New member, first Jaguar, intro and looking for advice

Hi all,
First a quick introduction - I never worked on a car before, and I don’t know much about engines, but being very technical in the areas of computers and electronics, this is something I want to learn.
I just got a 1954 XK-120 OTS into my garage so I have my golden opportunity.

This used to be my mother-in-laws daily driver until something broke and it was put in a barn some time around 1983. It’s been sitting under a pile of rubble ever since.
Some parts like the interior carpet has been eaten eaten by rodents, but after a good cleanup I think it is pretty good condition.
My plan is to make it mechanically sound so I can drive it, I don’t want it to be a museum piece.

The car seems pretty original. The engine block # matches, but the cylinder top has a different number (N something, maybe indicating it came from an Mark VII), so it looks like it must have been replaced at some point (but done in the 70s or earlier).

At some point someone mucked about with it so the distributor is in pieces and probably missing parts and the radiator was taken out and put in the trunk and the hoses and a few other parts lost - but I’m sure I have to get new hoses anyway.
The engine still has oil in it, and turns over with a wrench, so it seems like I should be able to get this thing going again.
Everything else seems to be where it should.

I’m taking this slow, learning before doing, and I’m looking for advice what to attack first.

Some initial ideas:
The car has two 6V batteries and positive ground. I’m thinking replacing the dual batteries with a single Odyssey PC925 as it seems that should fit in one of the bays.

Unsure about the distributor. Leaning towards a 123 Ignition for trouble free operation. I don’t know if the one I have is original and since it clearly doesn’t work without a rebuild maybe I should just go electronic.
I also need new cables and connectors to the spark plugs since they are cracked and broken off.

Take apart and clean out carburettors. Maybe get a rebuild kit and replace some of the internal wearables?

I’m guessing I should take out the fuel tank, maybe have it refurbished, or maybe even get a new one? and also get new fuel lines since these be old and crummy.

The break pedal had initial resistance, but when I pressed on it a bit, it let go and now goes to the floor with no resistance. There is no break fluid in the reservoir, so maybe look over the master cylinder and rebuild all four drum breaks.
I also want to test things like starter, water pump, fuel pump, generator, etc. can they be tested in place or should I remove them first?

Anyway, this should keep me busy for a bit, I spent the last year reading up on these models, got a few books on the subject etc. so I have a little bit of a plan, but I am in no rush and it would be great to hear opinions and recommendations from people more experienced than myself.

Last - here is a picture from a couple of weeks ago when I finally got it into my garage.


Looks good!
Might be well to have a knowledgeable owner visit with you to help sort things out.
Where are you?

I’m located in San Rafael, California.
Just a little bit North of San Francisco.

Welcome to the fun. All those items can be fixed, one at a time.
I would start with the distributor, fix the original like me if you can, new points and condenser and it will work fine; worry about 123 later if you can’t.
Plug wires can be bought as a set for '51-87 XK/XJ engines, or on a 25 ft roll.
No need to change the ground as positive works fine for me and I have a single 12V battery in mine.
For carb work you will need a set of British wrenches, and be careful with those banjo bolts because if they’re really stuck you can break the float bowls. There should be only one fuel hose from the firewall to the carbs.
Hoses and carb kits can be had from XKs Unlimited in San Luis Obispo.
Try putting some DOT 4 brake fluid in it and see if the pedal pumps up.
Water pump, just wiggle the fan and feel for wobbling, spin it and listen for worn bearings.
Starter, just try it in place. There is a big button on the back of the solenoid you can push to test it.
Fuel pump idle that many years might need a new diaphragm and points, possibly a clean out, so better to do all that on the work bench.
Maybe that’s what broke in the first place?
Generator may be ok or just need cleaning the commutators.
A head with serial number like N(ABC)1234-8 would be from a Mark 7/8/9.

If I were a computer and electronics guru, I was starting from scratch, and originality was of no concern, I would seriously look at a distributorless EDS ignition system. There are some guys on here who swear by them. @Wiggles I believe is a knowledgeable source on the topic.


Hydraulics/Brakes: the most important safety system… I would remove and rebuild the entire system down to the last bolt and washer, replacing all flexible lines. Flush all hard lines with alcohol. I would take that opportunity to convert to DOT5 fluid. Conventional brake fluid means regular PITA maintenance. Make sure the rebuild parts are confirmed to be ok with DOT5.

Distributor: I would replace everything with modern components (Pertronix Distributor, modern suppression core wires, NGK BPR6ES plugs). You can have your old dist restored and keep it as a spare. Multiple friends with 123 distributors are having oil contamination failure every 5-10k miles due to a design oversight on the shaft. It’s not a problem as long as you plan on having it rebuilt before it leaves you stranded.

