The mileage was 77k when the gaskets blew-the vehicle is a 1996 Mk4 facelift model with the Zytek injection system. I'm not sure why the gaskets blew but I know it's happened to other turbo R's & I've noticed that many of them are the Mk4 models with the more powerful & torquey Zytek injection system-maybe there's a connection?
I took the heads off myself & it's a massive job as there's so much stuff to remove from the top of the engine. It's not too difficult though, as there's no complex overhead cams & timing belts/chains to sort out-just a big, simple pushrod overhead valve V8 with no complex alignment procedures. You do need a good selection of tools though, as access to some of the bolts around the engine is limited so you need a comprehensive socket set with extension bars/universal joints & a good selection of spanners.
After removing the heads, the drivers's side gasket was clearly breached between the flame ring & a coolant hole on the second cylinder, which explained the cooling system pressurising & the misfire at start-up. The flame rings on the other cylinders were weakening & cracking as well, and across all 8 cylinders on both gaskets the flame rings had weakened in the area directly below the spark plugs-at the exhaust manifold side.
I assume this is because the temperature & pressure in this part of the combustion chamber are highest as this is where the ignition flame front starts, at the spark plug.
After looking around online, there was another owner with a Mk4 Turbo R which had blown it's head gaskets in exactly the same place-the guy had taken the car to a garage to be fixed & was presented with a bill for £6519, of which the biggest part was the labour charge.
This is why I did the job myself
The other guy had a photo show of each stage of the repair, showing the original blown gaskets-his blew at 65k miles. He wrote it up & posted it on the net under the name of Jon Honeyball. You can view the article at: http://jonhoneyball.livejournal.com/13325.html
It may be that the Mk4 Turbo R's with their extra power & torque are pushing the head gaskets to their limits & they need to be stronger, with wider flame rings etc. Way back in 2001 a mechanic posted on a forum that his garage had seen 5 turbo R's in for blown head gaskets, all with less than 50k miles on the clock. He made the comment that Bentley & the dealers stonewalled the issue...
To sum up, if you are considering buying a Turbo R-especially the Mk4 Zytek models for the 1996 model year onwards, treat any misfires from cold on the test drive with great suspicion. It's usually the first sign that the head gaskets are weakening. As the gaskets weaken further, the engine misfires on hot starts & pressurises the cooling system, causing rapid overheating & the heater to suddenly blow cold air.
Whatever the seller says, it's probably not just a spark plug or ignition lead, and they may be trying to pass the car on quickly before the gaskets blow completely-leaving you to pick up a huge bill, and I do mean huge. The parts themselves are not terribly expensive-it's just the labour charges that send the final bill sky-high.
I've been doing car repairs for 25 years so I was quite happy to do the job myself-it was actually quite enjoyable & a job to be done at a steady pace over 2-3 weeks. I'm in the final stages of re-assembling the very top of the engine & I took the opportunity to clean everything up during the overhaul-which added a few days
I do love my Bentley, but I realised that you have to fit into one of the following 3 categories to consider owning one without getting your fingers badly burnt:
You must either be:
2) Good with tools & have lots of them
3) Lucky-as in a generally lucky person who gets the best job & the prettiest
women, always backs the right horse & has been lucky all their life.