On 2/6/2014 10:18 AM, Bob Lowe wrote:

I use to look at the four fire-wall engine mounting bolts of
my plane and think, if I were doing this I sure would have used heavier
looking bolts. And as you may surmise, I should surely understand the
strength of a bolt to get anywhere with this. Even if I should buy a
'kit' I know that I would be tempted to use a better bolt.

Bob Lowe

Hi Bob,

Look, I have to say something that could be taken negatively, but I have
to say it. So, in the interest of safety and education consider this...


Bad idea.


Until you can calculate the loads imposed on a fastener, _don't_ make it
stronger. In fact, don't make any changes at all.

Two reasons off the top of my head...

One: consider the structure that the bolt penetrates. A Larger bolt
means a larger hole too. Sometimes that will be ok - but sometimes the
edge margin could be critical and enlarging the boat could weaker the
attach point. In trying to make the structure stronger you could
easily make it weaker!

Two: sometimes structures are designed to fail in a particular manner.
Making a connection stronger in the wrong place could defeat that
strategy and cause a much worse failure to occur.

And three: A proven design doesn't need to be stronger. If anything
it needs to be lighter!

Just looking at a detail (like a 747 engine mount?) one often wonders
how the engine can possibly stay on the wing. But it does, quite well.

It's all in the numbers.