Early XK120 Steel Car Anomalies

[Christopher_Potempa]

All –

Back in February – just before the covid thing blew up – I bought this second driver car so I could experience the XK120-thing now rather than waiting years down the road due to incremental progress on my other '120 OTS. This is car 670236. Beverly Hills Car Club purchase. From about March/ April 1950:

As I do some light maintenance on this neglected driver, I’ve noticed some anomalies that don’t jive with my later car (670898 from October/ November of 1950), the parts book and my old copy of XK120 Explored. Thought I’d share a few finds with comments invited.

First, the rear door shut panels are all secured to the body with countersunk screws – not spot-welded threaded studs on the back side like other steel cars. Was this something that carried over for a little while from alloy-cars?

Second, the stud-less cylinder head appears to not have any numbers stamped where the engine number repeats itself. I think I once read that early cars didn’t have their heads stamped with the engine number. Is this true?

Third, the wind screen frames have a peg on their top corners instead of a threaded hole where the frames meet that center post top cap. I’m not seeing any reference to this either in my books but it sure looks factory to me.

Here’s a window frame from my late '50 OTS showing the difference:

Securing the frames to the top cap with countersunk screws was a better idea as, in my case, the bottom frame rubber had degraded so much one of the windscreen halves had settled slightly where it meets the center post. Wouldn’t have happened were it secured with the countersunk screws or a fresh rubber seal (something I’m doing now). Nice to know Jaguar was thinking of us 70+ years on with the countersunk screws.

Fourth, the radiator grills really do have ribbed sections:

Fifth, the steering rod on this early steel car does not take any of the replacement pin assemblies commonly sold for these cars. I’d have to do some serious reaming in order to get them to fit. The original pins pictured lying on their sides simply had rubber on them – no outer metal sleeve. No matter, I’ll just turn replacements of acetal/ delrin in lieu of the original rubber and press fit them in in lieu of reaming the holes to take modern replacements. Notice one of the pins (from the driver’s side – LHD) has its washer noticeably larger than the one from the passenger side.

Sixth, the windscreen wiper. It appears to be date-stamped March 1950 (3 50) but has a mounting that I haven’t seen on my other car or in books. This one has/had 2BA studs with flats on top threaded into the wiper body. On top of the flats were round rubbers glued to these flats and then duplicate flats/ studs that in turn screw to bracket on the car. Not sure how I’ll go about fixing this yet.

Finally, I’m kicking myself for not saving the old fuel tank. Wish I’d taken a picture as it’s since been trashed. Does anyone have a picture of what the ones on the alloy cars look like? I have a feeling mine was a carryover from those cars as it was much more angular (best way to describe it) and had the recessed sending unit section soldered – as opposed to stamped in. Regardless, it was pretty beat on the underside and leaked as well.

[Christopher_Potempa]

I’ll add also that it’s this car that has the manufacturer’s tag affixed to the top of the reservoir as alluded to in another thread:

[Rob_Reilly]

I can speak to one or two of these items.
The early track rods, also used on Mark V saloon, went through some development stages.
Here is my experience from 2008.

[xk] XK120 Track Rod Ends

I am repairing the track rod ends on my Mark V, which are the same as most XK120s. These are the later type C4135 and C4136 with rubber inside. I have posted a picture. http://www.jag-lovers.org/v.htm?1222830334 The original did not have an outer sleeve and was not intended to be repaired. The diameter of the hole is .907" and the repair part with the outer sleeve is 1.003" diameter. It did not come with any instructions, but it seems like a straightforward machining job to bore and ream …

Note I did not ream out the track rod end forgings, I filed down the replacement parts to fit.

Your wiper motor mounting is the same as my Apr '50 Mark V and Nov '51 XK120.
I made new rubber discs and glued them on with JB Weld.

The fuel tank construction sounds like my '38 SS, about 25 pieces all soldered together, including the sender unit well. This was a new design for '38 that was not very well planned for high production. They were having all sorts of other problems with body parts at the time, and must have left the fuel tank design until last. What they saved on tooling costs they spent on labor.

