a tear down.

staniel wrote:

...I used two new bolts in tightening the head on and these bolts come straight through to that point. I bought stainless steel ones and ground them down to size....

As TerryK suggested, New bolts were possibly too long, bottomed out and pushed that piece out.

Wouldn't hurt to remove the bolts and double-check for this possibility.

Good Fortune!