Thanks Bill,
Now I see where you are coming from. Bear in mind that those documents were
all produced after the introduction of the swing spring
and after the camber compensator was discontinued. In other words, it was "the
only show in town", so there was nothing to compare
against. Still, it doesn't explain why anyone, particularly someone in the
Triumph Competition Department) would recommend replacing
the rotoflex with the swing spring. Apparently the factory was really proud of
the needless investment in R&D that yielded the swing
spring.
They tackled a problem (Wheel tuck) by reducing one of the superior traits of
the Spitfire, which of course is outstanding roll
stiffness. Kas' very simple and effective solution didn't take away from roll
stiffness but attacked the problem, not the symptom.
I am going to take this opportunity to ask Kas his opinion of the
recommendation to replace the rotoflex with the swing spring. I
think the factory did it to save bucks but if it is already there, I can't see
why anybody would recommend changing it to a less
effective suspension. Anyway, I'll report back with what he says.
Regards,
Joe
William Hooper wrote:
>
> 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.
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