|Steam comes out of the head bolt holes on a Turbo R with blown gaskets|
|Coolant leaking from head bolts is a sure sign of head gasket failure, and maybe more damage|
|A Bentley engine with heads removed (c) J E Robison Service|
|An assembled Bentley Turbo motor, vintage 1996 (c) J E Robison Service|
|Rolls-Royce Bentley V8 with 20 head studs on each side (c) J E Robison Service|
|Bentley Turbo - head gasket blown at the bottom on both cylinders (c) J E Robison Service|
|Bentley head stud with threads pulled (c) 2014 J E Robison Service|
I used to think these Bentley head gasket jobs were simple. Not anymore! It seems like every one we've seen in the past few years has had more complications than the one before. Most of these engines have one or more pulled studs and some have other damage.
|Head stud and insert (c) J E Robison Service|
|A repaired head stud (c) 2014 J E Robison Service|
The most common stud failures are on the top and bottom rows. That's lucky, because the center rows studs can't be fixed without stripping the block. If you fix studs, it's absolutely critical that you drill the repair holes straight. If the studs are even a little bit crooked the head won't go on! The photo below shows the alignment fixture we use to drill straight holes.
One engine this summer got hot enough in the front cylinder to melt the injector tip. What do you do then? A wise person would change all 8 injectors on a 20-year-old car, but that is several thousand dollars of parts. When the fuel rail is apart don't forget the other o-rings that you can't get at when the motor is together. Repair of these motors can get expensive fast. You don't want to ask how bad it can get because the answer is over $50,000 as of 2014.
Before you dismiss that number as crazy, consider these costs if you drive your Turbo Bentley until the engine overheats and seizes
- Rebuild long block engine after major failure - $35,000
- Replace melted injectors and rail parts - $3,000
- Replace water pump, radiator, coolant hoses and thermostat - $3,000
- Replace other heat-damaged parts - turbo, pipes, possibly catalyst - $3-6,000
- Labor for all this work - $10,000+
We also do a full valve job, to ensure the car runs as smooth as possible. I often see shops skip this step too, but why? If you can spend a few more hours here and get a smoother car, why would you not do that?
|Bentley cylinder head ready to install (c) J E Robison Service|
What's the typical repair consist of now?
- Remove heads, clean all parts, and check for damage. Always pull both heads, even if only one is blown. If you don't, the other side will fail soon after. We have learned that the hard way.
- Check the heads for cracks and warping, and do a full valve job with guides and seals.
- Check all the injectors and replace all fuel injection o rings.
- Replace the thermostat, belts, and other consumable parts.
- Use a fixture to test torque the head studs 20% tighter than stock and ensure they do not begin to give way when left overnight. Repair any that are marginal.
- Use a gauge to check block flatness and consider full overhaul if the warpage is more than .004
- Replace all the hard rubber hoses in the center engine area - this is your time to get at them easily.
- Look at the cylinder walls for signs of scraping. That could be evidence of piston damage. If you see this, the engine should be removed and the pistons pulled.
- Look at the oil, and sniff it. Is it burnt? Burnt oil is a very bad sign because it means the core of the motor got very hot.
- Look at the amount of warpage in the deck. If you have .003-.005 of warping (measured with a good straight edge) that’s probably ok. .010 of warping and you may have bigger problems that will necessitate engine removal. When the metal is warped at the top it may be warped at the bottom, and if the crank journals are out of true the engine will eventually fail.
Why do these engines fail?
That's an excellent question. Here's my theory. When the car is new the head bolts are torqued to around 50 foot-pounds. With 20 bolts per side, this adds up to many tons of clamping force on the gasket surface. This force is increased every time the engine gets hot, and it's relaxed when the motor cools down. When the motor is overheated the pressures skyrocket.
After a few such cycles the gasket gets squeezed a tiny bit thinner, and the torque on the bolts starts to drop. The result - lower clamping force on a cold engine. When the motor heats up, all is still well because the thermal expansion tightens everything up. But on a cold engine we have an incipient disaster. When the low clamping forces of a cold engine with relaxed torque come up against the high cylinder pressures of a turbo engine under throttle the result may be a blowout.
That is why Bentley Turbo head gaskets blow out on cold engines. Hot motors are much less at risk. It's one more good reason to warm your Turbo up thoroughly before you get into the throttle.
|Bentley engine - always check the desk surface for warpage (c) J E Robison Service|
|We use Copper-Cote to help seal the head gasket after a blowout. Reassembly of a Turbo R (c) Robison Service|
Applicability of this article:
The information in this article applies to all Bentley Turbo R, Continental R, Continental T, and Azure cars, from the late 1980s to the early 2000s. It's also mostly applicable to newer Bentley cars (Arnage, etc) with the 6.75L twin-turbo motor, though the teardown and reassembly of those engines may be more complicated and they are likely to have additional damage.
|Bentley Continental T (c) J E Robison Service|
|Bentley Azure (c) J E Robison Service|
|Bentley Turbo R (c) J E Robison Service, Springfield, MA, USA|
Give us a call at 413-785-1665 if you'd like to talk about a Rolls Royce or Bentley engine repair. We handle all aspects of engine service and rebuilding.
Robison Service has provided independent service, repair, and restoration for Rolls Royce and Bentley owners all over New England for over 25 years. Our company is an authorized Bosch Car Service Center. We also service Mercedes, Jaguar, Land Rover, Porsche, and MINI motorcars. We have flatbed transport throughout the region. We also offer pickup and delivery for cars in Springfield, Wilbraham, Longmeadow, Agawam, Westfield, Northampton, and Amherst.