Contrast the Mark V, planned for high production, and tooling prepared to stamp them out cheap and fast.

[Roger_Payne]

@Christopher_Potempa

Second, the stud-less cylinder head appears to not have any numbers stamped where the engine number repeats itself. I think I once read that early cars didn’t have their heads stamped with the engine number. Is this true?

Chris, You are referring to my research efforts into early XK heads - but yes, the very earliest XK120 heads did not have any ENGINE NUMBER stamping, with the ENGINE NUMBER still stamped on the BLOCK and also on the cars original CHASSIS/ID Plate. Can you advise this cars original Engine Number as per block and ID Plate and indeed JDHT certificate if you have it.
There are other ways that a Head can be identified without having a stamped in ENGINE No., noting that brand new spare-part replacement heads did not have any engine number stamped on them either.
But as a starting point, this head will have a stamped in Head Sequence Number, most likely found stamped into the flat area forward of Spark Plug number 3, and rear of the Round Plug. Can you take a photo of that HSN or at least advise what number it is. If it is not just forward of Plug No.3 it will be at the flat area at the very rear of the head… See example below of HSN A192 stamping…

[Christopher_Potempa]

Roger, the data plate shows W1495-8. This matches the number on the block next to the oil filter assembly. A JDHT certificate I still don’t have at present as it doesn’t feel important to me right now. But I will get one at some point down the road. My other has one but they don’t seem to really tell you much other than confirming numbers, colors, dispatch date and US distributor.

The cylinder head shows A595 with a faint oval and two circles above and below that number. The oval seems to have JAG 29 inside it. I can’t tell what the others have inside their circles at present.

[Christopher_Potempa]

Rob, construction-wise, my former tank was very much like the one from your '38. As it didn’t match pictures shown in my copy of XK120 Explored, didn’t fit the chassis like later ones, had more of a home-made look to it and was pretty beat, again, I ended up trashing it. The car formerly resided in a Sheboygan, Wisconsin dentist’s garage since '74 so I assumed that it was something fabricated locally in that part of the country anyway. Mea culpa. Feel free to shoot daggers my way guys. Sorry.

Thank you for the track rod link. This is most helpful. Also for the tip about JB Weld with the wiper rubbers. I’ll try that. All three originals were found at the bottom of the bracket and amazingly, they’re still soft and pliable – it seems to have been only the adhesive that failed.

[Roger_Payne]

@Christopher_Potempa

The cylinder head shows A595 with a faint oval and two circles above and below that number. The oval seems to have JAG 29 inside it. I can’t tell what the others have inside their circles at present.

Christopher,
I cannot be absolute, as your A595 is on the cusp of no ENGINE NO. stamping and now having the ENGINE No. stamping on the head, but that in itself pretty well confirms that this is 99.9% definitely the original head for your engine allocated number W1495-8 as per Block and matching numbers ID Plate. Head castings were machined up/assembled then allocated their HSN - in your case A596 but were not then allocated Engine Numbers in numerical order but more usually within a batch, and only then received its ENGINE No stamping after it was allocated. The chances of this being a spare un-numbered head fitted some time later is pretty well ZERO probability, given its A595 is within the cusp of the expected range, and all other head characteristics visible matching OK…

So as far as I am concerned; the HEAD is definitely the original for XK120 Engine Number W1495-8 and is indeed one of the very earliest survivors…

[Christopher_Potempa]

Thank you Roger, that’s helpful to know. Along those lines I suppose I may expect to also find the older style chain tensioner, 5/16" lift cams, a flywheel secured with 6 bolts instead of 10 and a crankshaft fitted with Welch plugs instead of threaded pipe plugs. That last one would be problematic as I was hoping to drop the pan someday, unscrew the plugs and clean the crankshaft oil passages with a brush and solvent to remove any sludge. Welch plugs would nix that idea for me.

