I have a set of Brico pistons with a number M1670/1. I don’t see a Jaguar number on them. They are flat top 9:1 probably from a 150. Can anyone tell me if these are Jaguar pt # C 10649?
art
Don’t know how flat tops could be more than 6 to 1 or so due to the hemi head’s huge combustion chamber…from ~98cc to ~104cc is what I’ve measured.
Jaguar flat top pistons for 3.4 and presumably 3.8 XK engines were 7:1 compression ratio.Commonly seen in Australian XK120’s and sometimes in XK140’s when fuel quality was marginal, and not considered sufficient for an 8:1 engine, as standard in UK and North America.So surprising to see now in USA.8:1 pistons have a semi-dome top, and 9:1 pistons a full dome top - originally, but who is to say what may be offered today from the Indian after market offerings, albeit Brick is a good brand…
Roger perhaps he is describing the 3.4 S 150 piston that does have a flat top but on a ridge with two valve reliefs.
150S is pretty much a given here. None of those would have had 7 to 1 here. As George says these have the relief on the sides for the valves. No way are these 7 to 1s. The full dome 9:1 config came a bit later. All here are 3.4. I think all 3.8 9:1s had high domes. Time wise it looks like the 9:1s went from flat to dome about time of 3.8 introduction. But I clearly remember my friends having flat tops in their 150S engines. Those people and cars go back to the late 60s. Two of these pistons came from one of those people. Maybe the box of 6 also if he did a rebuild. No chance these are any newer than 40 years old. I’ve had them that long.
art
Yes. Thank You. I see them as 150S pistons but I think some people have been calling then “D” pistons.
I do not believe these are anything like the 9-1 pistons fitted to an original XK150 ‘S’ or for that matter any XK150 3.8 or MKIX?
Thank you Phil. I see that sample is .040. The ones I have are all letter grade G. What I’m really looking for is a Brico (not Brick) reference list. Or a known example of C10649 labeled as such. It’s very hard to find anyone who has any actual hands on experience with these.
Terry they sure look correct to me but I have only restored 5 XK150S cars. While it is just a picture and not a factory issue the 5 sets I have seen were very much if not exactly like the one shown.
Terry please see Technical bulletin B.3 dated May 1960 which says in part for 3.4 XK150s and 3.4 XK150Ss that: “On cars with above engine numbers… 9 to one compression ratio pistons with domed crowns are fitted REPLACING flat top pistons”.
does it give a part number for the new piston in B3?
I have a few pics of pistons from jaguar motors see attached. I would be keen to know what the piston C34679 was originally fitted to.
Certainly the 9-1 XK140 pistons have a std dome top
1 Like
A 5 digit number starting with 3 is way out of line for that point in time. I expect E type pistons to be C16339. The C10649 could be had for $19.08 in '59 according to the price list. I have never seen a 140 fitted with original 9:1 but it is possible. I would expect to see that as a suffix on a “C” head.
Certainly more to be discovered on this.C.34679 is a 1976/7 part number, and indeed in a Series 2 XJ6 parts catalogue I have 4.2 and 2.8 pistons of high and low compression ratio have part numbers around but not exactly C.34679, but no listing of the then UK market only 3.4 engines so a guess, that may be it??? But I seem to recall XJ series 2 high compression pistons were 8.7:1 cr, not 9:1. Not overly inclined to wade through all my 1970s literature to be any surer. Certainly the illustrations of 4.2 pistons look exactly the same flat-top with valve cut-outs.
Certainly Service Bulletin B.3 of May, 1960 quite clearly quotes: “On cars with the above engine numbers (XK.150 3.4 litre - V.7524; XK.150’S’ 3.4 litre and 3.4 litre Mark 2 - KG.2807) and onwards 9 to 1 compression ratio pistons with domed crowns are fitted replacing flat top pistons.The domed crown piston (Part No. C16339) can be used to replace the flat top piston (Part No. C.10649) can be used …”
(I would scan and post B.3 but we are in middle of a power outage, so no working scanner)
I don’t have any reference to 9:1 piston part numbers as rarely used in XK140 and XK120 - but they certainly exist.
Roger
Seems original ‘flat-top’ 9:1 cr pistons only applies to 3.4 engines, and not 3.8 nor of course 4.2 so of no relevance at all to E-types. Even if flat-top pistons were reintroduced in late 1970s for both 3.8 and 4.2 engines, they may work OK if installed as sets of six, but I think I would rather stay with original dome-tops.
Certainly love some good photos of original 1950s 9:1 flat top 3.4 pistons.
93 9-1 compression XK140 motors were built and fitted to cars with no total rhyme nor reason ie cars that had them were not necessarily raced. I am lucky enough to have one of these engines for my XK140 roadster.
A set pulled out of an Australian delivered 9-1 XK140 certainly had a dome top to them they were reused in an engine rebuild and were subsequently removed on a second rebuild.
Roger take a look at B.1 and see if that helps.
Text is from Chuck Hutchinson in Baltimore area. With permission
" Definitely agree w George and Phil the 150S had 9:1 flat tops w valve reliefs. The odd 2 you have may have come from me as I had to replace 2 originals I had melted due to a broken spring in center carb on a very high speed (125+) run between Chicago and Omaha in late 1969. I bought 2 aftermarket pistons but they were 28 grams overweight from the originals and couldn’t be lightened enough to work. Art came to the rescue by sourcing 2 used originals from someone he knew who was rebuilding his engine but had to bore out. They were within 1 gram of the rest and worked perfectly. "
George, I don’t know if B.1 really helps that much - its not descriptive.
Not like B.3 that clearly advises 9:1 cr pistons were definitely originally flat-top (with recesses), before being superseded with more familiar dome-top pistons - presumably improved design by the requirements of the late 1950s.
But have copied B.1 as below for those without access:-
But also in Service Bulletin B.3 it references Spares Bulletin A.33 of April 1960, which very clearly advises that the earlier 9:1 cr pistons Part Number C.10649 was most definitely flat-top, and now replaced with C.16339 with a ‘Dome Crown’.
