Torque Cylinder Head

RW, 

A friend of mine who has a year 2019 914 in his aircraft had it over-heat and there was obvious damage. We tore it down and sent the parts to a well-known and respected Rotax Service Center here in the USA for inspection. The heads and cylinders did not pass the hardness test so they were replaced along with other damaged parts. However, this service center insisted we did not need to replace the head studs. I agree that the steel studs can take more heat than the surrounding aluminum parts, but I was under the impression that they should be replaced since they are stretched when torqued. Following their expert advice, we did not replace them, and all seems fine so far with about 50 hours since the repairs. What is your opinion? 

Hi Jeff

The internal studs are the ones that can't be reused.  The head studs do not have as much stress and they say you can reuse them.  Be very careful on the mid torque sequence, where you have to take them up to 30 NM, you may see the stud fail.  The way to know this is that the stud will not take the torque and may even drop some.  This is a sign that the stud is failing and will need replacement.  Generally if one starts to do this I personally would change all of them.  If it takes this 30NM you should be fine. 

Cheers

I apologize for not saying thank you sooner. I'm asking a new question.
I'm overhauling a 1998 80-hp 912. I tightened the cylinder heads exactly as shown in the photo at the beginning of my post.

Did I do it right or wrong?

Thanks for your input.

Alejandro Zapata

Spain