Thursday, May 7, 2015

Interpreting body and engine serial numbers of Bentley & Rolls-Royce T / Shadow era cars

One of the things car collectors often ask is - Does the car have matching numbers?  In this essay I'll show you how to check the engine numbers on the Bentley T / Rolls-Royce Shadow series, and how they compare to the chassis numbers shown on the body, the registration, and the certificate of title.

The photo below shows a rebuilt and detailed engine for a Silver Shadow.  The Bentley version looks exactly the same, with different logo on the valve covers.  A Cloud or S series V8 would look similar.  The later engines (Spur and onward) look a bit more finished, and they have more complex trimmings but they are otherwise the same.  As you can see, the finish of the aluminum engine block casting is surprisingly rough. That really shows what a cottage industry low volume car building was in England 50 years ago.

Mercedes or Ford blocks of this vintage are much more precisely and cleanly cast.  Crewe engine designer Jack Phillips says the engine looks this way because it's cast from LM8 silicon aluminum alloy, which is very difficult to machine.  That may be the explanation, or it may be part of what "hand built" means, as opposed to coming off a high volume production line . .



I'll show you how to find the identifying numbers on the engine, and how to match them to the body.  But first, a short explanation of what the body numbers mean . . .

Silver Shadow/Bentley T cars are registered by the chassis number which is visible on the tag atop the dash, visible through the windshield frame, and on the data plate under the hood.  The number is decoded as follows:

For cars build from 1965-1980, the first character denotes body style:
S = 4-door saloon 
C = 2-door coupe
D = Drophead, or convertible
L = Long Wheelbase 4-door

J = Camargue

The second letter is an R for Rolls-Royce or a B for Bentley

The third letter denotes the car's original market and in some cases year:
H = Right-hand drive, RHD, Home-market (UK)
X = Left-hand drive, LHD, Export, including North America prior to 1972
A = North-American model, 1972
B = North-American model, 1973
C = North-American model, 1974
D = North-American model, 1975
E = North-American model, 1976
F = North-American model, 1977
G = North-American model, 1978
K = North-American model, 1979

L = North-American model, 1980

The digits that follow are the sequential production number, but recognize that the factory skipped numbers and jumped the numbering to the next 10,000 when there was a major design revision.

The photos below are from an old Rolls-Royce manual, and the show the locations of body serial numbers:






There are two engine numbers on most RR/B cars.  One is derived from the chassis number, the other is the engine's sequential production number.  Engine and body assembly proceeded in parallel, and started and stopped at different times, so these numbers are not aligned by any consistent formula. 

Crewe refers to the chassis-related number as the engine number in their contemporaneous service literature:


In the photo below you see me pointing to that number stamped on the left front corner of the block of an actual engine.  This location is hidden beneath the alternator and AC compressor on an assembled car, so some disassembly is usually required to reveal it.  It's easy to see when the motor is on a stand, as in this photo.


Here is a closeup of the number


These are the significant points to what you see here:

  • The number 14159 matches the body number of the car this motor came out of; in this case a long wheelbase 1972 Shadow;
  • The hand stamp character of the number is representative of RR practice of the era;
  • The stamped surface is level with the block deck at the edge of the head (top of photo) so we know the stamping is original, and not ground down and re-stamped.
  • You can see the file marks where the block was filed and smoothed as a rough casting, and you can see the finish marks where the deck surface was ground (in the stamped area.)  This is further evidence of originality;
  • Rolls-Royce did not stamp body numbers into the blocks until they were assigned to a vehicle. That happened when a motor was assigned to a body in the factory, and it sometimes happened again if a motor failed in the field and had to be replaced.

Consequently, while we know this is an engine that was supplied new by Rolls-Royce for the 14159 car, we do not know this is the ORIGINAL engine.  It could be a factory replacement installed under warranty.  Further evidence of original fit (or not) comes from other marks:


In the photo above I am pointing to the engine's sequential production number, which is hidden beneath the intake manifold, itself hidden under the AC compressor and other bits atop the motor.  This number was stamped when the motor was assembled, and identifies the motor's place on the RR/B engine assembly line.

Silver Cloud V8 motors have their sequential number stamped in this same location but at the rear of the motor, next to the distributor.  Cloud motors can also be distinguished from Shadow engines by their lack of hydraulic pumps atop the valley cover, and the location of spark plugs beneath the exhaust manifolds.

Below is a closeup of the production sequence stamping, and an overall shot of the top of the block in that area showing the engine number on the left, the part number of the block in front, and an un-used number stamping area on the right.  Note the difference between this stamping and the body number, which was stamped when the engine was assigned and placed into the 14159 car during final assembly.

These photos were taken on a rebuilt engine before the intake manifold was fitted.  You can use a fiber optic camera to see this number on an assembled engine.  The hole in the top center is for the front hydraulic pump, and the front intake ports are visible on the heads at top left and right.



The letters SY denote a Silver Shadow or Bentley T series engine.  If these are the only letters the engine is a 6,230cc unit, made between 1965-1970. The addition of the L denotes a long stroke 6,750cc V8.  The factory changed to the larger displacement engine from chassis number 8742 in the 1970 model year. This is the 5,368th long stroke Shadow series V8 produced.

Looking at the two stamped numbers, you can see that the typeface is the same, but the hand stamping them is different; they were clearly done by two people.  If this number matches the engine number on the car's build sheet, you know you have an original motor.  If this number is different, then you have two possibilities

  • The factory build record is wrong (a very real possibility), or
  • If the body number matches the body, but this number does not match the build sheet then the motor you are looking at is a factory replacement engine

If both numbers are different the motor was almost certainly transplanted from another car.

