XK 120 Lever Pivot for adjusting seats: early versus later

Bob,

Weren’t the pivot screws chrome? Looking at XK120 Anatomy vol 2 p. 70, 73 the nuts were cad plated, so the assembly was not painted as a whole.
On page 70 photo 3 it looks as the nut is chrome as well.

PN is BD3255 and has not changed.

Tadek

Tadek,

I understand that the “early” versions had a chromed pivot screw, but later ones had the pivot screw painted in the same colour as the seat frame.
You’ll find that remark in Viart’s book. Nothing on the subject in Urs Schmid book nor Porter’s.

Nothing known about the introduction date but it wouldn’t surprise me that it coincided with the date the seat frames were no longer chromed. The Pivot Screws would then be painted as well. Of course there might have been a period during which old stocks would have been cleared.

Terry McG confirmed a change-over to grey but also mentions that the chromed screws were slightly different in having a more pronounced head than the later painted versions.

Rob R. showed a picture of 679840 from July 1952 with painted seat frame and pivot screw. .My own April 1954 (although rather late as a change-over date ) had the screws painted grey/green. The XK 140 had painted pivot screws from production start.

Your (late 1953) XK 120 should have had the same painted screws as mine. Note, however, that almost all replacement screws BD.3255 offered today, are chromed (and probably also the case for those offered many years ago so yours might have other pivot screws).

Bob K.

The finish of my screws when I got the car was … rust. :slight_smile:

I faintly remember I noticed trace of chrome, so I chromed them, but I could remember wrong.

However, the nuts were definitly chromed.

I am attaching some relevant phots:


DSCF7338


Also notice the finish of the washer on the pivot pin and its washer.

Tadek

My seat frames were never rusted, but the paint was worn. The frames got new paint 15 years ago. As Takek contends, the nuts for the pivot screws and the washers on the pivot screws were chrome plated. The chrome plating was not to a modern “show chrome” standard - just a protective coating.

679187 Nov '51 has the original painted seat frames and chrome pivot screws.
The nuts are not chromed.

So quite some differences over the years.

The Pivot Screw BD.3255 was used from the start of production with the Alloy XK 120s until the end of the XK 140 production. Initially chromed but later (starting when?) painted. The XK 150 used a different Pivot Screw, BD.11073 with 3/8" UNF thread.(against 5/16" UNF for the earlier Pivot Screw).

The Washers between the Pivot Screw and the Hinges of the Seat Back were BD.541/10 which is a flat “special” washer but I cannot find any reference to the word “chromed”. May be somebody else has more input. Some years later the XK 150 used flat Brass washers BD.541/7 with a 3/8" ID.

The nuts are C.2441/2, identical to the nuts used on the Intake Manifold. Roger P. describes these nuts “a standard 5/16” UNF machine-nut… which was CHROMIUM PLATED", As it was used in large numbers for the manifolds, it probably has been used for a longer period for the Pivot Screw (although these nuts are largely covered by the seat cushions, so there was no absolute need to have it chromium plated). These nuts were continued on the XK 140. The XK 150 went back to a standard nut UFN.237/L. no longer chromium plated.

Bob K.

A clue to that mystery washer is that it is given a BD reference. My understanding is that Standard Parts as listed in the rear of the SPCs are generic hardware whereas anything BD has been modified in some way. So if not chromed perhaps BD.541/10 has just been resized to accommodate the pivot if not manufactured in house for the purpose.

The only thing I can say about what remains of 660752 is one chromed pivot in a chromed frame with a nut as listed above (edited) … and the washer in question has no evidence of chrome on it but whether through wear or design is split on one side (perhaps a spring washer), so rather than a round washer it is now a tight C washer.

Jason,

As far as I know, BD stands for parts related to the Body. This was a very early coding system for these parts, introduced in the Thirties by SS (Jaguar).
Might well be that the part is special regarding dimension or surface treatment.

Bob K.

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where people are noting chrome nuts these are not actually chrome plated they I believe are nickell plated same as the nuts that hold the inlet manifold on.
On rob reilly’s seats chrome pivot bolts unusual as usually these are painted when seat frames are painted. There are also two different profiles of these pivot bolts.

No trivia too insignificant for this group!
Chrome shoulder bolt
big washers clean but I won’t claim any plating
lock washer no
nut no
20230316_120955
I would think the separate frame parts were painted before upholstering, and then the back attached to the base frame afterwards.
Thus the bolt heads would not be painted.

