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Ignition Timing

Ignition Timing

My mechanic will adjust my carburettors next week, and he ask me for the
ignition timing-data. He tryed with the neon-lamp, spotted on the
fly-wheel, and he read 13 degr., he said. He do have no data-sheet for the
car (I think only 2 XK 120 where sold new in Norway) I told him could
contact the XK-lovers-group.
I should appreciate if someone could give me the data a mechanic need to do
a proper job adjusting the ignition.
- Martin Jacobsen

Set the contact breaker points to .012" and the sparking plugs to .022".
Turn the engine clockwise from the front until the #6 (front) piston is on
the compression stroke and 5 degrees (approx. 2 flywheel teeth) before top
dead center. Set the distributor micrometer adjustment to the centre of the
scale. Attach a voltmeter or 12v light between the distributor connection
and ground, and turn on the ignition. Rotate the distributor until the
light just comes on. Clamp the distributor. Then take the car out and drive
it. If it pings accelerating up a hill, retard it using the micrometer
adjustment and test again.

- Mike Eck
 '51 XK120 OTS
 '62 3.8 MKII

From memory, I believe 10 to 12 degrees before top dead center (BTDC) will
be fine!

The neon lamp approach is the preferred classic method - always works! This
should be done with the vacuum advance disconnected and plugged, with the
endine running at idle. Could be done with the vacuum line connected, but
this way we remove another variable!
- Larry Schear
Twin Cam, Inc.

On my car, eng. # NC8338-9, the factory SUPPLEMENT TO MK VII/XK120 SERVICE
MANUAL for MK IX called out 4 degrees for all Mk IXs -- but my AUTOBOOKS
702, XK120, 140, 150 MK 7, 8, 9 by Kenneth Ball (published 1973) gives far
more detailed info for all models. For my Mk IX, distributor # 40665.A
(which I have) and 9:1 head, timing is 5 degrees BTDC. On mine, timing
marks are set into front crankshaft damper (with pointer to set bolted in
above sump); scale is: 10/////////0 (lines are vertical). So I set the
pointer at the center line (5), timed it statically (with light hooked up
to distributor and points so it flashed when they opened), and dynamically
(with white chalk mark at center line ,5, stroboscopic timing light hooked
up to #6 cylinder, vacuum advance disconnected, and distributor clamp
loosened to turn it); set at 500 RPM (normal idle) and 1,000 RPM as a
check. No high-RPM/total advance test done (may do later), but spot on
after all this; runs perfectly, to 5,000 RPM -- no pings or other problems
-- just runs correctly!

Bruce tells me there are MANY variables re: timing -- MANY different
distributors were used, etc. My Kenneth Ball book calls out distributor #s,
timing for ALL models of XK120/140/150/VII/VIIM/IX; if anyone needs this
info, let me know at <jagmkix@cwo.com>.
- Larry Martz

If you have any questions or comments send e-mail to: ted@jag-lovers.org
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