The first and foremost quandary concerns those circles on the Pc and BcB styles. The general understanding is that the
later markers had their numbers enclosed in a small, 5mm diameter circle.
The earlier markers had a slightly larger number that was not circled.
That's not too hard to comprehend, but the REALLY difficult fact is that there are NO drawings
that indicate any of the markers should have circles on them.
All drawings for post-Ghost markers (except PIII) dimension the characters as 0.150" tall.
The letters 'M' or 'B' on the back side of existing samples are never circled. These letters and the numbers on uncircled
styles all have characters that are always 0.15" tall. But for
those with circled numbers, the numbers are only 0.135" inside a 0.19" circle. Style Pc, which has no back
side letter, has a blank 0.19" circle on the back. A first assumption was that the circles came into being
when the part numbers changed; but no drawings, new or old mention circles.
The LOP's indicate that the earlier part numbers for styles P and BB were used until 1937.
But if an updated, circled style was not used until
1937, that would indicate a very paltry number of the circle style markers were ever used.
In fact, there are probably as many, or more Pc and BcB samples in existence than there are P and BB.
Either a majority of the old style markers were replaced during regular service or the circles must have come
about while the part numbers stayed the same.
So the question becomes: since the circles may have been added long before the part numbers changed, how do we
know which cars should have circles and which should not?
The PIII drawings hint that drawing numbers were changed when a supplier or material changed
and that such a number change did not necessarily indicate that the part appearance was altered.
The PIII sleeve characters are 0.11" tall, front and back, and enclosed in a
0.19" circles similar to that of Pc and BcB. The PIII circles, like the others, are NOT mentioned on the drawings.
There are two sets of sleeve numbers and drawings for PIII; one for the A, B
and C series cars and the other for the D series. The drawings differ only in that the latter calls
for the use of brown Erinoid material. The PIII community consensus is that all series
used markers that were visually identical, the drawing number change
was only indicative of a change in material and/or supplier.
The current assumption is that, since the P was in use on the 20/25 alongside the Ghost Gp style,
that both remained uncircled for all 20/25. We further assume that the change to
circled numbers may have happened in 1933 when a combination of styles P & BB (with circles, that would make them
Pc and BcB) was used for the first time on the 3 1/2L Bentley. But honestly,
there seems to be no printed information to say one would be wrong using a circled number style on a 20/25 or even a Ghost.
It is, shall we say, an 'owner decision'.
If the parts are specified to be black, there isn't a great question as to what that means.
But what color are they when the specification is brown? Brown can be a variety of colors.
This photo is of a single set of original
markers that were cleaned, polished
and photographed in bright sunlight. They are 6 different shades of brown, which
is the correct brown, if any? For all the samples examined, the lightest colors seem to
be a light chocolate brown, the most common is a similar to a Hershey's® Special Dark® chocolate, while the darkest are a
deep dark brown that is almost black. Take your pick as to what color 'brown' might be. Not that we planned
it that way, but upon close examination, our reproductions have a slight variation in color similar to most original sets. And luckily, for those
styles which were originally black, we can alter our process to produce markers that are very near, if not
exactly, black. Without a very strong light source, they can appear black if that is desired.
All of the drawings except for the very last set of Bentley drawings
in 1938 call for an ID of 0.265" +10, i.e. 0.265" to 0.275" was permissible. (The 1938 drawings called
for a 0.281" ID but because of WWII it is unclear if parts were ever manufactured from those drawings.)
At the large end of the range all is well since a rubber covered, 7mm wire (0.276") fits easily into a 0.275" ID bush.
all unaltered samples appear closer to the 0.265" dimension. Even if you lubricate the wire, it is difficult
to get a 0.276" wire into a rigid, 0.265" cylinder. As a result, a large number of original samples show signs
of having the ID filed to allow an easier fit. The skill of those wielding the files
varied from very good to awful. It is not uncommon to find examples with oval or exceedingly large
ID's. In our reproduction process we attempt to select originals with circular ID's close to 0.275" or smaller.
For the smaller IDs we then sometimes must modify the master copies (leaving the originals unaltered) so
that the repros will more properly fit modern wires.
The 20HP parts book calls for styles P, Z and Gp on the earlier cars. The Z apparently was dropped
when the coil connection to the distributor came in through a side plug. For the first 674 cars, there was an option
for an E06 magneto. It is not known how many 20's came with this option. But for those that did, the parts book
indicates the usage of 2 sets of B with 2 sets of M markers (like an aluminum head PI) instead
of 1 set each of P and Gp which were on most 20's. But how can a 20,
which has only a single set of spark plugs use 4 wire markers per cylinder?!?
We are open to suggestions on a resolution to this one but it would appear that the printed quantities
required by the 20 parts book resulted from a human error in copying similar information from a contemporary PI parts manual.