[AT] Adventures with shear pins

[charlie hill]

Generally I agree John and I didn't mean to sound
like I was advising folks to otherwise.   However,
I've just had really bad luck with sheer bolts.
The first bush hog we ever owned was an Allis Chalmers
built one that daddy bought new with his D-10.
It was a 5' model and was actually too big for the tractor.
If you raised the lift it was a fair bet on which would come up
first the bush hog or the front end.  Still even being an
over powered gear box for the tractor, we couldn't keep the
factory sheer bolts in it and they never sheered when we hit
something.  You would just be mowing along in clean pasture
and the blades would stop turning.  Ok, you say, buy a lot of
sheer bolts and keep them on hand.  Well the problem was that
the factory Allis Chalmers sheer bolt was brass and it was
$13.50 in 1965 dollars.  On top of that the nearest dealer was
35 miles away.  So I started using grade 5 bolts.  It made no
difference.  I could still hit a stump without sheering the bolt
and it would still fail from wear after 40 or 50 hours of running time.

I've been through a few other brush cutters since that one and I have
never yet had a sheer bolt to sheer when I hit something regardless of
having a slip clutch or not.  In fact I've hit stuff so hard with that old 
D-10
that with the engine running at wide open throttle it shut off dead in it's
tracks,  Sheer pin never budged.  Not even the brass ones.

The best thing I've found is the slip clutch but they didn't have them back 
in the
old days or at least I didn't know about them until the 80's.   The only 
trouble
with slip clutches is that if you set them loose enough to do any good they 
tend
to slip when you don't want them too.  It gets down to how much risk to your
equipment you are willing to absorb in order to get maximum production.

Charlie


-----Original Message----- 
From: jtchall at nc.rr.com
Sent: Sunday, July 27, 2014 9:34 AM
To: Antique tractor email discussion group
Subject: Re: [AT] Adventures with shear pins


To each their own, but I'm going to run whatever grade shear bolt the
manufacturer built it for. Dad always taught me to buy a bushog by the HP
rating of the gearbox. The IH dealer he worked for sold Hardee, folks seemed
to have pretty good luck with them. Also, running stump jumpers is a great
idea as well.

We have three rotary mowers here. All are old. The one with the most hours
is a 3 blade Lilliston belt drive. Never been into the main gear box. No
slip clutch, just shear pin. Over the years we've broke a few spindles. The
belts probably slip and protect the gear box. No telling how many hours we
have ran it. Wore out one deck, bought a used one and when it wore out we
weled a thick sheet of steel over the whole deck.

Then we have a 2 blade Mohawk. It uses a slip clutch, but that’s not enough
to protect the outer gearboxes. I can't remember if the center gearbox has
ever been rebuilt, but those outer ones have a lot. We have to run it on a
tractor that is almost too small to lift it in order not to tear out a
gearbox. And this is just mowing grassy areas, not grinding up trees or
clearing undergrowth. It's one of the worst pieces of equipment ever to come
here.

Finally we have a single blade tow type Lilliston that is 50 years old. NO
holes in the deck believe it or not. No slip clutch, just shear pins. The
center gearbox has never been opened. My uncle used to make/maintain logging
roads with it and a 90 hp Deere. Just an amazing machine.

John Hall


_______________________________________________
AT mailing list
http://www.antique-tractor.com/mailman/listinfo/at