According to DerbyDad03 :
On Nov 30, 1:55 pm, (Chris Lewis) wrote:

Despite what others say, it should be able to stop momentarily without
destroying anything. I hit lots of things (rather rough ground in
places), and I've never had any damage (except for the blade getting
dinged of course).

Can you slacken off the belt a bit so it'll slip? Maybe it's too tight.

Good point. Shouldn't there be a sheer pin or key that would give
before a pully would strip out?

Normally, they use shear pins or keys on shafts that are gear/chain/direct
drive, so if you have an abrupt stoppage, you don't damage the engine or
transmission or gears. With belt driven components, they tend to rely on
belt slip for protection.

My Cub Cadet, for example, has a shear pin on the driveshaft between
the engine and the (hydraulic) transmission.

In contrast, the Cadet's attached equipment (mower deck, snow blower etc)
are belt driven, and have (at least) two slip points: the first one being
one or more belts (there are two belts between the PTO pulley and side
blades). The second being the PTO engagement clutch.

They don't necessarily slip much - if I run the blower into a
snowbank that's too much for the 12HP engine, the engine _will_ stall.
However, it takes several revolutions with loud squealing from the belts.
At least it's not instantaneously - which could do damage.

Cadets are built _tough_. This thing is from the early 70's, and
I use it almost like a bush hog at times. It had the bearing on the
main cutter blade wear out, the two idler pulleys that feed the
mower deck have destroyed their bearings twice each, and I've had
to replace the main mower belt several times (this belt is rather
fussy. Standard V belts aren't deep enough, and I screwed up once
and got too big a pulley which caused the belt to rub). The mower
deck has had to be unbent once. Aside from that...

On the Cadet, the side blades (it has three) are run by a long
belt (never replaced that I know of) from the center pulley, and
tensioned with a idler pulley on a spring.

In the OP's case, I'd:

1) Make sure that the deck isn't bent/distorted especially on the
side of the blade that destroys its spindles. It could be getting
restricted at the blade tip and very subject to jamming, or perhaps
the spindle mount is bent out of plane with the others.

2) See if he can slacken the belt a bit.

3) If it has a slippable engagement clutch, see about backing it
off slightly. Only slightly, otherwise he'll burn it out. You
only want it to slip on a stall.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.