I am about to replace the wires and spark plugs on my v12 but I wanted advice as to whether I should clean the engine block before or after I change out the plugs.

Thoughts?

 

Before. You dont want anything to fall into the plug hole that could damage engine.

 

If you have never done this before, a few tips in case they are useful, many apologies if you knew all this:

• get an airline and blow out the spark plug wells and then vacuum them with a small nozzle. This gets out all the bits of dust and grit that accumulate. I would not use anything else, or clean anything else, however oily, as this has a VERY good chance of ruining some electrical bit that will drive you nuts to fix.
• it is VERY easy to crack the plug insulation when undoing them. Listen carefully and if you hear the dreaded 'ping', undo the plug very slowly one turn at a time, and vac, nozzle over the plug, each time you do one turn, and when nearly unscrewed use the airline again to be sure any loose bits are blown away. A loose piece of insulator will fall straight into the hole, reveal itself by a ticking noise on startup, and may get blown out of the exhaust , or may get embedded into a valve seat and ruin it.
• the plugs under the aircon compressor are very hard to get to. There is a special tool but if you do not have it, the belt must be loosened and the compressor unbolted and raised - which is why most V12s have never had their front two plugs regularly changed. It is just possible to undo the plug without the compressor being raised by finding a plug socket with a hexagonal outer and cutting it down at the plug-end. then it can be slipped over the plug and an open ended spanner used to turn the plug. Installation of the new one is the reverse, as they say.
• Although a pain to do, removing the throttle pedestal makes the rear plugs much easier to do, and more to the point, much easier to get the plug spanner on absolutely straight, thereby reducing the possibilities of the cracked insulator nightmare.

One of the many rites of passage!


Greg

 

As Greg said and,

ONE plug at a time. You dont wont more than ONE hole open to the engine at a time.

Then, when one plug is done, blow it all out again, then do the next one, and so on. Sounds overkill, but a piece of something down a plug hole that gives the "death tap" when started is worse.

Being a 6ltr, it MAY have the compact compressor as factory fit??. That compressor makes 1A and 1B quite easy to get at.

 

Did mine just a couple of weeks ago.
The compressor is fairly easy to move. Just four long bolts holding it in place. Removing those, and moving the compressor around just a bit is a big help. Also, a can of compressed air (available at any hardware or office supply store) works well if you don't have access to another source of compressed air.

 

As I replaced my plugs, I used a hoover to get all the grime out. Leaves, needles and co were all around the plugs. Still not totally clean but it is getting there

Oh, and don't try to remove the plugs with the AC-compressor in place...

 

Thanks to all your advice I was able to complete the plug and wire replacement this weekend. I did have to remove the AC compressor and throttle complex. It looks like 1B, 4A, 6A and 6B had not been changed as recently as the others. I understand why they are hard to get at!

Did a test drive after completing the work and everything thing appeared great (it was cool and raining).

However, this AM in traffic she overheated going straight past N. I quickly got out of the traffic and cooled her off a bit before getting home and popping the hood. No fans turning! I guess I did something to the wires that run the fans. Any idea how I screwed up and how to fix it?

Thanks in advance