TOPIC:

One of the most annoying parts of my first top end job was a breaking head bolt. In fact, I can't be sure it wasn't the ancestor cause of the very worst part of my last top end job, a crack in my block which necessitated my second topend job .

Well, last night I was putting it all back together. I got the head nuts tightened to 4mkg per the Clymer manual specs. I started torquing the head bolts. I knew their tendencies, so I elected 3mkg instead of 22ft-lb (3mkg is less torque than 22ft-lb, both are the spec). They started to feel soft, but were still moving. Finally, it happened again. A head bolt snapped.

I've attached two images.

The first is where and how the head bolt broke. It was the same both times. At least it breaks above the threads!



The second image includes one of my last two remaining head bolts, one of the broken ones, and the bolt I used to replace my head bolt on the first rebuild.



Are exploding head bolts common? Is the taper there so that they explode conveniently? I've read that they are made intentionally to stretch out - is that true? Are they one-time use parts? Does the heat ruin them?

Am I a fool for using a stainless bolt to replace them? Is the stainless replacement bolt I used the cause of my cracked block?

I'm definitely accepting speculation on this. I would rather not have to order OEM head bolts, considering I've never tightened one down and not had it break and it means I have to wait a week to build this thing up.

I can't tell scale from photos, but those look like the smaller 10mm bolts on mine they have to help prevent oil leaks. The spec on those is NOT 22 ft-lbs for sure, its about 100 inch-pounds (maybe eight foot pounds). On mine, the large head nuts that screw down onto the studs spec at about 30 foot-pounds, but the smaller bolts are way less.

These are 8mm threads with a 12mm bolt head. Is that what you meant?

An 8ft-lb torque spec would certainly explain the breaking. It would also explain how I cracked my block: torquing it to 22 with SS bolts!

I still won't wait for the OEM bolts, but I still have a couple of these head bolts (one from each of the engines I have taken apart) and I'll throw 'em in there. With Locktite in case 8ft-lbs is too little.

Here's a KZ750-L3 Page. MBSween's KZ750L3 Page
search tags tagz mbsween KZ750L3

I have several MBSween pages bookmarked and I have the GPz/KZ manual on my computer already

However, I never read it for torque specs.





There, at the bottom of the first page, it says torque the nuts to 18ft-lbs to start, then up to 29. The head bolts it still says to tighten to 22. Maybe I should invest in a fancy torque wrench, in case my mechanical one is bad somehow.

I've decided to just try installing them again, torquing to 22, and if they break, I'll order new ones. Maybe they're old and cruddy. I just don't look forward to the feeling when I'm turning them and the torque doesn't go up anymore.

They are probably torque to yield bolts, which are single use. I would just order new bolts and not worry about the new ones breaking. Might also be good to borrow a known accurate torque wrench to install them and then check yours against it.

Maybe someone with a Kawasaki Factory service manual can double check the torque specs. It would not be the first time Clymer just took a wild guess at what they should be. Ed

The bible on MBSween confirms it, as well as a Kawasaki dealership tech guy (who looked it up). 22 is the number, but I'm still afraid that applies to a different kind of bolt or that these bolts are one-time-use only. That would be a silly thing.

I'm afraid to go with the home-made stainless steel ones. Can't afford to crack another block.

I would never replace any of the bolts with stainless. Most stainless steel is much softer than carbon steel ones. That's probably why they broke off. You can see the stretch that caused it. Bob

Amen on stainless being weaker and softer than carbon steel. You should see what an accidental double charge of powder in a 45 ACP does to a stainless barrel and compare to a carbon steel barrel. The stainless barrel expands to twice it's original diameter (destroying the gun) and the carbon barrel is not harmed.

Actually, the stainless bolts are the ones that held up! They were loads stronger than the OEM head bolts (part number 92001-1445).

By the way, I just tried to put my last two 92001-1445s in there. One went in and torqued up to about 20ft-lbs, at which point I stopped. The other one started to feel funny around 19, so I backed it out. I saw the same necking you can see in the picture I posted of a broken one.

SO glad I backed it out. Gonna order two new bolts (and an extra). I'm not taking the nuts off, because I don't want to scrape off and put new Permatex on.

I know there has been disscussions on this before, the torque for the bolts is wrong even in the kawasaki feild manuel!! Trust me!! its like no more than 8 lb ft. I'm an Automotive Technition and I will tell you not the best bolt that size should be torqued to 22 lb ft. in aluminum. Do some research and you will find the correct torque.