I see how easy the front seal would be, but the rear one would need part of the shaft dissassembled first?
Shamelessly copied this long piece from v12 forum is an explanation of throttle setup by Roger Bywater from a thread started by Sean Straw about 20 years ago. I also saw in that forum that the screws that hold the discs in place are split and expandable at their rear side, and that the clearance is desired top, bottom, and sides.
The following comes from Roger Bywater:
I donât advocate setting the throttles to anything other than 0.002"
clearance in any circumstances. Tighter than that and they are likely to
jam when the engine cools off. Wider than that can cause difficulty getting
the idle speed low enough. The clearance was changed for that reason from
0.004" used on early development cars shortly before D Jetronic EFI was
introduced. As on many EFI engines the idle air system is intended to
supply all the airflow at idle and any flow through the throttles is
negligible so any attempt to measure it is likely to be futile. In any
event the usual deposit build up, especially on B bank because of the
breather, will close up anything but a large gap around the throttle edge
over a period of time.On D Jetronic cars the balance pipe system is a bit too small where it
connects under the plenums so it is particularly important that the
throttles move in unison through the entire movement and any imbalance in
the linkage at idle can make this difficult to achieve. When the throttles
are correctly set to start opening simultaneously (with both set to the
same clearance) and reach the full throttle stop together, it follows that
the intermediate motion will also be reasonably synchronised.Actually the shortcomings of an undersize balance system are not so much at
idle and light load, because there is plenty of vacuum to draw a relatively
small amount of air through, so any difference of depression between banks
would not amount to much. More important is the effect at part throttle,
say 5 - 10" Hg depression, where a restricted balance system suffers far
more and can easily permit a considerable pressure difference to exist
between banks if the throttles are out of phase.Because the pressure sensor signal is taken from the centre of a pipe
joining the two plenums it will average any discrepancy so with any
imbalance one bank would be rich and the other weak. Hence the importance
of throttle balance in all conditions.Those D Jetronic engines are getting a bit long in the tooth now and with
general deterioration of injectors, valves and the engine generally I can
understand that it may sometimes seem expedient to open up one throttle
slightly to improve the idle quality. However if the engine cannot be made
to idle satisfactorily using the normal procedure then something is
fundamentally wrong and resorting to a differential throttle setting is
really a case of adding a fault to cure a fault, which is never a good
principle.Even from new there could be a measurable spread between individual
cylinders as is the case with just about all engines. Typically there will
always be some variation in idle CO emission of maybe 0.25 - 0.75 % between
banks and B bank tends to produce higher HC emissions (noticeable in a
proper laboratory emission test but not so obvious at idle) as a result of
the way the pistons rock around TDC.The balance pipe on the D Jetronic cars was known to be inadequate but was
Jaguarâs first attempt at an EFI engine during a time that was clouded by
political and financial difficulties so I donât think it would be fair to
judge the error too harshly. Similarly the double fuel rail was something
that I think Bosch said was necessary to obtain equality of flow to all
injectors. I personally did some tests with a prototype single loop rail in
about 1976 which disproved this.I also remember that Bosch were nervous about injector life because of the
suspected high underbonnet temperatures, yet I donât know of a single case
of injector failure other than from a sensitivity to contaminated fuel,
causing jamming due to the unforgiving tight clearance around the pintle
assembly. Later injectors used on the HE are much more tolerant in this
respect.These components would all be classed as âemission relatedâ so unless there
was some sort of crisis there was no question of making changes to a
specification which was fully certified, and in full scale production,
because of all the proving that would be necessary.The single loop rail and larger balance pipe arrived with all the updates
which coincided with the 10:1 compression engine in 1980. Unfortunately the
slightest fuel seepage would collect in the middle of the vee creating a
fire hazard which led to the later recalls and change to the square fuel
rail. In fact the twin rail D Jetronic system probably leaked more than any
other but didnât seem to cause much of a problem, perhaps because vapour
didnât collect in the centre of the vee in the same way.The following is the throttle setting procedure we provide with the
instructions for our conversions. On reflection perhaps I should make an
addition of pointing out that the centre pedestal bearings must be in good
order because excessive movement there would make proper throttle balance
difficult to achieve. Also the centralising and setting of the throttle
clearances is more easily performed with them removed from the vehicle.V12 JAGUAR THROTTLE LINKAGE ALIGNMENT.
