Testing to see if 4.2L engine is seized

Hi there,

I am looking at restoring a 1981 series III XJ6. It has been sitting for 15-20 years now, and before I start working on it I want to make sure it has not seized. I am having difficulty finding/getting to the crankshaft bolt to try and manually turn it over. How do I get to this bolt?

Thank you

Worth taking the plugs out , and spraying WD40 or even oil in the plug holes , may even turn by the fan belt !

You need a long flat piece of say 1/4” plate about 2.5” wide and about 18” long.weld to it a shortened socket that fits the crank damper bolt. You need a shortened socket so it clears the rad/fa. I’ve forgotten the socket size! But sure someone on here can advise.take spark plugs out, make sure it’s not in gear!
A simpler way if it’s got a battery on it, is to take the spark plugs out and see if it turns.

33mm or ¾ whitworth or the corresponding size 1 5/16?. Plugs out, oil in and cross your fingers. Fan belt not too likely as in my case it almost slips and it is very hard to get the engine moving by hand.

1 5/16" is the socket size.

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The nit-picker in me says, it’s actually 3/4" Whitworth. (BSF)

But 1 5/16" UNF is close enough!


Thats the thread not the bolt head size.

Yes, that’s what I meant. The Whitworth sizes are thread sizes but the tools are given their “names” or sizes that way. So a Whitworth 3/4" spanner or “box” is the perfect fit for the crank bolt on both XK and Jaguar pushrod engines. :slight_smile:

1 5/16" fits perfectly… just did it yesterday.

Nit away…:wink:

Somewhere, I think I actually have a wrench–er, excuse me, spanner–that size…:wink:

Yes, 1-5/16" socket.
The thread is 3/4-16 UNF as is the rest of the XK engine except a few UNC where it is threaded into aluminum, and SU carbs if you have them are BSPP.
If you can’t get in there with the socket, you may be able to find a place in the bell housing where you can get a pry bar in there and pry it on the starter ring gear.
What country are you in?

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Third vote for 1-5/16" socket. The crank bolt is very definitely 3/4"-16 UNF.

If you remove the spark plugs, you might get lucky and be able turn the engine by the alternator pulley, which is a lot easier to get to.

Why not try compressed air into a plug hole?

Rarely will that work, even on an unseized engine. Mechanically trying is the better option.

a 33mm x 1/2" drive socket from below will usually get on it

1-5/16" is typically 3/4" drive and bigger, so not enough clearance

I have a cranked 3/4 Whitworth ring spanners that slips in from below right onto the nut and near flush to the pulleys, its a beauty

Now I dont want to dispute my olders & betters, but if you slip a 3/4W (1.300") and a 1-5/16" (1.325") over the nut, the 1-5/16 is a bit sloppy. (both 6 point sockets), 3/4W = 33.02mm

I would say it is a 3/4 W


I know it is. :slight_smile:

But only those few of us tinkering with the pushrod Jaguars (or SS’s) have much need for all the BSF/BSW tools.


I have quite a large collection of Whitworth and other pre-war tools

said 3/4W reaching up onto the pulley of a 420G,
just me on the ground, car not lifted

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Yep, I can turn my '72 4.2L this way. Expediency at the expense of sore hands. Paul.

Me too. Just because a 1-5/16" or 33mm socket/spanner/wrench fit doesn’t mean that is what it is. It’s just that they both are close enough to the real size 1.300" 3/4" Whitworth. And if you take the time to measure the thread angle you will find it is 55 degrees (Whitworth) not 60 degrees (UNF). I have a 3/4" Whitworth socket (1.300") which is a nice tight fit, a 33mm socket (1.2992") that is indistinguishable from the Whitworth, and a 1-5/16" (1.3125") which is quite sloppy. All work of course, but only the Whitworth feels just RIGHT :smiley: