Good of you to mention an alternator tensioner failure. I'm designing an

alternator tensioner out of aluminum. Hopefully Paul can take a look at it,
and I'll

post a photo of it soon. It's a different design 3/4" inch square tube

with .125" walls, used strictly in compression.

Brian Trubee

Alternators are notorious for destroying brackets for some strange reason.
Chrome molly 4130 steel has a fatigue limit while aluminum does not. What

that means

is if the stress is below some value a 4130 steel bracket will last for
ever while an aluminum bracket will fail sooner or later. Since the

vibration

amplitude and frequency are unknown on an alternator bracket it is risky

to

use aluminum. If an aluminum bracket is over designed by a bunch it will

probably

last a long time. That is not to say it is not possible to design a weak
steel alternator bracket that can fail. The saving grace about brackets
is they are usually small and weigh less than a pound. So in general over
designing brackets does not add much to the overall firewall forward

weight.

For the same reason therefore it is best to make them out of heavier 4130

steel.

This prototype is made from angle iron. Most of the load is on
the pivot bolt closest to the V belt so there needs to be another small
clip added to hold the other end of the alternator. The adjusting strut
was cut down from the stock part.

Paul Lamar

Paul,
FWIW.
I'm no engineer, but one day I was talking to a chap at a local SAAA about a
bracket such as this and this discussion on the alternator bracket reminds
me of this discussion.
It would appear that a Company had a great deal of problem with this bracket
breaking ( frequency vibration) - they made bigger, better, thicker,
stronger brackets, but to no avail, they all broke within a short period of
time.
This Engineer suggested to go thinner, sure enough this bracket laster
forever.
The alternator bracket needs to be strong enough to be stiff, but if this
isn't good enough, you could use two thinner brackets with spacers. I
personally don't know if I could trust aluminium here!
But like I said, I'm no Engineer !

George (down under)

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