[Roger_Payne]

Christopher,
If you want excellent information, excellent photographs, and 99.999% originality accuracy regarding all this early XK120 detail, including internal engine detail, then if you don’t already have it, you must get a copy of Urs Schmid’s JAGUAR XK120 The Anatomy of a Cult Object Volume 1 and Volume 2…
There is nothing at all that comes close to the comprehensive and accurate detail in these two Volumes. Second best, but a distant second is Philip Porters ORIGINAL JAGUAR XK, but it must be the fully revised THIRD EDITION. This book is reliably accurate in what it covers, but covering all XK120, XK140 and XK150 all in one volume, its XK120 coverage is far less than Urs Schmids two volumes on just XK120. There is no third best, although other books have some value, but either have limited or specifically focused coverage (such as Concours Guides), or are simply not reliably accurate… but then that’s my opinion, and I have either co-authored or been a major contributor to both mentioned best and second best, and indeed others that I don’t rate as third best or less, re matters reliable accurate originality…

Sop refer to Urs books for all your crankshaft, flywheel, timing gear etc. issues of your very very early steel bodied XK120 - or any other XK120

[Christopher_Potempa]

You’re doing a pretty good job of whetting my appetite for these books, Roger. What is it about these cars beyond their good looks that make the most arcane details so endlessly fascinating?? Okay, I’ll give some serious thought to adding this to my personal Christmas wish list.

I have Porter’s book as well but since it’s from 1988, I’ll assume it’s not the coveted third edition.

[Roger_Payne]

@Christopher_Potempa

I have Porter’s book as well but since it’s from 1988, I’ll assume it’s not the coveted third edition.

Nope. The recommended book is the Revised 3rd Edition as clearly shown on the lower-right corner of the dust-jacket, but not on the book itself. Inside first page it clearly shows First Published in June 2012. This 3rd (2012) Edition is totally different in all respects, and is vastly improved over the earlier editions (and printings) that share only the same title Original Jaguar XK by Philip Porter.

Also worth getting is the Jaguar Daimler Heritage Trust publication Jaguar XK120 in Detail, by A.D. Clausager (when Chief Archivist) published in 2006. This book is the ‘bible’ on original factory sourced statistical information including production changes, colours and colour schemes, but does not purport to be an originality/authenticity guide, but a lot of really good - and accurate - data, that all other XK120 books borrow from heavily. Its accurate! .

[Terry_McGrath]

There is always of course XK120 explored with the latest revised edition and there are some special prices for xmas

Paul Skilleter Books - Excellence in Automotive Publishing: Buy Jaguar XK 120 Explored THE PLATES Bernard Viart (In English)

[peterjb (peter balls)]

@Christopher_Potempa

. What is it about these

Three iconic two seaters Christopher, where the >
SS100 evokes “era”, the Etype exudes “extrovert personality,”
but the XK has “soul”, perhaps because, gestation, birth and identity are / were
decided by its heart.

[Rob_Reilly]

@Christopher_Potempa

What is it about these cars beyond their good looks that make the most arcane details so endlessly fascinating??

For me, it was seeing one parked in a driveway, every day riding the school bus to high school. It had three racing stripes on the side with the letters XK120, like a GT40.
Twelve years later I got one, and the obsession with returning it to original began with correcting all the bad repairs done by previous owners. From the books about British cars written by British authors I learned the British slang term “bodge” meaning a sloppy repair. I also bought two or three parts I discovered to be incorrect, at a time in my life when wasted expenditures were a not insignificant factor in my finances.
Thus formed in my psyche the need for accurate information.
When I got on the internet on a newsgroup called rec.autos.antique and found two or three other XK120 owners, they also had questions about “Why is my car different from other XK120s?”; and thus the eternal quest began…the never-ending story.

[Sroope (Simon Roope)]

Roger,
Cylinder head no A653 has the engine number, W1431-8, stamped at the front of the plug valley.

