Thanks Roger–did not look in the SPBs–there it is!
some pics of various pistons and factory and technical drawings
3.8 9-1 part number is 14541. (1)
3.8 9-1 part number is 14541.
18394A (1)
18394A (5)
18394A (8)
18394KR (1)
18394KR (2)
18394KR (3)
AE 83 mm pistons (1)
AE 83 mm pistons (2)
AE 83 mm pistons
C13794-1 9-1 (1)
C13794-1 9-1 (3)
I have one of the 9:1 XK140s as well. My pistons look like Phil Dobson’s photo. They are not flat at all. The “flat top” protrudes upwards into the combustion chamber. It’s very similar to the Chrysler Hemi pistons (pic attached).
Dave
Sorry, to avoid confusion, the picture is from a Chrysler Hemi engine, simply meant to demonstrate how similar the pistons are.
Dave you are right and perhaps a poor description but in the world of Jaguar XK engines that is an apt description as all others are dome shaped.
Given 7:1 cr pistons as fitted to MANY MANY 1950s XK engines (if you live in the colonies, or in Asia, that then had poor quality fuel), are 100% FLAT, I personally think it is totally misleading to refer to 9:1 pistons with valve cut-outs as being ‘flat’
Indeed virtually 100% of XK120s, many XK140s including a number of XK140MC, had FLAT top 7:1 cr pistons when new. So numerically, far far more XK120/140 world wide with flat-top 7:1cr pistons, than had 9:1 pistons, whether domed-top or semi-flat with valve recesses.
Need to come up with another name for the 3.4 litre 9:1 pistons.
Without trawling through things – do we collectively yet have a view whether the very rare XK120 and relatively rare XK140 with 9:1 pistons, use the same piston as the relatively common 3.4 litre XK150S 9:1 cr piston? And do we know what piston was used (re 3.8 E-type style domed, or 3.4 litre style semi-flat with valve-recesses) in the relatively rare 3.8 litre XK150S (that I think were probably all 9:1 cr.)
Bora – do you have a photo of your XK140 9:1cr pistons, rather than what you say are look-alike Chrysler pistons, which seem to be domed with a flat top, and valve recesses!.
Roger you may be right–remember I am in the US which accounted for 75% or so of the production. We have never seen a 7 to 1 in anything. Perhaps another name is proper for the pistons but the initial question was about the ‘S’ pistons–thread drift I guess
We know we know.
Even England got mostly 8:1 cr XKs, it’s just in this post-war period, through the 1950s, fuel-quality in Australia, New Zealand and nearby SE-Asian countries buying Jaguars – mostly ex-pat Brits in Singapore, Malaysia, Hong Kong, India etc, pretty well standardized on 7:1cr XKs and Mark VIIs but gradually improved so by XK150 8:1 was the norm. But even XK150S and 3.8 E-types where UK, Europe and USA now got 9:1 as standard, we only got 8:1 as standard, with 9:1 a special-order, thus rarely see a pre-E-type, 3.4 litre 9:1cr piston!.
But in the 1950s only those racing with ready-access to Aviation-Gas used 8:1 and indeed occasionally 9:1
The only good news now though is most of these 7:1 cr XKs when it comes to engine-rebuilds, throw out their 7:1cr Flat-top pistons and upgrade to 8:1cr domed-pistons, and only other mod required is distributor re-mapping.
But yes, when thread first raised, that is why I immediately said FLAT top was a 7:1cr piston.
Isn’t that what a part number is all about? The term “flat top” was first put forth by Jaguar. Why reject that? If 8:1 and 9:1 are both “domed” do we need another name for one of them? I’d like to work backwards and identify C7710 solid skirt and C10649 semi-split skirt pistons. In August '51 “the Autocar” stated that 9:1 pistons were available. The C7710 racing pistons appear to have been cataloged close to the time of “C” head C7707. I thought it was about "53 when Jaguar first offered that. The Brico 9:1 piston is semi-split so clearly different.
below is a list of part numbers
C7710 3.4 8-1 racing pistons
C.10649 3.4 9:1 cr semi-split skirt pistons flat-top see Service Bulletin B.3 Spares Bulletin A.33 of April 1960
C13794-1 9-1 ?
C14541 3.8 9-1 ?
C14806 3.8 8-1 XK150S
C16339 3.4 9-1
C26637
C26638
C33088 4.2 9-1
C.34679 is a 1976/7 part number
C38295
18394A (1) 3.8 litre 9-1 Hepworth/AE part number replaced 16891
18394A (5)
18394A (8)
18394KR (1)
18394KR (2)
18394KR (3)
Uploading…
Is that standard or + 0.010" Terry?
there is a picture in XK140/150 in detail by ADC page 93 showing a 7-1, 8-1 and 9-1 piston alongside each other noted as JDHT pic so possibly a period photo
the 8-1 and 9-1 are both domed
now here is a factory pic of a high compression piston but which one
34204 written on top
Possibly a competition piston considering source of photo
just found a pic of a C23510/1 so we can add this to the list
That picture looks like the .040"-over Mahle racing pistons that had been installed in my 3.4 MK1 by the previous owner. I noticed how they didn’t simply take up space in the combustion chamber but actually created a new, smaller chamber at the top while effectively filling up the rest of it. I was never told what the actual compression ratio was (only “high”) but the engine only ran on Sunoco 260 or American Super Premium. A compression test yielded results in the 210-220 psi range. During the gas crisis in the '80’s I took the head off and added a couple of extra head gaskets so I could use whatever brand of gas was being sold that day.
just found another piston C12098/2 and also C5724
C5724 Piston High Compression 9-1 Aerolite date 6 june 1951
C7710 3.4 8-1 racing pistons
C10649 3.4 9:1 cr semi-split skirt pistons flat-top see Service Bulletin B.3 Spares Bulletin A.33 of April 1960
C12098/2
C13794-1 9-1 ?
C14541 3.8 9-1 ?
C14806 3.8 8-1 XK150S
C16339 3.4 9-1
C23510/1
C26637
C26638
C33088 4.2 9-1
C.34679 is a 1976/7 part number
C38295
18394A (1) 3.8 litre 9-1 Hepworth/AE part number replaced 16891
18394A (5)
18394A (8)
18394KR (1)
18394KR (2)
18394KR (3
