I’m not finding this in my '120 parts catalog. Usually it’ll reference up to a certain engine number for one and then continuing with another. Was it a matter of using up old stock before going with another but not documenting it? Just curious. Thanks.
They were special order for racers from about June '51 according to Service Bulletin 95, then as an option with the SE package from about Sept '52 according to Service Bulletin 109. I did not find a reference for when they became standard on 120, but they were standard on 140 and became standard on Mark VII in Feb '55 according to SB162.
Rob is correct, there is no quoted chassis number change as both the original 5/16" lift camshafts - C2237 and C2444 - and the ‘special order only’ 3/8" lift camshafts - C5717 and C5718 - remained available in parallel up until the last XK120 built in 1954.
As Rob advised, the C5717/C5718 was offered as an aftermarket spare part from about June 1951 onwards, but was then the standard factory fitment for all XK120SE cars as denoted by engine number having an -S suffix to engine number. Standard XK120 continued to be fitted with C2237/C2444 camshafts up until the end of XK120.
Both standard XK120 and XK120SE still used the same A-type cylinder head, with just the camshaft upgrade (and exhaust valves) primarily responsible for the quoted 160 bhp (of a standard XK120) to the 180bhp of the XK120SE.
In USA, later XK120s were predominantly the upgraded XK120SE, but in UK and Australia, standard XK120s still outnumbered XK120SE to the last. Indeed in Australia, most XK120s were built/delivered with 7:1cr engines as our 1950s regular pump fuel could not support 8:1cr, albeit 7:1 was only worth about a -5 bhp loss.
Also there were precautions in the Service Bulletins about fitting 3/8 cams to an early head, such as machining off the ends of the valve guides, chamfering the tappet guides, etc. which should be examined if you are contemplating this change.
I think I’ve only seen one block with 7:1 flat top pistons here.
SB105, April 52 refers to factory modifications to the cyl heads starting at engine W4483 that allow for the fitting of a 3/8 cam without further modifications being necessary. Prior to W4483 a cyl head/tappet guides will need very important modifications (unless a prior owner already did them). SB129 Au 53 refers to "engines produced with hi lift camshafts (for special equipment models) " then info on springs, and this seems to infer that still just the SE with the hi lift cams. SB142 Jan 54 refers to precautions for fitting hi lift cams and lists the XK120 C, the Special Equipment models, and…“Mark VII and XK120 cars fitted with high lift camshafts in service”. This “in service” would seem to infer that other than C and SE…the hi lift was not fitted in production. SB149 May 54 deals with camshaft/valves but does not have to do with the topic of any factory cam change. This leads me to believe the 3/8 was never standard from the factory in the XK120 except in the SE when it was standard. What happened next in The 140 era is in the realm of researcher Roger Payne. So…prior to W4483…modifications are needed if fitting a 3/8 to what had been a 5/16. After that…still pay attention to the many various precautions and changes in tappets, springs, guides, stems, valves etc thru production, that all must “match up”.
and…a request…Please…if you have a camshaft…any XK, or Mk7, where you can see it, access it…I would like to know the measurements heel to lobe, side to side off lobe, and the C part # on it,. Info to be shared later, thanks.
Nick
Okay, a big thanks for this information. This helps me out. I’m weighing whether to have my current, non-original head rebuilt vs. the purchase of a rebuilt “studless head” being offered by a local Jag club member at a very fair price. A studless head would be more appropriate for the year of my early car, but at the cost of just 160hp. My current head (W5113-8) has the 3/8" lift and thus, higher horsepower… The rebuilt head maybe not – I have to ask about the cams on it. It’s number is W2- something so it probably has the smaller lift type. Decisions. Decisions.
