Early 120 cam cover oddity

Has anyone ever seen on an early 120 with the 8 stud cam cover siamese head, an 11 stud cover with the 3 front stud holes never machined or drilled? A 120 came in for rest. that was very un-molested under the bonnet with a pair of these covers. The boss and I both said it was the strangest thing and we’ve never seen this in 40+ years restoring Jags. Tear down will be in a few weeks so i’ll get some photos. No evidence of welding or filling holes - just the cast aluminum. It looked like the gasket was cork and peeked out the side a bit. We joked : “Hey Basil, we ran out of cam covers. Grab a pair of that new style, but don’t machine the front 3 holes. Just let them un-drilled. Those crazy Americans won’t know the difference.”


I would love to see photos. Are they the high boss cam covers?

What do you mean by “high boss”.


For reference, this is an 8 stud cam cover on my '51 XK120.

And this is what is meant by siamese head, conjoined spark plug holes.

A cork gasket would certainly be interesting. I have been wondering what they used back in 1951 for sealing these. They had leakage around the front, which was the reason for going to 11 studs.

Sometimes a hold-down clip was added by repair shops in the valley between the two covers to reduce the leakage.

I once saw an early Mark VII with 8 stud covers and somebody had drilled and tapped it and added 3 small #10-24 UNC screws where you normally see the 3 additional studs on later covers.

When Jaguar added the additional three stud locations at the front of the cam cover, the bosses were about an inch thick. Known as “high boss” cam covers. About 6 months later they reduced the size of the boss by about half. In the photo the cover on the left is the early “high boss” and the one on the right is the later production cam cover. The high boss cam covers were also used on the C-types, with a slight modification.

1 Like

Phil, we’re always interested in seeing pictures of factory oddities, and if you can include the serial number at the front of the head, and the stamped production letter/number combination usually found either in the middle of the valley such as my E5 above, or at the rear, that would help to identify the year and possibly month of production on that head.

A real strange thing that you’ve never seen these types of covers in 40
Years. Every engine with the non stud head, cam covers, the lot that came back to the works in the 70/80s for recon got binned!

The cam covers are the low boss style as you have on the right, but the front 3 are are not drilled and not machined flat like the other 8. I guess no need to - no studs.


An appropriate red-herring for this topic, but if you really want a RARE XK Cam Cover, I would be interested to know if anyone else is aware of these Cam Covers…

Some time ago I acquired several cam-covers that were earmarked for the scrap-metal merchant, given the value of scrap aluminium, and amongst them were this total oddity to me…

Superficially they appear to be just like any other so called ‘studless’ [as in no stud holes around the front) Cam Covers part number C2217 (Inlet) and C2218 (Exhaust) as fitted to the earliest XK120 engines up to W1880 (and extras up to W2486) before being fitted with the second variant ‘studless’ cam-covers C2217/1 and C2218/1 as fitted up to W4690.
These C2217 and C2218 Cam Covers weigh 1.38kg each (+/-) and are clearly marked with their part numbers C2217 and C2218 cast in on the underside surface as shown below…

What alerted me initially to this much rarer pair was their much heavier weight when you picked them up, 1.98kg and 2.20kg for Inlet and Exhaust respectively, visually similar on the top side, but underneath totally void of any cast-in part numbers, albeit functionally same re stud holes, shape and rear seal machining. But the INLET side [C2217] cam cover had a heavy cast boss of the same size and position as on the EXHAUST side camcover, but remained solid, and was not machined out/threaded to accept the Oil Filler Cap. See photo below of the 1.98kg [C2217] alongside the more common 1.38kg C2217

And a close up of the cast-in boss (on the Inlet Cam Cover - not Exhaust, and undrilled/unthreaded)…

I can make a guess what they are; but does anyone have any definitive knowledge …???


Early C type breather mount point ?
I recall a photo showing this.

I think Peter has it. Here is a photo from Auto Sport Review magazine July 1953 issue, but the photo could have been taken earlier.

It appears that for some reason they wanted to or had to eliminate the normal front breather. But most C-Types do not have this.
This would be done by placing a left hand sand core in the mold for a right hand cover. Those sections are made by individual cores.
The other possibility is that someone accidentally placed a left hand core in a right hand mold. When I was an inspector at a foundry I saw defects like this.
I see it has the half circle cut at the rear for the rope seal, only found on the earliest covers and heads.

The front breather was eliminated on the production C-type, but some early engines still had them. (like E 1001-8)
The C-type has the high boss cam covers on the front as previously discussed and seen in Robs photo above. The intake side cam cover was a special sand-cast part and a bit heaver. (I think the standard cam covers were die cast?) It was a special part with a raised boss and the addition of two studs for the breather to attach with Oddie nuts.

