First of all, my apologies to Maddy for practically “stealing” her thread about the gaskets to be used for the later carburettors and changing it into the subject of return spring(s) on XK 120 carburettors in general.
The many contributions however have lead to more understanding of what (may have) happened.
Although there are two “cranked” levers (Jaguar 1635 or AUC 3120) there’s only one Return Spring (Jaguar 310) attached (the lever of the Rear Carburettor).
We also know that the Mark VII changed over from one spring to two springs in the Autumn of 1952.
And at the start of production of the XK 140 in October 1954, the standard engine was more or less identical to the late XK 120 versions but now had a return spring for each carburettor. Jaguar changed the construction for attaching this Return Spring (Jaguar 310 and identical to the XK 120 version) by adding a separate Bracket C. 8015 positioned under the lower LH nut of each carburettors. As Rob mentioned already, these are the same Brackets that were added to the Mark VII in the autumn of 1952!!!
Roger P. made the remark that “later XK120, and thereafter, so all XK140/150 etc…needed a return spring for both carburetters.” Roger: do you also know whether Bracket C.8015 was used on these later XK 120s? It seems a logical assumption, but does anyone ever seen a picture of a late XK 120 engine with these Brackets?
Finally, it seems (still to be measured) that the length of Bracket C.8015 is shorter than the distance from the cranked lever to the screw of the strap of the starter motor. Furthermore, the bracket has two holes allowing to choose where to position the lower attachment of the spring. Both changes would compensate for the increased spring force by doubling the number of springs as Chris mentioned earlier.
Apology accepted but not necessary. The spring information is valuable in that I have to yet put my carburetors on and will need the return spring (or 2).
I will have more carburetor questions when the time comes and will continue the dialogue here.
Nope. You need to appreciate when an Australian was co-authoring a JCNA Judges Guide, I had to accept USA local knowledge of things I was familiar with based on Australian local knowledge. My immediate position was that XK140 introduced the two spring arrangement, but local Australian regulations required XK120 to add a second spring for safety reasons - and retrospectively, an XK120 was not considered roadworthy thus registerable unless modified to have a second spring. All the XK120s I had seen with two springs looked to me to be local modifications/non-SU parts etc, and I had not seen anything that looked factory original; but I suggested if I was going to modify an XK120 myself, I would replicate the XK140 arrangement, thus with a C.8015 bracket. But I was assured that ‘late US XK120s’ did have two springs, with the peer review consensus (all US local knowledge) that further research/evidence was unnecessary as it was an ‘acceptable safety related’ feature that was not therefore deductable. In Australia, we also allow two spring returns on XK120 as its a State legal/registration requirement, and we dont comment/care how it is exactly done, but expect with all appropriate period SU parts, and not some local speed-shop modern brackets/arrangement. So when Judging (in Australia) I would be happy if someone fitted an XK140 two return spring arrangement, or if they retained the quite different single XK120 spring arrangement and added a second spring return using period/correct SU lever/spring/brackettry…
But maybe someone has an extremely original late 1954 XK120, and can comment on whether one or two springs - I have photos of original XK120s as late as 5 July 1954 that still have their original single spring from a lever at rear of rear SU, extending down to the setscrew the holds the starter-motor cover in place… . See pic below… shows the rear-lever (original) and nothing on front throttle-shaft/SU
This seems to be one of those questions where we don’t have a definitive answer from the factory literature, so we have to stumble around and throw ideas on the table to see which one will fly.
The XK140 SPC at least has a picture.
Item 80 Bracket Anchoring Return Springs is part C.8015, also used on Mark VII, and it is a reasonable assumption that part numbers were assigned consecutively as they were designed in the engineering office, which is a high enough number to suggest that it was designed and the number assigned later in the XK120 era.
The wording in the Mark VII SPC might lead one to suspect that the two springs requirement did not at first apply to all markets.
However, Service Bulletin 128 June 1953 says they were putting two springs on Mark VII for more accurate slow running settings (and anti-creep setting on automatic transmission cars). Brackets for the springs were attached to the lower carburettor flange studs.
So I think we have a date for the bracket, May or June '53.
I did not find any other SBs mentioning throttle return springs.
Those of us with 120s with a single spring know that it is tricky to get the two carbs balanced together. Two springs would make it easier.
No 120 had an automatic of course, but perhaps they began putting them on all 140 engines because some of them did have automatic.
Just more ideas on the table.
An update on the use of 1 or 2 return spring levers on the XK 120/140.
Decided to opt for the 2 spring solution and thought that I could simply use two levers Jaguar C.5606 (or SU AUC 3120/1). But I soon learned that this Lever is too long and will touch the Thermostat Unit (AED). See photo below.
Both the Mk VII and XK 140 use this shorter Lever for the Return Spring on the Front carburettor (Jaguar C.6930 and SU AUC 1500/1, later replaced by AUE 180). This lever is straight (not cranked) and shorter than the (cranked) Lever for Return Spring of the Rear carburettor (Jaguar C.5606 or SU AUC 3120/1). The longer one AUC.3120/1 is about 1.5” between the holes and the shorter one AUC 1500/1 about 1”.