so for your decision…may also depend on how you will drive the car…will you notice a small HP difference? and BTW…not all was just the cam lift…so depends what else was rebuilt in your engine over the years, what pistons,is compression good, is it a true dual exhaust all the way, some perf is gained in…modern fuels, a distributor rebuild that modifies the mechanical and vac advance, modern spark plugs, what is your diff final drive ratio, and more. I too have a non original cyl head on the car…in very nice cond and tune…but with 5/16 cam…when the original, now lost in time-space (W7902 anyone?) , was a SE 3/8, and I have a spare head closer to original number…but still not original. It may be that the W2xxx has not had the mods…or maybe it has…you’d need to see and ID the cams,…and also the upper edges of the tappet guides which have to be chamfered etc for a 3/8 to fit…as per the SB105. Much could…or could not have been done over the many years/owners. Nick
I think everything I have at hand falls outside the desired part numbers (some difficult to read), but here they are:
C13081 - 2 bolt flange, drilled heel, 1.044", 1.425", (probably 1959 3.8L MK9)
C13080 - 2 bolt flange, drilled heel, 1.044", 1.425", (probably 1959 3.8L MK9)
C14985 (exh), 2 bolt flange, drilled heel, 1.044", 1.425", (1964 3.4L MK2)
C13081 (int), 2 bolt flange, drilled heel, 1.044", 1.425", (1964 3.4L MK2)
and for giggles, 3 modified camshafts:
stamped 4488 - 2 bolt flange, (marked 220/320) (int), 0.958", 1.27"
stamped 2237 - 2 bolt flange, (marked 226/328) (exh), 1.004", 1.323"
4 bolt flange (int) 0.976", 1.364" (S3 XJ6 4.2L)
thank you.I .will collect, collate…share later…those are interesting., so will see what the car/engine application was. Even with same 3/8 lift, or the 3/8 some profiles of open/close duration did change. The Factory Manual did state that for the Mk 7…early…that was 10 50 57 15…but with 004 006 clearance, whereas the XK was always 15 57 57 15. and at first 006 008,. I won’t know much about duration from this data, but will try to find out. Nick
Christopher,
Your biggest decision that matters is which head you want to use, and how fussed you are or not re authenticity.
If your car should have a ‘studless’ head, and the studless head on offer is in good/rebuildable condition then that’s your best choice. It doesn’t matter what cam shafts are in the head, as if already 3/8 lift that is your preferred 180bhp spec (depending on exhaust valves), but if only 5/16 lift; you say your W5113-8 head already has 3/8 lift cams - so use those in the studless head. You don’t have to worry about finding part numbers on cams - simply get a caliper and measure the two relevant diameters, and that will quickly tell you if they are 5/16 or 3/8 lift. As has been pointed out, if fitting 3/8 cams to an earlier head for the first time, as per the Service Bulletin you will need to machine clearance for the cams on your followers.
If you are fitting a used head, then it is false economy not to do a full reconditioning of head, and indeed if you use a competent/experience Jaguar head machine shop, then they can attend to your valves and camshaft fitment as part of the job. But the main thing is - make sure you do use a competent Jaguar head machine shop, as if no experience in XK heads there are traps for non-experienced machine shops, and the last thing you want is someone ‘learning’ on your head. Ask around, who is recommended for XK head work that does a professional/competent job, and at a fair price. I am in Canberra where we have access to several engine machine shops, but I still send heads to a place in Melbourne - 650 km away, but cheap enough freight overnight, more than made up for being ‘the best’ in Australia, and a fair price, and have done hundreds of XK heads and stock all the top quality parts needed - new valves, guides etc etc.
Re Power ratings - in the 1950s, Jaguar quoted ‘gross SAE power’ which by modern standards is very overstated relative to modern preference for ‘net DIN power’; but regardless, the relative SAE gross ratings are real enough.
AS before, a ‘standard’ XK120 (all have A-type heads, 5/16 cams) is 160bhp (SAE Gross)
An XK120SE (all have A-type heads, 3/8 cams) is 180bhp (SAE Gross)
A ‘standard’ XK140 (all have A-type heads, 3/8 cams and are identical to XK120SE head assembly) is 190bhp (SAE Gross), with the extra 10bhp I believe to be a result of the much improved XK140 Inlet Manifold design in conjunction with the much improved cooling system design that flows through the inlet manifold)
An XK140MC (SE with C-type head) - has of course a revised ‘production’ C-type head, and the same 3/8 cams, giving a 210bhp (SAE Gross), with the extra 20 bhp totally attributable to the revised/improved C-type head.
XK120 owners in 1953/54, could of course buy through Jaguar spare-parts outlets pre-production version C-type heads, and replace their standard A-type heads, but that was rarely done and invariably for only those who raced their XK120s so usually had other modifications as well when road-use refinement was not a priority. Once the ‘production’ C-type head became more readily available with the XK140MC from October 1954 onwards, many XK120 owners then had access to second hand XK140MC heads.
I would note that if your original engine had the 8 stud (studless) cam covers and the head you have available is the later 11 stud variety, the earlier cam covers can be fit to the later head by removing the extra 3 fixing studs. You will have to sort out the tachometer drive, which will be a little different.
This is a straight port head from an early 420 with the early 8 stud cam covers in place.
