I have two bits of paper with recommendation for replacement of the rotoflex
suspension with the swing rear spring suspension (and before going further,
remember that today opinions regarding the two designs may not be the same!
I then & still prefer the rotoflex supension for daily driving like a
lunatic on roadways, up & down the grassy parts near exit ramps, ripping
across medians, & the residential street gymkhana. On the track is always
something different, and of course, opinions, needs, & practices change over
time. This ain't 1980, & your mileage may vary.)
The first document is likely from Jaguar Rover Triumph; it's not on
letterhead & has no date, publication number or part number, but I've got it
in a notebook stuck between two JRT "Special Tuning Data" letters dated 1978
& 1980. Both the JRT Special Tuning Data notes & the "Swing Rear Spring
Conversion" page are folded only in the center, not 3 times as a letter, so
it's possible that they were all sent at the same time (around February 25
1980) from JRT in one 4x5 envelope, as a collection of current & older
technical memos. (Don't you love archaeology?)
---
"Swing Rear Spring Conversion
"Spitfire Mk I, II, III
"GT6 Mk I, II, III
"Owners of early Spitfier and GT6 models interested in improving the
handling will find that the best investment is the installation of the rear
"swing" spring", as fitted to the Mk IV & 1500 Spitfire models.
"The arrangement of swing axles and transverse leaf spring, used on early
GT6 and Spitfrie models, has an extremely hig roll center which under high
speed cornering conditions results in the wheels becoming cambered, with a
consequent loss of adhesion. The way to minimize this is to reduce the roll
stiffness of the suspension.
"On the later Spitfire (Mk IV and 1500), the Engineering Department modified
the Spitfire's transverse spring to cut its roll resistance by 75%. Only
the main leaf is clamped to the differential, so it can contribute to roll
stiffness. The other leaves are free to rock on their centers and simply
provide bump stiffness. The wheel spring assembly also has a higher
two-wheel bump rate, so the camber range under braking and acceleration is
considerably reduced. To compensate for loss of roll stiffness at the rear,
the front anti-roll bar was enlarged from 11/16" to 7/8".
"To install the new spring setup you will require: spring assembley 159640,
4 studs 131008, and 2 plugs PU 0804. The swing spring is mounted on 4 studs
as per the drawing on the next page, and the 2 remaining stud holes in the
axle casing are plugged to ensure that neither differential lubricant is
lost nor foreign matter enters the axle casing. These plugs should be
installed with the appropriate Loctite sealing compound. Alternatively, the
2 center studs can be tightened fully home in the axle casing and then cut
off flush with the casing. If, after installation of the swing spring, you
car has an oversteer characteristic, it is suggested that you replace the
original 11/16" front anti-roll bar with the 7/8" bar, 217033.
"We are sure that you will be delighted with the reults of this modification
as it will greatly improve the handling of your behicle and enhance the
subsequent pleasure you will derive from driving it.
(The pictures on page two are just reprints of the parts manual for the
Spitfire Mk IV and 1500 Swing rear Spring attachment, w/part numbers. Below
is a picture showing the non-swing spring attachment from the parts manual
for Spitfire Mk I, II and III.)
The next bit of documentation is the red British Leyland Competition
Preparation manual for GT6 and 2000, 2nd edition, by R. W. Kastner, Triumph
Competitions Manager British Leyland Motors, Inc. 2nd Edition revised 1977
by Mike Barratt, Competition Technical Advisor, British Leyland Motors, Inc.
"It is the policy of the Triumph Competition Departments, both in England
and the U.S., to constantly seek improvements in performance. As new or
revised technical data becomes available, sheets will be made available for
insertion into this book."
Page 23, "Rear Spring" section (in its entirety): "The stock rear spring
should be replaced with the latest swing type spring Part #159640, details
of installation are contained in the Competition DPT Bulletins. The spring
should be de-arched by a spring shop to 1" before installation and the
second leaf cut off at the point where it wraps around the eye. To prevent
it bottoming, the clamp bolts should be bushed with aluminum tube to contact
the spring leaves and prevent them from separating."
Also you can see that losing a leaf may be okay on the track, but won't be
pretty driving to the Circle K or across the state.