Jason,
SS cars Ltd (not yet Jaguar) took advantage of the WW2 close down period, to develop a totally new Part Numbering and Engineering Drawing system for the resumption of post-war production of the now suspended manufacture of the 1940MY SS Jaguar Saloon and Coupe. The new system was predominantly set up in two streams - the C.xxx prefix Chassis related stream, and the BD.xxx prefix BoDy related stream, albeit a part introduced first as a C.xxx prefix number, if used later on the body still retained its C prefix part number - and vice versa… There was also ongoing residual use of all-numeric SS part numbers as used during the 1936-40 SS Jaguar period.
The earliest date I have is for part number C.28 (so close to the first), with the associated Engineering Drawing on SS Cars Ltd letterhead is dated December 1938, but this is very much years ahead of the main work done, which was mostly in the 1942-44 period which is of prime relevance…
During WW2 the British Ministry of Supply controlled all British Industry manufacture, and supply clearly prioritized for the War effort, and one of the things they did was set up an outline for a standard form of decodeable-identification for ‘standard’ fasteners - and by ‘standard’ I mean one that complied with the relevant British Standards. SS Cars/Jaguar of course had to adopt that requirement in their new developing Part Numbering system. Thus in any post-war car, all ‘standard’ fasteners had ‘decodeable’ part numbers (Jaguars interpretation of the Ministry of Supplies guidelines), and all ‘non-standard’ fasteners were simply incorporated within Jaguars new C.xxx and BD.xxxx prefix part numbering system…

So where a Jaguar Spare Parts Catalogue advises a washer (for instance) to be a Part No. BD.541/10 you know immediately that it is ‘non-standard’, but unfortunately you don’t know exactly why it is non-standard without access the Jaguar Drawing for a BD.541/10 - or have built up your own/or shared data base, based on physical examination/identification/recording of each specific non-standard Part Number. From my own data base (in progress) I can tell you that BD.541 is an allocated group of non-standard size, but otherwise standard flat washers. I have identified this family includes 14 members, numbered BD.541/1 to BD.541/14. All are flat plain washers, most steel but some brass, and of variable thickness, inside diameter and outside diameter, with no apparent sequence/order of size (as you do get in other ‘families’). I have identified/recorded the exact sizes of 10 only of these fourteen and as per Murphie’s Law, BD.541/10 is one of the four that I have yet to measure/record, but that’s my laziness only. I know BD.541/10 is used on XK140 seat frame pivot bolts, but despite having my original/unrestored seat frames under my house in storage (not yet ready for them), I have not yet measured them, nor indeed checked whether brass or steel, and I suspect maybe brass… But if anyone else is not so lazy, I would appreciate getting material/dimensions advice to add to my data base, and while you are at it, also BD.541/4, /6, /11 and /12 (yes, I know that’s FIVE missing not four, but I have the dimensions of one of these, but don’t know its suffix number)

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UFN.237/L is actually a LOCK NUT (as denoted by the first number ‘2’), not a STANDARD HEX NUT (which would have a first number ‘1’), but by XK150 the decodable detail is also slightly updated…
UFN = Unified Fine thread Nut, whereas originally a NN prefix would have been used (National Fine Nut or ANF), with the /L suffix still denoting STEEL, but a steel grade one step weaker than the D (later R) grade of the compatable bolt/setscrew. The logic was a weaker nut would strip before the stronger bolt, if overtightened, albeit that doesnt always seem to be the case :slight_smile:

But why a Lock Nut - these were usually used in pairs, but in this case no - four BD.11073 pivot screws, and only four UFN.237/L Nuts. But in conjunction with a Shakeproof washer, and a brass flat washer, suggests to be a clearance issue, and probably a shouldered Pivot Screw. Need to physical see/view…

Well that’s funny. I put the bolt and washers back on the car, and now you want measurements. :upside_down_face:

Ok here’s BD.541/10
ID 0.530"
OD 1.132"
Thickness 0.048"

Looking at it in strong light, maybe there is plating but not much of it.
It’s late and I’m sleepy. :yawning_face:
I’ll look at the other 7 tomorrow.

Roger,

You’re correct: this is the shouldered XK 150 Pivot Screw BD.11073 , clearly different from the earlier Pivot Screw, having a hex head now.