Fuel/Carbs: disassemble, clean, check. Tank: remove it and clean/replace. Replace the sender while you are in there and use a new SS type f-pump from John Brady, and add a modern filter upstream of the pump. You can restore your old one and keep it as a spare.

Cooling: while I like authenticity and originality, I put a HD three row conventional core in mine, and overheating is a thing of the past, even without an electric fan. I think I hit 95F on the gauge once on a 98F day in a 30 min long traffic jam. But an elec fan is a smart upgrade. Things like an alloy external pressure tank and aluminum radiator that the big suppliers sell seem like totally unnecessary expenditures to me.

Nobody has mentioned it yet but before you touch anything, go online and buy basic Whitworth/ BSF wrench and socket sets. Also a 1/4BSF and 2BA taps and dies at a minimum. Keep them separate from your other tools. You’re going to immediately find that standard SAE/ metric tools are either too loose on the fasteners or, just a little too tight to fit. That’s your clue that you’re equipped with the wrong tools. And cheating via overuse of a Crescent wrench not only advertises “Amateur here!”, but has the potential for rounding off bolt heads/ nuts and is universally frowned upon. You’re going to be spending a good chunk of change on your car so, might as well equip it with the right tools from the get-go.

Does it still retain its original tool roll?

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Would strongly recommend you put in a new master cylinder rather than rebuild the old one. My experience with rebuilding old ones is that it is less than 100% successful, even though it has been done successfully many, many times by many many people. the risk is just too great to fiddle around with it. You have to take the cylinder out anyway and it’s not free to rebuild it. Put in a new one.

The cylinders at the drums seem to be OK to rebuild. There are six of them on the car, so if one isn’t working, you can still stop just fine.

Also. Take a lot pictures of everything before you start taking anything apart. You will need these down the road.


Helpful for the chassis and gearbox, but there are virtually no Whitworth fasteners on or in the engine, maybe one, IIRC. Everything there is mostly UNF with some UNC. BAA for the carburetors. Your fractional hand tools will be fine for engine work. And because it comes up all of the time, you might want to consider a shallow 1-5/16" socket for the crankshaft damper bolt.

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By the way… we’re all jealous.

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When I wrote this I was thinking specifically of the valence panels on each side of the engine. I can’t imagine going deep with an engine resuscitation without removing these. It makes things so very much easier – at least in my experience. Lower radiator hose? Piece of cake. Changeout takes five minutes. Starter motor, master cylinder, distributor, manifold/ header pipe nuts, underside of carbs – all so much easier with the valence panels out. And removing all of those rusty, encrusted 1/4 BSF fasteners will be an exercise in frustration without the correct tools.

Mike, aren’t many of the brass fasteners on the SU carbs BSW (damper and jet cover/assembly)?

There are other places on an XK120 where BSW sockets and wrenches are useful.

Cliff, did you try rebuilding with an NOS seals kit?


Thanks everybody for all that great advice!
Reading through this several times, and thinking about it more, I think I need to prioritize in order to not feel completely overwhelmed.
I have also decided to not try to modernize or modify things without trying the original first.
Thus, first order of action will be:

  • Distributor - rebuild the original one which I think is the original for the car. Provided I can find parts I need and figure out how it fits together.
    Get new ignition wire and build a new ignition cable harness. Spark plugs too, of course.
  • Install a new battery and check electrical system for shorts. The battery cables looks pretty cruddy, so maybe install new ones.
  • Carburettor cleanout, maybe a rebuild kit?
  • Remove and clean out gas tank / replace gas lines
  • New fan belt as the existing one is crumbling
  • Toolkit / tools

So basically whatever I need to get the engine humming feels like a good place to start.
I will worry about breaks and other essential systems once it starts up.
For the toolkit, I actually haven’t checked if the original kit is in there. I saw the red jack and a couple of Thor hammers in there, but didn’t remove the spare tire to see if there was something else hidden in there.
Anyone have recommendations for tools? I seem to be confused between threading and head size. It seems the threading standard has an impact on the head size (thus tools), which was new to me. I don’t mind spending a bit on tools, so if there are essential things I need to make life easier I’d very much like to hear. Does any “Whitworth/ BSF wrench and socket sets” kit cover it, or should I look for specific sizes to make sure I’m covered?

I haven’t really removed anything yet and once I understand what ‘valence panels’ are, and how to remove them, that sounds great - thinking removing the hood will help too.
So far, most of what I need as far as parts go, seems to be available from, so that’s good news.

Thanks again everybody!

SHHHHH!!! You’ll wake up @ptelivuo!!!


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Yes, some of us are jealous of a rust-free black plate California car.
As you can see, there is a lot of expertise here, and even some contrasting opinions. :upside_down_face: But we try to be friendly and helpful and since 1993 this forum has always been about giving accurate information.