The early injected version of the V12 built from 1976-80 with a Lucas
variant of the well tried Bosch D Jetronic injection system was
particularly critical about having the throttle linkage correctly adjusted.
The reason was that the balance pipe arrangement connecting the 2 inlet
manifolds was rather inadequate and was unable to equalise any significant
difference of pressure between them, bank to bank manifold pressure
differences of 0.05 bar (1.5" Hg) being certainly possible. Because the
injection system sensed engine load from a point of average pressure, such
an imbalance would cause one bank of cylinders to have over-rich fueling
whilst the other would be too weak, with obvious adverse effects on both
performance and economy. The multiplicity of links and bell cranks make it
quite possible for one throttle to open at a measurably different rate to
the other or for one or both to not reach the full throttle position at
all. Quite a number of cars must have spent their entire lives in this
state.The problem was largely rectified with the introduction of Lucas Digital
Injection in 1980 when a much larger balance pipe attached directly to the
rear of the plenums was adopted. The rare 10:1 compression engines made for
just one year and the subsequent HE versions were therefore much less fussy
about the throttle linkage however it is still good practice to ensure that
the mechanism is correctly adjusted if these engines are to perform at
their best. There is also a possibility that misalignment will cause the
voltage signal from the throttle potentiometer to be out of phase with the
throttle movement - not usually a problem but our Super Enhanced ECU can
then receive inaccurate data about the throttle position which may
adversely affect its performance.The following notes describe a procedure to set the linkage correctly.
- A (Early D Jetronic Cars 1976-80). Use a resistance meter to check that
the throttle switch, mounted under the throttle quadrant at the rear centre
of the engine is adjusted so that contacts 17, 12 go open circuit as the
throttle quadrant is moved away from its stop by approx 0.25 mm (0.050").
Adjust the switch position if necessary via the two clamping screws.- B (Digital EFI Cars 1980 on). Use a digital voltmeter to check that the
throttle potentiometer voltage at the closed throttle position reads 0.32
(+ or - 0.2) volts with ignition on and engine not running. This can be
measured on the red lead coming from the potentiometer which is located
under the throttle quadrant in the rear centre of the engine. Adjustment is
via the three clamping screws.- Release the two main pushrods (1) taking motion from the throttle
quadrant out to the throttle linkages.- Ensure that the throttles are accurately centred in their bores and
that the clearance is 0.002" (0.05 mm) at top and bottom (2) when closed
against the throttle stop screw (3) on the throttle body. Any greater or
lesser clearance must be rectified. Wipe any deposits away before
measurement and make adjustments at the screw as necessary. Large Bore
throttles supplied by us will always be set to the correct clearance and
will not require attention. The throttle stop screws should not be altered
again from this setting under any circumstances.- Check that all spindle bearings (4) in the linkage are in sound
condition without excessive side play including the nitrile bushes (5)
supporting the rearmost ends of the throttle spindles in the manifold end
plates. Renew any with more than minimal side movement - all are available
from Jaguar.- Check that the bell cranks (6), attached by a link arm (7) to each
throttle, just make contact with the fixed stops (8) on the manifold end
plate at the closed throttle position with negligible free play to the
throttle spindle. If not release the screw clamping the lower arm (9) to
the throttle spindle and adjust as necessary.- Refit the main pushrods and check that both throttles commence opening
together as the centre quadrant rotates 3 - 4 mm from the closed stop. Also
check that both throttles reach their respective fully open stops (actually
the side of the manifold plenum casting) simultaneously. Adjust the rod
lengths if necessary leaving some free play to allow for expansion of the
engine as it warms up.- Check that the quadrant also reaches the fully open stop at the same
time as the throttles. Also ensure that the kick-down switch closes with
further movement of the accelerator pedal. Note that XJS accelerator pedals
can sag towards the toe board so that kick down and full throttle movement
can be lost. This can be rectified by simply pulling the pedal arm as
necessary.- Start the engine and let it run to fully warm then recheck the movement
of the throttles and linkages. Expansion of the engine as it warms up takes
up most of the lost motion in the linkages and it may be necessary to
re-adjust the main pushrods.Roger Bywater / AJ6 Engineering.
â http://jaguar.professional.org/
Sean Straw '88 Jaguar XJSC 5.3L V12 (LHD) âBlack Catâ 63K
Marin County, California '85 Jaguar XJS 5.3L V12 (LHD) âBad Kittyâ 210K
'69 Buick GranSport 455 V8 324K
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