Mystery nut in the sump, 1969 XJ

Hi all,

I‘ve found a nut in the sump and I have no idea where it is from. It does check all the boxes but I‘ve not seen anything like it before.

The circles we all know and the P‘s are for the strength rating. So it is British and from a car that lived in France.

It’s 7/16“. Any ideas?

I also found a little spring but I need to find it again to take a picture.


Looks like one of the cam cap nuts: maybe someone dropped one, and just found another one! Seen it before.

The spring may be from the upper timing chain adjuster plunger?

It isn’t. Too small. Also mine are not marked and all identical. But I‘ll look again.

No, the spring is very small and only has 2 or three turns. And it is smaller in diameter. It’s ‚somewhere safe…‘ but as it‘s the tiniest spring I‘ve seen outside of electrical switches. Good guess nevertheless, thank you.

Does the lower timing chain tensioner have any nuts, or something around the distributor?

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Neither have I, David - does it have inside threads?

The only nuts with a legitimate right to be within the crankcase are the big end bolt nuts. Obviously any nut may unscrew, so inside nuts are kept at a minimum…right?

xj6 85 Sov Europe (UK/NZ)

C’mon Paul, it happens to all eventually
I s’pose, memory fade that is😢cam c

ap nuts being 1/2”AF n’all ! :grinning:
Perhaps one of these nuts @ 7/16 AF.

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The spring is actually not a spring but part of the ignition leads. Where the terminals screw into in the cable itself. Thank you for guessing.
So that one is solved and I will look at the chain carrier tonight.

Maybe they dropped the nut and replaced it. It only has 44k miles so if true it’s likely a factory error. Monday car? My cam bearing caps are numbered 1 2 3 4 5 7 6 8. I think it’s very likely from the carrier. promising!

Hehehe: I missed the info in the OP of the nut being a 7/16": you may be correct, re: it’s origin.

When you say 7/16" or 11mm you mean across the flats, so it would be a thread of 1/4-28 UNF. How about the oil pickup tube?

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Locking nuts are used on the brackets that hold the pickup / delivery pipes
Rob, the one shown is plain.

Ah, ok, I am not that familiar with the XJ, in my 120 they are plain nuts with lock washers.

Yes! Those nuts are identical. Everything is there so it got replaced. Thank you! And of course to everyone else as well.
Yes, the pickup tube has nice locking nuts but is looks like it would fit the threads.

Solved now.

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So you can put a “nut 7/16” 1/4-24 UNF NOS" on ebay - 51 years old and always well-kept in the oil pan of a Jaguar!

Aren’t these cars just great? - Who knows which other parts we’re driving around without even knowing? And how cool must these workers at the conveyor belts have been back in the days “Ahhhm, sorry Pete, seems I lost a nut down here …” - “Where about?” - “About here … maybe …” - “What did it sound like?” - “Uhhh … like ‘ding-ding-a-ding’” - “Don’t worry, mate! It’ll find its way to the oil pan … maybe someone will find it in a few years and wonder what it is … bruhaahhh!”

Only this summer I started filling a box with strange parts from my cars. Up to now I only have collected witnesses of disaster like gearbox caps shorn off or horrible attempts of bodging a pressure pin for a slave clutch cylinder. An original bolt from the production line would probably make it on my desk.

Good luck and keep up the work, David!


75 XJ6L 4.2 auto (UK spec)

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If you’re interested you can have it - I have way too much memorabilia too.
But I’ll hold onto it until the car is running, we all know about the obligatory nut that stays behind.
(Actually, it’s likely the nut engineers design in for later cost and weight savings anyways)

I think the nut has been used with a lock washer before given the circular trace. But the assembly was all over the place with different bolts mixed together, whether on the oil pump or behind the battery, so I wouldn’t be surprised. And I’d have done the same on the line. How large is your box?

Today I cleared the mouses’ nest behind the brake booster. I like the mouse that lived there once, clean, organized and she kept the service tags… can’t be mad about the bonnet liner.

As the thread has transcended somewhat anyhow … isn’t it just proof of a symbiotic existence between a Jaguar, a mouse and the owner;-)

And good to see the oil changes have been made in such short intervals!



75 XJ6L 4.2 auto (UK spec)

Yes. It still broke though, with less than 70k on it…
But overall it has been well maintained by the owner and mouse was clean too, no droppings or bones.

Do you know what gave? If you’re lucky and the car was stored well you got a low mileage engine with limited engine damage lending itself to minimal invasive repair instead of full rebuild …

Good luck


75 XJ6L 4.2 auto (UK spec)

Back when we exchanged a few messages on the S1 I sent you a picture of the broken piston. Well, the block‘s now near Aalen, for resurfacing, a hone and boiling out (they sure take their time but they have the machinery and do interesting engines), the head is ready and the crank has clean sludge traps. Two pistons were seized ans one didn’t respond to the Very Large Hammer™ so I had to resort to chiseling it out. All great fun though.

What’s left to do is new pistons, check rods, assemble, test run, put it back; new exhaust and new brake fluid, brake discs and the other front wheel moving parts. Then off to TÜV I guess and I‘ll be driving some time next year!
Patiently waiting…

WTH? Rings welded to the cylinder?