British Standard Fine aka BSF is a thread system used on older British cars, and on the XK120 is found on the body fasteners, gearbox, rear axle, rear shock absorbers and most electrical parts. The sizes marked on the wrenches refer to the bolt thread diameter, not the hex size.

British Association or BA is a set of smaller thread sizes found on electrical parts, and the socket sizes are 2BA, 3BA, 4BA etc.

British Standard Parallel Pipe aka BSPP thread is another thread system for fluids, and is found on SU carbs, SU fuel pumps, fuel tank and fuel piping, and water fittings on the water pump and intake manifold. They use the BSF wrenches.

England was making the transition from BSF to the SAE thread system of the USA in the 1940s and 50s, so newly designed things like the XK engine and independent front suspension and hydraulic brake system are SAE threads, and you may see red bolts as an indicator of SAE thread, though in some cases the hex sizes were still BSF sizes.

So you’ll want to get a set marked 1/4BSF through 9/16BSF and 2BA through 4BA.
I don’t recall any metric threads at all on an XK120.
And if you have a broken bolt you want to be sure not to substitute the wrong thread there.

I forget if anyone has already mentioned the factory Service Manual and Parts Catalogue, which are excellent essential items and can be had as reprints or on CD-ROM.

You mention battery cables, and if they are the original helmet type with a little screw in the center, you may want to try to clean them up and save them, or at least don’t throw them out. But drilling the lead battery terminals for a screw is a tricky job with the possibility of broken drill bit if you go too fast. But it does make a good connection if you do it right.

Gas lines are copper so usually last indefinitely, so you may need to just replace the rubber flex hose going to the carbs.

Carbs are likely to have old dried up gas and crud in the bottom of the fuel bowls. Use penetrating oil on them before you try to loosen any bolts.

Better not take off the hood (aka bonnet) unless you really need to, because it can be tricky to realign the hinges putting it back on, but you can get a broom stick and prop it up higher than the regular stick if you need to.

Here is mine with the right valence panel removed. I was replacing the wiring harness at the time.


Do the engine last. Internal rust will set in when the engine sits for a prolonged period. If you do the engine and then do everything else; you may find, when ready to drive it, that time has undid all the work you put into the engine.

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Welcome to the forum and congratulations on your new project! The comments above, which contain some invaluable advice for bringing your treasure back to life, show you’ve come to the right place…

I don’t want to throw cold water on your enthusiasm, but you’ve picked a very challenging project to learn on. While these cars are fairly simple from a mechanical standpoint, they do require quite a bit of knowledge, skill, and money. And the less you have of the first two, the more you need of the last one.

Even if nothing is “broken”, every system on your car is going to need a thorough going over. If it has indeed sat since the 80’s every rubber bit is sure to be hard as a rock and need replacing. This includes everything from the rubber diaphragm in the fuel pump and rubber brake lines, to the entire suspension system.

Anything with fluid in it needs to be flushed, cleaned, inspected, and refilled. Expect to find a few leaks.

The brake system is arguably the most critical, just in terms of safety alone. Hydraulic brake fluid absorbs water over time, so in addition to rotten brake lines, you’re sure to have corrosion in the master brake cylinder as well as each wheel cylinder. Depending on the severity, the cylinders may require more than a simple rebuild kit. Unless you’re familiar with rebuilding and bleeding hydraulic brakes, I agree with the advice to simply replace for safety’s sake. This is one area where you should have someone with experience to help you.

And speaking of experience, probably the single biggest thing that will aide you in your project is to join your local JCNA chapter. Go to local events, meet members in your area with these cars and learn from them. At the end of your project, they can help ensure you look back with pride instead of regret.

Good luck, and remember: photos or it didn’t happen….

Hi Chrutil,
As you queried here is a photo to highlight a valance.
As well as taking photos from every angle as you dismantle, put every piece you remove into a plastic bag and label it. Don’t throw anything out.
Don’t set any deadlines, that way each job will be done thoroughly without having to take short cuts.
Good luck,

so cool…a Calif car…tell us more…so much said by others already…but also…spend some time in the archives of this forum…use the magnify lass at top right…select for XK, then type in whatever topic…try a lot…and you will find tons…and you can copy, paste…and print, and put in a binder by topic…also a few very recent posts from another who just got an XK 120. It appears on the posts menu as it is recent…for Maddy…and another “new”. For the distributor rebuild…I highly recommend British Vacuum Unit…in the East…fine job on mine…all stock…which is my preference as I can do points and time, any time easily. These cars are amazing…I have seen many that sat for years…start up with just the usual normal precautions and prelim "to do " list. When you do whatever with radiator…chec on this forum archive for Thermostats for the X Ks…as it requires a special type. Nick