On the exhaust cam cover the oil filler opining was specially machined from the underside to receive a threaded collar and red washer that screwed in from the bottom, sealed, and provided threads for the Monza cap


I’ll dig around and get the correct part numbers for each, if anyone is interested.

A further variation on a theme, C8728; exhaust cam cover with threaded Monza oil filler and ‘home made’ looking rear breather. The part number suggests D-Type rather than C-Type.

Limited discussion on the XK forum at Exhaust Cam Cover - C8728 Photos from this thread and a few more attached.

C8728_1 C8728_2 C8728_3

Thats Great Peter, thats all I could think off but with mine still solid and no machined hole, I was struggling to be sure…
The fact my matching-pair are ‘studless’ makes them earlier Cam Covers (given with the XK120 CamCovers the extra studs were added from ‘about’ May 1952 onwards) so predates the 1952 LeMans C-types and of course the 50 “Production” C-types…
So I looked for good photos of the 1951 LeMans C-types - still with their 1951 race Engines, given post 1951 race they got new/later upgraded engines. Best I could find is as below…


Easy to tell this is the 1951 race engine, as still fitted with H6 carburetters and not H8 as introduced for LeMans 1952 engines, and note ‘studless’ cam-covers (as expected for June 1951) but no inlet side additional cam cover breather, but if you look closely the exhaust-side filler cap looks like it incorporates a breather…

Further looking I found pics of the engine fitted into the ‘tool room’ standard REPRODUCTION of XKC003 as reconstructed by Jerry Booen apparently to its May 1952 Mille Miglia specification which judging by photo accurately features correct H6 carburetters, studless cam-covers and same breather arrangement…and if so surely not yet using my inlet cam-cover with unused provision for a separate cam-cover breather …

XKC003 REPRO - Engine

Will see what the later comments say - and I see there are more comments which is great…


The diameter of the uncut hole in your inlet cam cover looks to match the diameter of an round oil filler cap rather than an oval breather. The oil and breather castings are raised on the top side of the cover; is yours raised or flat? If flat, I think Rob’s suggestion it is a defect may be correct.


I seriously doubt it was a mistake - that doesn’t explain the major difference in the mass of these ‘strange’ cam covers (1.98 and 2.20Kg) versus the ‘normal’ C.2217/C.2218 both being only 1.38kg.

Great photos from E1001-8, but my inlet cam-cover does not have the raised platform on the outside/topside of the cam cover - just on the underside, but it is round and same diameter as the exhaust cam-cover oil-filler hole - about 2.5 to 2.6in

Are the cam-covers on E1001-8 studless, or with the three front stud holes, and is mass closer to 1.98kg or 1.38kg…

The C-type Spare Parts Catalogue lists the cam-covers for the ‘Production’ C-type as C.5889 (Inlet) and C.6723 (Exhaust) so the C.6723 is the same as used on XK120 from W.4691 (May 1952 onwards), but I haven’t yet identified the C.5889 which being a lower part number dates somewhat earlier but still a loose end given issue of mass and whether studless/or not, and no top-side protrusion ???

So to reiterate, Roger’s unmarked covers on the outsides appear identical to normal 8 stud covers in appearance and size, and are 43% and 59% above normal weights. This would have been achieved/caused by the 7 internal sand cores being smaller width and/or of lesser height than the cores used normally.
Possible explanations include:

  1. Defective sand cores, packed too loosely in the core molds, the resin mixed wrong or baked too long, etc.
  2. Pre-production samples or initial run with more wall thickness, later found to be excessive or unnecessary.
  3. From an alternate foundry

The fact of a boss inside with no corresponding boss outside for a C-Type breather suggests to this ex-inspector of foundry defects a core placement error.
An unknown factor is the abundance or lack thereof of these overweight covers. Perhaps there are more that have gone unnoticed by owners having nothing with which to compare weights.

On top side both Cam Covers look the same as C.2217 and C.2218 - so normal ‘studless’ cam covers, see pic…

But don’t forget their much greater mass (1.98 and 2.20kg) relative to C.2217/C.2218 at 1.38kg, so I would think a very deliberate new pair of castings, rather than just one of them being a defect…

Maybe an effort to make them stronger, given the propensity for these 1.38kg studdless cam-covers leaking from the front, and then cracking/breaking the stud holes when ham-fisted efforts try to over-tighten to stop the leakage. So time line/ and casting evolution suggest something after 1951 LeMans and before 1952 LeMans to me… so maybe a first effort to provide for a breather but still on the studless cam-cover, before refining design as per cam-cover now fitted to E1001 with raised/shaped platform on outside (also with front three studs ?) …


Are there any numbers at all?

It is possible someone had them cast up as spares??