General Maintenance: Tips for Replacing Spark Plugs
I recently replaced the spark plugs, so I thought I would document things I have learned over the years.
After the projects last winter I have been playing with different parameters to get the car running as well as possible. One area is fuel pressure. After trying two different stock Bosch (Lucas labeled) fuel pressure regulators, I have found that there is about a 1 psi pressure drop once they get hot. Until I get an air / fuel ratio gauge installed, I was running as rich as possible and checking AFR the old fashioned way, by looking at the condition of the spark plugs. Well…I obviously got too zealous in running rich and fouled the plugs so I needed to change them out. In the process, I decided to document changing out the spark plugs.
I find the most frustrating part of changing spark plugs is removing the wires from the plugs.
Don’t waste your money on these tools…they don’t work
Needle nose vice grips work, but are aggressive and I have ruined wires with them.
I highly recommend this tool. Part number 51410 from Lisle.
Makes it a lot easier. Still possible to separate the wire from the connector with these but the chances of success are much higher.
Very fouled spark plugs from running way too rich
NGK BPR6ES are generally considered the best plugs for the Jaguar V12. They need to be regapped to 0.035 in (for NA cars)
OK….there is some controversy about this step. Nowadays most plugs have the shiny silver coating on the threads and the manufacturers do not recommend using anti-seize when first installed. If you remove and re-install, the coating has worn off and it is recommended then. I’m old school here and want to protect the threads in the aluminum heads, so I always apply a small amount of anti-seize when installing.
This simple tool or a piece of fuel hose makes it easy to start engaging the threads in the head.
If using anti-seize its recommend to lower the installation torque by about 15%. I set the torque wrench to 185 in-lb’s.
Used a Q-tip to apply dielectric grease to the inside of the wire boot
As with most things on the Jaguar V12, access can be awkward, but this is a straightforward project and I am told much easier on our engines than the later HE V12’s.