--------------
By the way, while excavating this stuff, I discovered with it a very nice
letter from Mr. Barratt on JRT letterhead of 2/25/1980. In it, he answers
some questions I'd asked about cylinder head thickness & the availability of
the very yummy-on-the-graph-looking JRT/BL GT-6 competition grind S2 cam,
for street/mild race application. (I musta had the engine tore down & at
the engine shop.) Here's the whole thing (minus salutations &
cordialities), in case anyone's ever wondered about these things:
"Please be advised that the GT-6 Competition Preparation Manual is in the
process of being updated to accomodate specifications that were made since
1968, as compression ratios range all the way from 9.5:1 to 7.4:1 on later
emission engines.
"However, the datum point is the 8.5:1 compression ration with a cylinder
head of 3.460. The only modifications that were made to the engine on later
models, was to achieve a lower compression ratio, was to cut the head
casting thicknes. Therefore, regardless of the original thickness of your
cylinder head, to achieve a compression ration of 10.25:1, it is still
neccessary to mill for a final thickness of 3.375. We trust that this
clarifies the cylinder head problems.
"Turning to the camshaft problem; the S2 camshaft as quoted is no longer
available due to the fact that we are experiencing difficulty in getting the
cam blands from the factory. We have been promised a supply of cam blanks
which have yet to materialize. When these become available, we will once
again be able to supply S2 cams.
"Meanwhile, we would suggest that you contact Iskenderian, Racing Cams,
16020 S. Broadway, Gardena, CA 90248, 213-770-0930, who can regrind you
existing cam to a specification which is very close to the S2, which they
call Z19 grind; which is suitable for competition and street use. The S5
camshaft is an all out racing cam and is in no way suitable for street use.
I don't know what changes if any were made to the GT-6 camshaft design as
the models were de-tuned for emissions control; the Competition manual seems
to be referenced to the GT-6, MkII & GT-6+.
Mine was a Mk III, and on this rebuild I remember trying to get hold of
Iskenderian, was unsuccessful for some reason (turnaround time to slow?),
and was referred to Reed Cams which had a mild regrind which was sort of
third choice but still close to an S2 reference & a noticeable improvement
for the GT-6 Mk III. I don't recall, but Iskenderian or JRT may have
referred me to Reed. I'm particular.
(June, 2000: "Hello, Isky?")
>From: Joe Curry <spitlist@gte.net>
>
>Bill,
>Which competition Preparation manual is that? I have had numerous EMAIL
>conversations with Kas while doing the re-release of his
>camber compensator and I got the distinct impression that he didn't feel
>really good about the design of the swing spring. He seems to
>convey that the camber compensator is a far better arrangement than the
>swing spring. I have the Mk1 through Mk3 Manual and of course
>the swing spring wasn't available at that time.
>
>I think the later competition preparation manuals were written by a
>different person than Kas. No flame intended, I'm just curious!
>
>Joe
>
>William Hooper wrote:
> >
> > Kas Kastner in his GT-6 competition preparation manual recommends
>replacing
> > the rotoflex rear suspension with the latest-model swing spring
>suspension.
> > He obviously likes the swing spring, & it's the one to have in
>competition.
> >
> > I like the rotoflex. It was the suspension on the first car I owned,
>which
> > I still have, & we understand each other. I changed over to the swing
> > spring once, but changed back. There's something fun & frisky in the
> > rotoflex; it matches the 2.0 GT-6 engine, which, as someone else here
>noted,
> > has a snappier personality than the 2.5.
> >
> > To be honest, both rear suspension designs are a little weird. You can
>have
> > large black rubber donuts, or a rear suspension spring that woggles
>around
> > in its mount on the differential. That's fine, it goes with the rest of
>the
> > car's personality. (Gas station mechanic about 1977 upon seeing the
> > Strombergs: "What do you have flying saucers under the hood for?")
>Don't
> > even start about the BPDWA.
> >
> > In case anyone has ever been curious: I once installed a swing spring &
> > left the rotoflex axle shafts in place also. The result was scarier
> > than can be described.
> >
> > ________________________________________________________________________
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