Stress Relieving
 

I've got a two page summary of steps in rebuilding a 911 engine that Henry Watts wrote. Can't remember where I got it off the web, but anyway, he recommends stress relieving the case during rebuild. Specifically, as you are torquing the case nuts, head nuts, etc. I guess you would use a dead blow hammer or rubber mallet. This is not mentioned by Bruce A. or in Wayne's book. Anyone else do this or recommend it??

Stress is the life blood of all machines, especially complex engines.

It not only holds critical surfaces and objects together but those forces also come from the stress and strain of fasteners and their threaded surfaces.

Stress makes things move and flex, including the car and its driver.

Years ago while apprenticing I have seen old school engine rebuilders smack the heads of bolts with small hammers during torquing sequences to relieve any abnormal stresses in the assembly as the loads were increased.

My apprenticeship in the mechanical arts has been added to by my degree in aerospace engineering so I can appreciate the wisdom in some of the old techniques that I have seen that are not included in many formal texts of how machines are made and put together.

I must also add that most precision machinery will go together in a way where the issues to be concerned about regarding the proper stressing and alignment of components can not be addressed with an impact tool, just attention to detail.

I am planning on getting Wayne's book to get all the hot tips on how to put a 911/930 motor together that I am not intimately familiar with, for example sealing choices and assembly order.

With the exception of a few taps on some critical fasteners during the torquing sequence I see nothing in a 911 engine assembly that would benefit from a hammer tap more than it will careful attention to component assembly.

I think that the engine expands and contracts way too much to make this method of stress-relieving useful. I haven't read the article that you mention, but I am aware of what you are talking about. The trouble is, that you need to adjust or relieve the engine case when it is warm (doesn't really help you too much when it's cold). There is no reasonable method to do this, especially on an air cooled engine that expands quite a bit when hot.

If you can send me a link to that article, I would like to read it though - it may be an interesting read...

-Wayne