We are often asked what goes into rebuilding one of the V8 engines from Crewe. These are the motors that powered Bentley and Rolls-Royce motorcars from 1965 through the separation of the companies in 2003. A derivative of this engine is still used in some Bentley models.
You might wonder why these motors would need rebuilding, given that they power what are arguably the finest cars in the world. Would they really wear out? The short answer is, they seldom if ever "wear out" but they still succumb to corrosion when cooling systems are neglected. Crankcases become warped and damaged by overheating when thermostats or hoses fail, and they are driven anyway. Older engines may become clogged from sludge after years of neglect or low quality motor oil.
When that happens the engine comes out, and comes apart:
The designers of these motors built in what safeguards they could, but that only goes so far. In this pair of photos you can see a new thermostat and one that failed. When the thermostatic element fails to open in most cars the engine simply overheats. In a Crewe-built motor there are soft metal plugs that melt at about 250 degrees if the main thermostat fails to open. These plugs allow some coolant flow and hopefully preserve the engine. By comparing the two photos you can see the action of the safety plugs.
Good as this idea was, it does not provide 100% protection. In a normal thermostat the up and down movement of the center element also regulates flow of coolant through the motor. In a failed thermostat the melted plugs pass some coolant but the flow is uneven, from the front of the engine to the rear. When you ignore a melted thermostat, and then drive one of these engines fast, pistons can melt and seize in the bores, like this one:
The scuff marks on the side are where the piston got so hot it jammed in the cylinder bore, ruining both. Here is what the cylinder looked like:
Sometimes damage like that can be cleaned up with a hone, and a new piston installed. The engine's designers allowed for .004 inch clearance between piston and cylinder, so you may be able to hone away the scuff and fit a slightly bigger piston in that one spot. It all depends on whether the cylinders are still round. To determine that we use specialized measuring tools:
The thing we look for is out-of round. In this particular engine we found warpage of .007 inch, where the limit is just .001. If we had assembled the motor with that degree of warping it would have burned lots of oil because the piston rings could not seal properly. It also would have been at risk for head gasket and other failures down the road.
Failure to check details like this is one reason "cheap" engine overhauls often don't last.
When you find warping in a cylinder the only cure is to take the motor out of the car, remove the cylinder liners, and fit new ones that are not warped. At the same time, the rest of the engine must be checked for heat warping.
This is a block and liners, removed:
When the block is stripped and cleaned we look for another problem in these motors - corrosion. Here is a view into the block after the liner was removed.
More and more, we see the metal in there dissolved by corrosion. When the metal is corroded the gaskets that seal the liners against coolant or oil leakage can't hold, and the engine will leak irreparably. If that happens the block will have to be welded up or replaced - a big job or a big expense.
The final thing we look at are the crank, rods, and other internal moving parts. Are are checked for wear, straightness, and cracking.
We turn to the cylinder heads, which were removed early on. We look for corrosion or heat warping, and repair that as needed. Here's an example of a corroded spot on a cylinder head. IN extreme cases we fill that corrosion with metal from a welder. Then we smooth the whole surface on a milling machine to get the surface you see in the lower photo, true within a few ten-thousandths of an inch, and free of cracks and flaws.
The valves are removes. Seats are redone and valves recut. Springs are tested and replaced if weak, and new seals are fitted. Older motors did not have valve seals at all, but we normally fit them to reduce oil consumption and bring them closer to modern spec.
One of the decisions we need to make before assembly is whether to refinish all the parts to new spec, in addition to the mechanical repairs. These parts have been refinished with plating, powder coat paint, and other processes to be like new again:
At first blush you'd think everyone would want this done, but no so fast! There are hundreds of finished parts in an engine, and redoing all of them costs thousands of dollars. Cosmetic restoration can easily double the cost of a mechanical engine overhaul.
Another thing we consider are updates. For example, older V8 engines did not have good rear oil seals. They always dripped, even when new. We often machine the engines to take the new step rubber oil seals, as shown here:
Updates like this improve the functionality of older motors while being invisible from outside.
Next we look at the ancillary pieces. An engine overhaul may be limited to the internal parts that failed, but when the motor is apart we suggest going through all the external pieces. For example, we might rebuild the alternator, AC compressor, or hydraulic pumps and accumulators while they are off the car and accessible. It adds cost now but saves even more in the long run.
Finally the engine is assembled and made ready to install:
In some models the engine goes in by itself. In most newer cars the engine is mated to the transmission, and both are installed in the subframe, which is inserted and removed from below:
In those cases we often go through the subframe and transmission as well, as they are out for what may be the first time in the car's life.
The results of a well-done job can be stunning:
As you might imagine, this is pretty specialized work. Jobs like the one in these photos can take hundreds of man-hours and a year or more of time. Lesser jobs can be done faster, but you get what you pay for, and as these cars age, the standard of work we are asked for rises each year.
I've used photos from two engine jobs to illustrate this article. The green car in the photos is a 1972 Long Wheelbase Shadow owned by John Rando. That engine achieved the highest score in judging at the Rolls-Royce Owner's Club National meet in Asheville, North Carolina in 2016, and it's headed for Senior Judging at French Lick in 2017. It is an example of the very best that can be done with engine bay restoration on these newer, more complex cars.
John Elder Robison