Frank:
I second the motion regarding buying bolts with rolled threads, instead =
of cutting them myself. When cutting, there is absolutely no way to =
produce a thread that does not have potential for failure.
-----Original Message-----
From: Paul Burr [SMTP:tigerpb@ids.net]
Sent: Monday, February 09, 1998 7:43 AM
To: Frank Marrone
Cc: tigers@autox.team.net
Subject: Re: Crossmember Bolt Tech Tip
Frank Marrone wrote:
>=20
> I have a reprint of an old Tiger Tales Shop Note that suggests the use =
of
> longer bolts for bolting the crossmember to the frame. The note says =
to
> use bolts that protrude far enough out of the threaded tube on the top =
side
> so a locking washer and nut can be used. This is supposed to reduce
> flexing of the threaded tube due to acceleration and braking forces. =
I
> think the idea is that cumulative flexing stresses can lead to fatigue
> failure of the threaded tubes(?).
>=20
> Is this something that should be considered? I'm rounding up hardware =
now
> to bolt the crossmember back up to the frame so now would be a =
convienient
> time for me to do this.
>=20
> If this is worth doing, where the hell do you find Grade5 or 8 bolts =
that
> have enough thread length to do this? I'm going to try to run a die =
down a
> Grade5 bolt today to see if I can make my own.
Frank: if I'm not mistaken, I was the author of that article. In
researching the fastners that Rootes used, it quckly became obvious that
the lower arm to X-member bolts were not standard items! I tried to run
a die up closer to the bolt head.(like you're thinking) but the grade 8
stuff is so hard that it ruined my consumer grade die. Not to mention
the nagging doubt that cutting it would weaken the point that would be
carrying most of the load on the front end.
I stumbled onto the solution in the Pegasus Racing Supplies catalog
1-800-688-6946 (pegasus@execpc.com) (email your snail mail address and
request a free catalog.)
They sell aircraft grade bolts. These are sold by "Grip Length". This is
the unthreaded, load bearing portion under the bolt head. You order the
bolt with just enougth length to grip and clear your fulcrum pin,
brackets and washers. Then you specify just enough thread length to fill
the hole in the crosmember.
This combo yeilds the ultimate in fastner strength. It's light years
beyond grade 8. They have a tensile strength of 125,000 psi and a shear
sterngth of 76,000 psi! When my lower fulcrum pin cracked in half, these
bolts didn't move or crack!
Despite all this, they really aren't costly-@ $3 each. At this price, it
makes no sense whatsoever to be carving up hardware store bolts trying
to make them fit!
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