Note that Viart (XK 140 Explored) made an error and changed Jaguar part number C.6930 in an SU number AUC.6930. Idem for the longer version AUC.5606 which should read C.5606. Couldn’t find these SU numbers…
I took at look at the return spring lever on my front carb and, looking at it from the inlet side (opposite to your photo), it is cranked over to the right towards the idle adjusting screw and clears the starting carb by about 1/4". It is difficult to get a measure, but using a pair of dividers I got 1 1/4" between the holes, the same as the rear carb lever. If interested I will try and get a photo.
So you say that the “longer, cranked” Return Spring Lever does fit if it’s turned 180 degree. I will give it a try later today. Nevertheless Jaguar opted for a shorter Lever.
Had a try but the longer Lever doesn’t fit no matter how you turn it. You refer to 1 1/4" between the holes whereas the original longer version (AUC 3120/1) measures 1 1/2" and the Jaguar listed shorter version AUC 1500/1 measures 1". So I guess yours is yet another version (see list below) like AUE 191.
Found the correct Return Spring Lever AUC 1500 for the front carburettor which is indeed much shorter than the other lever AUC 3120/1. See photo. It’s now impossible for the lever to hit the Thermo Unit (AED).
Also found a replacement for the Bracket Anchoring Return Springs (C.8015) which is no longer available. The later version of such a bracket is fixed by using the 2 lower bolts of the carburettor. But it turns out that one “leg” is identical to C.8015 as used on the XK 140/150 (and possibly on later XK 120s). See photo. I will use a set-up with two return springs using two XK 140 Brackets.
To close this topic and for those considering to put a second Return Spring on their XK 120, I upload two photos.
The first one shows the front carb with the shorter Lever Jaguar C.6930 and AUC 1500/1 with the Return Spring attached to Bracket C.8015.This Lever won’t touch the Thermo Unit (or AED).
The second photo shows the rear carb with the longer Lever Jaguar 1635 and AUC 3120, also complete with Return Spring and Bracket. Note that on the photo 2 it looks like the Lever is almost vertical, but in reality it’s about 30 degree below horizontal.
I received the longer studs which I fitted them today. Before I do however I did have some crud in the forward most carburetor stud holes. I used some carburetor leaner spraying into the holes. Then I used cotton swabs into the stud holes to clean out the gunk.
My question is the gunk I cleaned out is it a precursor to bigger problems down the road? What am I looking at here?
That doesn’t look all that bad, compared to some. Really I would be surprised if there was none. Since this is a car that has unknown history, it is a precursor to the likelihood of having some gunk in the cooling system, and maybe having to do a flush after you get it running.
yes that is for sure some “gunk” but minor…I’d thread chase the holes carefully…and clean again…then some anti seize. As you have installed a new radiator…or will…it will be good to flush out the radiator…not unheard of to have something left over even in a new/rebuilt one…and try to flush out the engine coolant passages via a hose…from all openings…with side tap open( if it will) prior to radiator hose installs…not sure when you would get to the coolant part…winter is coming…but it whenever…it would be good once flushed, and when engine does run…to flush again with a Prestone cleaner…and water…before the more permanent anti freeze coolant is installed…if your shop goes below freezing…you want to be sure antifreeze is in the engine…not just unknown…or water. don’t forget the heater if there is one…
Nick
Hi Nick,
I cleaned those stud holes until they came out clean, not shown in posted images, and to thread chase as you suggested I would need to buy the tool. So skipping that part since the stud holes were clean and the new studs went in with fingers. Then I double nutted to tighten them up.
Before the Jag went into the garage for the winter I flushed out all the waterways. Opened the side valve too. There is no heater so no core to flush. When it is time for the radiator install I will run water through that to get any “stuff” out of it before it is connected to the engine.
I have purchased all my own tools to match what you provided me to do the valves. I did not buy a safety wire pliers yet. You could collect your tools next time you come this way. I am making slow progress and hope the engine will start this spring.
Bob,
I looked up that number C.8015 and get nothing in my search. I type in carburetor return spring y bracket and get two options: C15963 and C24736 which are brackets used on the e-type. So I am wondering if either of those would be appropriate?
Maddy
Rob,
I see. I’ll give mine a look. Life keeps throwing things for me to do making it hard to get to the garage! If I can get 1 day a week I feel fortunate these days.
Maddy
Further to Robs answer: I installed a second return spring to be certain that the front carb is also closing in a secure way. I decided to use the brackets that Jaguar introduced on the XK 140. However, as you found out, this bracket C.8015 is no longer available. So I modified the later version which has a “Y” shape. The straight part is identical to the original XK 140 part, so simply remove the side branch. See picture:
There may be other solutions to attach a second return spring to the front carb, but I decided to follow the route that Jaguar did for the XK 140 as the XK 120 successor.
sounds good Maddy…I think I left some safety wire pliers with you…since only a one time use. I will try to visit before too long and bring your spare and wire wheel. Nick
If you are only chasing threads to remove dirt, etc, you can make a decent substitute for a tap by cutting 3 or 4 longitudinal grooves along the threads of a bolt of suitable length. An angle grinder with a cutoff wheel will do the trick.
