At 09:12 AM 8/8/96 -0600, you wrote:
> Tom,
> I am no engineer but have restored a lot of Tigers. This may be
>oversimplification but what would be wrong with just making the fulcrum pins
>without the reliefs then also making wider attaching brackets and the
>plate/pad that welds to the cross member with perhaps larger bolts as well.
>The pins would have to have some kind of locating tab but they would be
>added rather than reliefs cut in the pins. After installation they would
>still look very stock. Usually I am reinforcing and rewelding the
>crossmember anyway at the same time as the front end rebuilds so it does not
>seem like too much just to change the pads that attach the fulcrum pin at
>the same time. The old location would give the reference for rewelding the
>larger pads. Am I missing something here?
Dave,
I'd like to have a solution this simple also. If you get a chance, look
inside a crossmember to examine the structural components. What you'll find
is a pressed metal shell with a rectangular spacer plate on the outside, an
independent sheetmetal reinforcement plate, spot welded to the shell at each
mounting point and a rectangular, threaded nut plate, welded to the
reinforcing plate. This mounting assembly is functional primarily because
the fulcrum pin attachment bolts clamp the assemblage together. This is
what I consider a "skin stressed" design, an a damn good one considering the
vintage. This is also why its so dangerous when the skin or shell
surrounding the lower mounts begins to crack.
The internal nut plates are only 1.25" x 2.125" x .375" thick. Since the
original mounting holes are approximately 1.125" on center, there isn't much
room to move to the outside. In addition to the minimal size of the nut
plates, they are not mounted concentrically with the holes. I've considered
using larger bolts, holding the inside dimension between the bolts
(eccentric offset), but this does nothing for the original pin design
problem. The most common way to reduce this effect is to start with a
larger OD pin. I've done this, and it does increase the cross sectional
area, but it also increases the relative effect of the bolt notches and the
stress riser effect.
The whole nut plate assembly inside the crossmember could be changed, but
this would require either splitting the crossmember, or some other major
metal surgery and could easily lead to weld failures where the new pieces
attach to the shell. In any case, any solution I have devised in this area,
looks like a lot of money and work.
The replacement cross members I produce get internal reinforcements to
stiffen them and help carry the load from the nut plates. Even with the
rack clearance notch stampings removed, I wouldn't give much hope to the
ability to successfully modify the lower pin mounts.
I just haven't found any cheap easy fixes for any of these suspension
problems.
Tom Hall, modtiger@engravers.com
STOA (Sunbeam Tiger Owners Association)
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