Note the relief of the face the number is stamped into, and the bubbles (holes) in the aluminum casting in this area.  This is typical of the low volume, low pressure casting process they used at the time.  If bubbles like those were to appear near a water jacket the metal of the block would be porous.  This photo gives you an idea how that happens.

There was a time that Rolls-Royce supplied rebuilt engines and blocks.  In those cases you could expect to see the original numbering surface milled away and a new number with a "rebuilt" symbol stamped in the freshly cut area. The appearance of such a rebuilt stamp would be recognizably different from the first-time stampings shown in these photos.

This next photo shows the part number of the block, and was cast in when the block was made. To the right of the part number, at a 90 degree angle, you see more numbers which we think are the production month and year (6 72)  Adjacent to that, in a slightly more worn typeface, is another number, 70.  We think the 70 is the year of the last revision to the engine block casting mold, and the 6 72 is the date of this particular casting. However, we are not certain of this.  It was not unusual for Rolls-Royce to buy major components (bodies, engine blocks) in quantities that would last them several years.

The part number is cast into the top front of every Rolls-Royce engine block
Engine block showing the 70 and 6 72 date marks
Shadow engine blocks were grey aluminum color. The heads and intake manifolds were black.  The exhaust manifolds and many of the brackets were bare metal. Other series of RR/B were finished in different patterns. For example, Phantom engines of the same vintage were all black.  Therefore finish on the engine may be a further clue to its provenance.

Looking at this top view, you can see that the numbers I've shown you are buried pretty deep, but they are in there on every Shadow, if you want to find them . . .


But like I said, the numbers are hard to find. The photo below shows a Shadow engine bay, and gives a sense of how deep-down the engine block markings are.  Budget a day of labor to check all the numbers on one of these cars.


There are many other parts that you can check for originality.  Quite a few of the important bits were dated or signed as they were fitted.  For example, the brake accumulators are engraved with part numbers and the assembly date, in the summer of 1972.  That's consistent with the production data we have for the car, which was described in this article a few years ago.  You may not be able to see this if the accumulators are dirty but polishing will reveal it.


The part numbers on these accumulator were hand-scribed, as were the assembly dates of August 17, 1972. That date is a few days before the factory delivered the car to the Port for shipment to America.



There are some other markings we have yet to figure out. For example, there is a boss on the right side of the block stamped PB17. What does that mean?  I don't know.  Maybe someone will chime in.


This is a closeup of an un-used number stamping area on the front of the block, to the right of where the engine number is stamped.  As an aside, newer RR/B cars have their engine numbers stamped in this space.  In this car, the space looks empty but close examination reveals a 1/4 inch circular stamp - I suspect it's a QC inspector's mark. It says RRMC 7F.


There are no serial number marks inside the engine, but the main bearing caps are stamped with the same type face used for the serial numbers, to denote their proper position front-to rear.


The cylinder heads have the vehicle number engraved in them, if you care to remove them and look . . .


What about the transmission? For many years, Rolls-Royce bought transmissions from General Motors.  Here is a GM400 from a Silver Shadow:


There are a few distinctive marks on this gearbox.  First of all, there is a large RR ink stamp on the top right of the bell housing:


That mark was probably applied at GM, because the Rolls-Royce gearboxes had different valves from the regular GM units.  There is also a metal tag on the side, which on this car is stamped 72-RR  2958. 72-RR seems to be the year and Rolls-Royce.  2958 is the unit serial number which appears to reset periodically, perhaps at the start of model years.  So this would be the 2,958th gearbox fitted by RR for that model year.  Interestingly, the Silver Shadow historians claim 2,473 cars were built in the 1972 model year.  It's possible there was "model year overlap" in gearbox usage, and there were also transmissions used in Corniche, Phantom, and other models.  We know this car was at the end of the 1972 run.

Here is a description of the transmission number plate from an old workshop manual:


The engine and transmission are carried on the suspension subframe, and the subframe is stamped with the body number next to the steering box, as shown in the photos below. There is a QC stamp in the same location on the opposite side of the subframe.  If you find a car where these numbers are different it was either stolen or repaired with a subframe from another car.




The photo below shows the Silver Shadow body, engine, and subframe separated, prior to reassembly.


Each of these major parts is numbered for identification, and in this case they all match.  Do yours?  I have no idea how many Rolls-Royce motorcars have mismatched numbers, either from mechanical repair, accident repair, or concealment of theft.

There are also numbers on body and trim - for example, on the back sides of the wood interior veneers and on the rear faces of the leather trim. The photo below shows several pieces of wood trim from 6368, a Spur-era car.


I have found the wood numbering to be inconsistent.  This piece - from the side vanity mirror of a LWB Shadow - is not serial numbered, but marked LWB with a sequence number that can sometimes (on coach built cars) be correlated to the car's final serial number.



John Elder Robison is the general manager of J E Robison Service Company, celebrating 30 years of independent Rolls-Royce and Bentley restoration and repair specialists in Springfield, Massachusetts.  John is a longtime technical consultant to the RROC and other car clubs, and he’s owned and restored many fine vehicles.  Find him online at www.robisonservice.com or in the real world at 413-785-1665

Reading this article will make you smarter, especially when it comes to car stuff.  So it's good for you.  But don't take that too far - printing and eating it will probably make you sick.

2 comments:

Greg Prosmushkin said...
This comment has been removed by the author.
Greg Prosmushkin said...

Very informative! One of the best feelings in the world is when you restore a classic car back to its former glory
Greg