[Christopher_Potempa]

That’s interesting. Thanks for contributing this. I’m now curious to know what other cars from around this sequence of engine and head casting numbers have or don’t have on theirs?

[Roger_Payne]

Thanks Simon - another positive sighting/photos to add to my growing evidence data base of these FIRST TYPE Heads.
This now pictured Head with HSN A635 is also one of the very first XK six-cylinder Heads - Jaguar Part Number C.2242 of which only 138 actually ended up fitted new to an XK120 allocated its Engine Number in range W1001 to W1880 and then in batches to a highest W2483, intermingled with the next variant C.2242/1 Head. The fact that the HSN shows A635, being the 635th head indicates that these HSN were shared with 4 cylinder XK and XJ and other experimental heads, and indeed a certain amount of wastage of Heads that were rejected by one of the several quality control checks performed during the machining up/assembly of the raw head casting. That indeed is what the JAG29 within an Oval stamping is adjacent to the HSN. This is the stamp of the Jaguar Quality Control inspector #29 who would have been tasked with checking a certain aspect of the machining/assembly and if OK applied his JAG29 stamp as a record/proof, and if not rejected for rework or often back to foundry and melted down to start again.

Bear in mind this all happened well before a completed Head was actually finished, then stored, until drawn from stock after being allocated to a specific complete Engine Build/assembly with an allocated ENGINE No to be stamped in, initially the ENGINE NUMBER being stamped on just the block, but after a short while also on the Head.

Note all these first variant Heads have what is called the Siamese-Spark Plug recesses, and if Simon has an underside photo it will have cast in lettering/numbers that identify these as being cast up by the WILLIAM MILLS foundry as indicated by the WM351 cast number…

There are lots of other clues as to the identity and status of all XK cylinder heads, apart from the most obvious Engine Number stamping - that can be and has been faked for a variety of reasons, but thus my earlier comment that Christophers Head (his XK Head that is ) is in my opinion, 99.9% definitely the original for his very early 670236 - nothing is ever 100%

AS you would expect this 1949/50 period was most interesting in a Production Engineering sense, and indeed I find more interesting and more of a challenge that when things soon got more boringly straight forward…, until things got interesting again with the development, prototypes then production of the C-type head in late 1951 on…

[Rob_Reilly]

This sort of research is very interesting to a few of us.
So this cylinder head numbering may have begun approximately about May-June '50.

Has anyone ever heard a reason as to why they began numbering XK cylinder heads? It’s not a matched set with the block, in the same sense as the front timing cover and main bearing caps.

The pushrod heads are not numbered, so this subject of head IDs never comes up on the pre-xk forum.

[Rob_Reilly]

@Roger_Payne

only 138

I think it was 1345 engines had this first head with the half seals at the rear of the camshafts. They must have been leaky, because that’s one of the first things they changed.

[Roger_Payne]

@Rob_Reilly

Has anyone ever heard a reason as to why they began numbering XK cylinder heads?

I am not aware of any definitive/official reason, but suspect it may have been feedback from Dealerships where there local Registration authority registered new cars based on Engine Number identification, with some actually adding in the number themselves to satisfy the local authorities…

See attached example on a very early aluminium XK120, with HSN A105 - the stamped in ENGINE NUMBER was done in Australia, and not by the factory…

All part of the reason I don’t believe there will be an exact demarcation of when Jaguar started stamping in Engine Numbers on head, maybe staggered for certain markets first, before being standardised across the board. I just don’t have sufficient reliable data/evidence to be any more conclusive, apart from its inconsistent over about A500 to A600 HSN for UK and USA cars, but we have examples in Australia of factory stamped Engine Numbers in the late A100s and A200s - so maybe a ‘special’ for Australia
And its not impossible that the pictured A105/ W1058-7 may well have been the factory stamping prototype, its just I have always attributed it to a local NSW Registration requirement when car was new/first registered - impossible to know for sure now…