Date: Thu, 17 Jun 2010 16:59:02 -0500
Reply-To: mcneely4@COX.NET
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dave Mcneely <mcneely4@COX.NET>
Subject: Re: seat belt replacement, tough anchor bolts
In-Reply-To: <4c1a8e50.1b73e50a.6e9e.ffffc37d@mx.google.com>
Content-Type: text/plain; charset=utf-8
could it be that M11x1.25 was VWs response to the requirement of 7/16x20 or nearest metric equivalent that John described? My camper is a 1991, and it had (still has in most positions) the bolts with 8.8 stamped on the head.
Sincerely, David McNeely
---- David Beierl <dbeierl@ATTGLOBAL.NET> wrote:
> At 04:08 PM 6/17/2010, John Reynolds wrote:
> >John -
> >Who has has been involved in testing and design of "few" seat belt
> >bolts for a few decades now.
>
> Dear John,
>
> Since when do UNF bolts come with grade 8.8 stamped on the bolt end?
>
> >I wrote:
> >>Bolt is M11x1.25 grade 8.8 (which grade most bolts in the Vanagon are).
> >>
> >>Starting torque was 50 N-m, about 37 lb-ft. Removal effort was low
> >>but very quickly increased to 15 and then 20 N-m as the slightly
> >>corroded end of the bolt entered the hole. The bolt was warm when
> >>it came out, reflecting the work done to remove it.
> >>
> >>Measured OD was .430" against a nominal 11 mm which is .433 (7/16 is .4375).
> >>
> >>More to come.
> >
> >The M11x1.25 bolt thread was chased with 7/16-20 (moderately
> >interesting pics to follow). A 7/16-20 hole was made in mild steel
> >(75% engagement depth) and tapped with a Craftsman carbon steel
> >tap. The bolt was tried in the hole and entered freely. It could
> >be spun in and out with great ease but did not feel sloppy.
> >
> >The bolt was then inserted to the same depth as the depth of the
> >hole in the Vanagon, and torqued to failure. At 70 N-m (~52 lb-ft)
> >the fastener pulled out of the steel. There was some thread
> >deformation and rounding over on the bolt, but the threads in the
> >steel were pulled out complete and could be unscrewed from the bolt.
> >
> >Conclusion: For this application it is acceptable and safe to use
> >the existing M11x1.25 grade 8.8 bolt in a hole that has been chased
> >with 7/16-20 tap, even though the thread forms are slightly
> >different and the tap is just a touch large. The VW-specified
> >nominal torque is 30 lb-ft. However an M-series grade 8.8 bolt
> >corresponds to a UN (Unified National) grade 5 bolt, with three
> >lines on the head. Using a grade UN grade 8 bolt will require more
> >tightening torque to avoid potential fatigue failure (remote-to-zero
> >possibility in this application) and the hole in the van might
> >possibly not be strong enough for the increased torque.
> >
> >
> >d
>
> Yours,
> David
--
David McNeely
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