Abstract: In the interest of overall safety in the Tiger Marque, the
following technical information related to suspension component failures is
submitted. Permission is granted in advance to club editors to reproduce
all, or excerpts from this document.
From some of the responses received, I may have done a poor job of
explaining myself in my first post on the subject of Tiger suspension
component failures, and maybe I jumped on Paul harder than I should have,
for that I apologize. I do not condone and certainly did not mean in any
way to imply that faulty components are acceptable or should be sold,
particularly those related to safe operation of a vehicle. As a small
business owner, I guess I tend to get up tight when someone expresses the
suggestion of suing someone before ever exploring the other options available.
One of the situations I was attempting to explain is that ALL Tiger owners
have an increased risk with the lower pins (and other suspension components)
because many of them have reached or exceeded the actual design life and the
fatigue failure rate of these components is growing. We in STOA have not
seen a mechanical failure problem related to the lower ball joints from Q-H.
They may have other problems as are related later in this document, but
total mechanical failure has not been seen.
The basic fulcrum pin design problem was initiated by the Sunbeam, probably
in the 50's. The problem pertains to the bolt notches placed in the fulcrum
pins to locate the lower A-arms in relationship to the crossmember. When
Sunbeam created this design, I seriously doubt that they allowed for the
stress loads placed by a high performance small block V-8 coupled with high
performance tires. The fact that they have lasted as long as they have is
perhaps a minor miracle. The notches happen to occur at the points of
maximum bending stress. The notching has the effect of producing local
stress risers which amplify or multiply the stress in that area. Another
stress riser occurs at the change in diameter or cross-section, where the
bushing assemblies butt up against the larger central pin diameter. These
high stress areas are the two typical points of failure for these pins.
The original (OEM) fulcrum pins began to fail and break due to possible over
stress and fatigue cycle failures about 12 to 15 years ago. Rick and other
suppliers had run out of OEM supplies about that time. Some new pins were
obtained from Quinton-Hazel (Q-H) (a British manufacturer of ball joints and
other suspension components). Several of the Q-H pins failed at the bolt
reliefs within the first couple of years of service. As a Mechanical
Engineer, when I saw the failed pins, the reason was obvious. Instead of
milling the locating bolt reliefs onto the pins, the Q-H design had them
turned in a lathe. This produced a significant reduction in cross section
and a major increase in the stress riser effect. Rick pulled what he had in
stock and scrapped them. This was in about the 1983 to 1987 time frame.
Reports of problems ended shortly thereafter and have been non-existant for
over 7 years. Rick did not have a computer data base at the time he sold
these Q-H fulcrum pins, but is currently searching several thousand old
invoice records by hand, to attempt to identify any unknown buyers and make
them aware of this potential problem. He is also going to submit notices to
the Tiger club newsletter editors to advise people how to identify the Q-H
design fulcrum pins.
One of the interesting things about the failure of the fulcrum pins
(regardless of manufacture) is that they have always broken at low speed, in
fact the most frequent breakage occurs when someone is backing up into a
parking space, with the steering at its limits. I relate this failure mode
to the increased forces of reverse travel with Toe and Ackerman settings.
Most of the original suspension components including the ball joints,
steering rack, and possibly the fulcrum pins, were originally manufactured
by Engineering Products in Clevedon, Somerset, England. All of their parts
were of fairly high quality but the company no longer exists. This means
that the engineering drawings and specifications are no longer available as
a starting point of reference to provide information on materials,
manufacturing specifications and heat treatment requirements, which are
critical to the pins service capability. As a result, some manner of after
market manufacture must be used.
Rick contacted Moog ( a well known US manufacturer of suspension components)
with a request to manufacture replacement lower ball joints. They refused
to bid on this project explaining that tooling costs would be excessive.
