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10.20 - Spark plugs replacement ( V12 XJ40) ( Win Dooley,  )

Changing the plugs on the V12 looks like a hassle compared to the 6's, but tt's really pretty easy .....

To change the spark plugs, cover fenders with protective cloth. Begin by removing the shroud that covers the valley of the V. Remove 4 crosspoint fasteners securing the shroud, and remove the shroud.

Set aside the air conditioning compressor. This is done by removing the tension from the serpentine belt and displacing the belt from the compressor. Remove and set aside the four #10 bolts securing the compressor to the engine. Move the compressor forward so that the 1A and 1B plugs can be reached. Clean the bolts and lubricate the threads with antiseize for reassembly.

Set aside the cruise control bellows by removing the two #11 nuts securing the assembly and move it out of the way.

Free the throttle pedestal. Remove the two arms that extend to the mechanism at the intake manifolds. These snap off. Remove the four #11 nuts securing the assembly. It can now be moved around to access 6A and 6B plugs.

All plugs can be reached with a 12 inch extension on the spark plug socket. A swivel was required along with the extension on 6A and 6B.

I used Autolite #103 gapped to 0.025". Lubricate the threads with anti sieze. Do not overtighten the new plugs. The 103 provided a smother idle compared to the Autolite Platinum used before

Allow 1.5 hours for this task.

If idle speed readjustment is required after plug replacement, idle speed is controlled by the #13 bolt on the Auxilliary Air Valve (AAV). The AAV is located at the rear of B bank (US driver's side). Set idle RPM as per placard on the fender.


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