<VV> oil filter and alternator mount bolts...

[Kirby Smith]

Interesting.  I think this implies that the aluminum also deforms, as it 
was my understanding that only 3 threads are normally actually engaged 
in threaded fasteners (at least for steel on steel).  So I'm imagining 
that the aluminum deforms until a sufficient number of threads are 
engaged to make the engagement area larger than the root area of the 
bolt.  Then the bolt becomes the weak link.

Independent of my imaginings, however, isn't the real question whether 
the strength of a bolt is sufficient for its purpose, i.e., holding the 
alternator down against g loads and resisting turning moments and shear 
from the fan belt tension?  Or, given that the bolts are supposed to be 
torqued, isn't the question whether the bolts are sufficiently strong 
for the specified torque?

kirby

JVHRoberts at aol.com wrote:
> You will, in fact, break the bolt long before you pull the threads from 
> the aluminum. This isn't determined by the material strength, but by the 
> thread engagement. Rule of thumb for aluminum using steel bolts is to 
> make the threaded portion at least twice as long as the major diameter 
> of the threads. On Corvair engines, the threaded holes have even more 
> thread engagement than this. And if the holes are in good shape and the 
> bolts are the right length, the bolts WILL yield before the threads do.
>  
>  
> In a message dated 7/31/2005 11:46:32 AM Eastern Standard Time, 
> kirbyasmith at gwi.net writes:
> 
>     Aren't these bolts threaded into aluminum?  (Sorry, but its been a
>     while
>     shice I built my motor.)  I'd be surprised if the aluminum is higher
>     tensile strength than any reputable 18-8 stainless bolt, even grade 2.
> 
>     kirby
> 
> 
>     JVHRoberts at aol.com wrote:
>      > 
>      > I would agree, except get Grade 5, and nothing less. SS bolts
>     tend to be 
>      > Grade 4 at best.
>      > Grade 5 have three lines on the head. Typical hardware  store
>     stuff is Grade
>      > 2, and may stretch at the required torque. 
> 
>