Howdy,
I need a bolt recommendation...
The tow dolly I'm rebuilding has a single bolt that carries the load from
the tongue to the tilting dolly platform. This bolt gets all the weight
of the car. It goes through an inverted U section on the tilting
platform, with the boxed tongue in the middle. It doesn't clamp tight,
the inverted U section / tonque pivot around the bolt (it was kept in
place with a locknut).
The bolt that came out of it was a 5/8-11 grade 5 bolt. Even if I wanted
to, I can't reuse it, because the reason I'm rebuilding this thing is
because the inverted U on the frame frame the tongue bolts to cracked, and
now its thicker after reinforcement. In addition, the bolt's shoulder
didn't go all the way to the edge of the inverted U, so weight was being
carried on one side by the threaded portion of the bolt, not the shank.
There's wear on both sides, where the U/tongue loaded the bolt.
First question... Stick with grade 5 or use grade 8? The mount is in
double sheer, but there's no clamping happening here, its a strict bending
load with either end of the bolt supported. Essentially, the bolt is
being used as a 5/8" hitch pin.
Second... I assume I want a shoulder that goes all the way through, so
that load isn't being applied to the threaded area, right?
Third... Should I just use a hitch pin? Are there ratings on hitch pins
that might tell me what'll be safe for sure? Only thing with a hitch pin
is that I'd need to make darn sure the cotter pin or whatever couldn't
come out... If this thing fails, the tongue comes outta the dolly and
havoc ensues.
Outside to outside of the new reinforced U is 3.75". McMaster doesn't
quote the shoulder length exactly on the grade 5 & grade 8 hex bolts, they
quote it to 1.5" to 2"... That makes a difference if I'm trying to
minimize the extra shoulder sticking out past the load area.
Appreciate any thoughts. I'll make the call on safety, but I'd love to
get some opinions. At this point I'm leaning toward just using a hitch
pin and wiring closed the cotter pin, since this seems to be the exact
design criteria for them, though normally it'd be holding on tractor
implements that aren't going 75mph on the highway...
Mark
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