Top engine reassembly, stud replacement

Good day all, because of a leaky head gasket i striped the top engine (kz 1100). Now I am about to reassemble it with new seals-new gasket-new copper washer. when searching here I found some people say to replace the head engine bolt and their marching stud. But Why..... mine seems in great shape and I rely a lot on the service manual, witch doesn't say to replace them. Also so far I have not break or strip any bolt/nut on this old lady.

Any of you think it should be replace period.... or had any issues with the old hardware on reassembly? Any advice are welcome, I really don't want to miss some pertinent information before I put everything back together.

Valves are lapped, head was wrap a little but it is fixed now, everything else is within good tolerance. I believe it will be running strong again.

I can't wait to have it running again.
Good ride.

I'm still running my stock ones after 40 years.
Steve

If you are building a high performance engine, definitely replace them.

On a stock rebuild, the answer is maybe. If the engine has been apart multiple times, or if somebody constantly tightened the nuts to stop oil leaks, then it might be a good idea. The whole point of torquing the nuts is to create a certain amount of stretch in the studs. Picture some super strength rubber bands holding together all that constantly expanding, contracting, stretching aluminum. At some point in its life, each stud will reach its limit of stretch. This can lead to constant leakage, and under extreme stress, breakage.
On modern, high stress applications, some bolts are one use and done. For example, the rod big end bolts on the ZRX are never to be reused. On a stock rebuild of an engine that has not been abused, the factory studs are probably fine.

I replace stock type always I have had ones that look like new fail if you do not mind doing job a second time then reuse them but I will not.

Hi fullpepper,
We're running the original studs on all of our Z-1's. Unless the 1100 motor is significantly different, and and as long as you're running a basically stock motor, with stock compression and a straight head, you should be fine.

If there's any rust showing on the unthreaded part of the studs, now is a good time to apply some high-temp aluminum paint. They'll look great.

The first time the motor is run up to full operating temperature, thermal expansion will cause a small change (increase) in effective clamping force of the head fasteners. This is normal. When it cools that first time, thermal contraction causes that clamping force to relax a little, Also normal.

After you get everything reassembled, run the motor up to full operating temp once. Let it cool overnight. Stone cold. Re-torque all the head fasteners to spec. You might be surprised how much less torque you find than that which you applied during initial assembly. Then, go ride for another 30 yrs.

Good Ridin'
slmjim & Z1BEBE

This next time I will be replacing them as well as the crank bolts.
Steve

Stock motor you will probably be fine with reusing studs and nuts.
HD Studs and Nuts from APE are great and add to clamping power and are a good peace of mind item if you want to invest
in them . I run very high cylinder pressures being a High power turbo so every little trick I can do to hold the motor
together I am happy to invest in. Cheap insurance to prevent a failure or leak.
Dave

I've got the APE stuff in my little motor for the money I see no reason not to run them.
kzzone.com/studs.html

slmjim+Z1BEBE wrote: Hi fullpepper,
We're running the original studs on all of our Z-1's. Unless the 1100 motor is significantly different, and and as long as you're running a basically stock motor, with stock compression and a straight head, you should be fine.

If there's any rust showing on the unthreaded part of the studs, now is a good time to apply some high-temp aluminum paint. They'll look great.

The first time the motor is run up to full operating temperature, thermal expansion will cause a small change (increase) in effective clamping force of the head fasteners. This is normal. When it cools that first time, thermal contraction causes that clamping force to relax a little, Also normal.

After you get everything reassembled, run the motor up to full operating temp once. Let it cool overnight. Stone cold. Re-torque all the head fasteners to spec. You might be surprised how much less torque you find than that which you applied during initial assembly. Then, go ride for another 30 yrs.

Good Ridin'
slmjim & Z1BEBE

I was already thinking about that initial phenomenon. ..... heat expention/ contraction back to normal...... and retorqing all bolt. Thx for the nice advice. Thx to all also.

If your engine is stock the stock studs are fine (unless damaged of course). When tightening the head nuts the stud elongates slightly but this is within the elastic limit of the material. Release the torque and the stud returns back to the original length. It's this stretch that keeps the nut from spinning off on it's own. Tighten too much and you will exceed the elastic limit and plastically deform the material - NOT good. That's why you shouldn't torque the stock nuts much higher than the stock limit.

The only reason to use HD studs is if you want to run big compression pressure. High compression engine, blower, etc. Since the HD studs are thicker they require more torque to reach the elastic zone and stretch. When using studs like this I think it's mandatory to torque higher than the stock level. Using high clamp loads can put more stress on your gaskets. The base gasket in particular my fail prematurely unless you use a high quality gasket. The head gaskets typically have metal inside them so they are less particular about the extra pressure.