They recommended Q-H, their British counterpart. In a related safety
question, Q-H denies the problems with their current lower ball joint
design. They ship to Rick and other suppliers with a Nylock nut. Rick
tosses this nut, drills a new hole and installs a castellated nut and cotter
key. I had one of their Nylock nuts unscrew on my daughters Alpine, and
drop an A-arm. Their current design eliminates the OEM original copper
plating which prevented rust. Rusty ball joints tend to unscrew the nut
with the spindle. If you don't have cotter keys on your lower ball joints,
I'd advise you to drill the studs and install them. I also recommend marine
grease in the Q-H ball joints. The extra rust inhibiters in the marine
grease will help prevent rust and should increase ball joint life.
A more recent problem has occurred with upper ball joints. Most of the
replacement ball joints sold since the OEM inventory was used up have been
manufactured by Q-H. These ball joints are a press fit into the upper
A-arm, with a circlip to prevent them from popping back out. The Q-H upper
ball joints were manufactured with approximately a 0.015" increased OD to
insure a tight press fit. The Q-H upper joints are no longer available, and
the only supplier is Sidem of Belgium. Unfortunately, Their design only
provides 0.004" OD increase over the OEM design. This may result in an
excessively loose fit if the new Sidem ball joints are used to replace Q-H
joints. The Sidem joints should only be used to replace OEM ball joints.
Q-H has demanded a minimum order quantity of 1,000 ball joints to initiate
remanufacture, which makes the potential unit price prohibitive.
Because of my own personal technical interest, I attempted to have several
of the OEM suspension components tested by a metallurgist associated with a
fastener manufacturer of U.S. national reputation. This occurred shortly
after SUNI I. The intent was to identify as much as possible the alloys and
heat treatment used by the OEM for these components. Three years later, due
essentially to politics and bad feelings associated with the development and
creation of SUNI II, the package of components was returned, untouched.
This kind of testing work is expensive, but I feel that it is necessary as a
starting point to the development of any replacement design. From that
point, the design process has to address all of the known problems to assure
that its at least as good as the OEM part and I feel that it should be
further refined to make it "better" to account for the currently anticipated
loadings in the Tiger application. I have had many discussions related to
this design process and the responses always come down in two groups. The
first group won't accept anything different than the "stock" design, 'cause
that's their orientation. The second group wants to minimize or eliminate
the OEM problems and use modern materials including urethane bushings, and
currently available ball joints to enhance the "total" design, an perhaps
make it more roadworthy.
I have my own preliminary concepts for designs to meet these two diverse
objectives. To cover the "stock" design, and protect against the effects of
sudden failure, the two stamped retainers on each A-arm would be replaced
with a single U shaped channel running the full length of the major diameter
of the pin. The inside of the U would be a snug fit for the pin diameter
and the bolts would pass through holes in the walls. This would serve three
purposes. First it replaces the relatively weak retainer stampings with a
stronger component. Second, the channel provides mechanical support for the
fulcrum pin and spreads the load out to reduce stresses. And finally, the
channel provides a capture function in that if the fulcrum pin breaks in the
bolt relief area, it is retained in position by the channel. This design
provides no protection for the second known failure point, and will probably
increase the stress at the change in diameter at the bushing surfaces. But
it does fit the "stock" system.
The second concept involves replacing the fulcrum pin with a piece of
substantially larger cross section, primarily a rectangular bar with the
four mounting holes to attach it to the crossmember. Because this new pin
cross section exceeds the diameter of the bushing holes in the A-arms, it
would seem most appropriate to use "bolts" from the outside of each bushing
threaded into axial holes in the new center bar. The larger cross section
would be sufficient to negate the stress risers at the four mounting holes,
and the "bolts" could be custom sized to provide more strength, and allow
the adaptation of urethane bushings.
This is where a significant level of agreement and funding is needed.
Considering the combined resources of the 5 to 10 individuals,
(manufacturers?) who make up the entire "Sunbeam Replacement Industry", I
don't see this happening anytime soon without financial underwriting help
from the clubs.
I certainly sympathize with Paul's anger and financial loss, but many more
of you could well experience the same problem or worse, if something isn't
done to arrest these growing problems.
Tom Hall, modtiger@engravers.com
STOA (Sunbeam Tiger Owners Association)
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