Agree (more or less) with the measurements of Washer BD.541/10 by Rob R.
ID 1-17/32"
OD 1-1/8 "
Thickness 3/64"

I brushed my Washers and the surface is presently grey/black . I cannot say what they were when new.

Bob K.

I examined four of the big washers. The thickness varies from 0.048" to 0.050" but I did not find any conclusive evidence of plating. There is rusting around the edges but not in the centers, and in fact the centers are worn smooth due to the friction when moving the seat backs as I frequently do to access the storage compartment of my FHC. I also assume the rusting around the edges is from natural atmospheric moisture, which is probably less in a FHC that has had indoor storage for many decades than what it would be in an OTS or a DHC which had lost it’s top.
In any case, the washers are not really very visible, mostly hidden by the big head on the shoulder bolts, so I am less inclined to believe they would be plated. I am more inclined to believe the BD part number was assigned because the dimensions are unusual, not being a standard flat washer.

I don’t know if the parts numbers will clearly tell whether the pivot washers were chrome plated, but here’s a possibility. Your car was built two years before mine during the “nickel shortage.” Maybe that’s why the washers and nuts on your seat pivots lack plating. I few years ago, I had sets of chrome-plated intake manifold nuts made for the XK forum, and I recall you ordered a set for your FHC.

When I worked on my seat frames about 15 years ago, I concluded the washers and nuts were originally chrome plated - but not to a high quality standard. The washers extend beyond the pivot heads, and I felt they looked unsightly with what was left of the weak chrome plating. I ended up purchasing new chrome plated washers for the two that show when the doors are opened. These are better chromed than the originals. Maybe a bit over the top, but this was done years ago based on my forensic analysis at that time. If I were to do the job today, I would probably send two of the originals off to my chrome plater for a less pronounced chrome shine.

Mike,

May we conclude from your contribution that the Pivot Screw itself of your 1953 XK 120 was factory painted and not chrome plated?

Bob K.

Yes, that’s correct. The pivot screw heads on my November 1953 OTS were originally factory painted - not chromed.

Thanks Rob, I will enter dimensions and material for BD.541/10 on my excel spread sheet for ‘non-standard’ fasteners…

I note your exact dimensions, but for my purposes I try to record such things as I believe they would have been done by Jaguar Engineers in the 1950s, and thus how I believe they would have been specified on the Part No drawings… For BD.541/10 I now show it as being…

17/32"Ф - 1-1/8"OD x 18 S.W.G. (.048" thick)

I use the symbol Ф to denote the nominal bolt diameter of this washers application, as it is not critical to a decimal place measurement, so always in imperial fractions, usually only however to 1/16" accuracy, with 1/32" unusual but maybe as part of this Pivot Bolt arrangement design - whatever 17/32" works… Similarly a washer OD is again never decimal place accurate, so again to the nearest 1/16", albeit so far I find 1-1/8in a common OD for non-standard washers (As per Bobs 1-1/8" measurement) - larger than standard, but not as large as a typical body washer…
And thickness - washers were invariably always made in UK from rolled sheet steel, which was always supplied in S.W.G (Standard Wire Gauge - a British standard gauge) thicknesses, which of course was of a thickness that had an acceptable tolerance. But as my memory of SWG thicknesses is not what it used to be, I show the SWG number with its decimal equivalent in brackets, albeit an accurate measurement of the actual washer thickness can be +/- 1 or 2 thou… Thicknesses of washers are never shown in inch fractions (Bobs quoted 3/64" = .0469", so within 18 SWG tolerance), and only rare fully machined precision washers shown in decimal inches. So for those not used to SWG thicknesses, see table below…

24 SWG 0.022"
23 SWG 0.024"
22 SWG 0.028"
21 SWG 0.032"
20 SWG 0.036"
19 SWG 0.040"
18 SWG 0.048"
17 SWG 0.056"
16 SWG 0.064"
15 SWG 0.072"
14 SWG 0.080"
13 SWG 0.092"
12 SWG 0.104"
11 SWG 0.116"
10 SWG 0.128"
9 SWG 0.144"
8 SWG 0.160"
7 SWG 0.176"
6 SWG 0.192"
5 SWG 0.212"
4 SWG 0.232"
3 SWG 0.252"
2 SWG 0.265"
1 SWG 0.300"
0 SWG 0.324"

But also useful - and fairly conclusive - it’s a plain bright-steel washer, not plated, and not Brass as are some other BD.541/x washers…

Roger,

Very clear story and thanks for correcting my typing error!

Bob K.