The 'E' Type Forum

Hi all anyone know of the top of their head the tourque setting s for spark plugs in jaguar xk engine . A mate asked me today and I said I'll find out ..... mine are done up to the click in my elbow ... but this guy is pedantic about these sort of thing . Cheers for any ideas

I do not torque spark plugs. Not ever.

All new plugs are fitted with crushable washers (except those with taper seats, which our XK engines don't have). I follow the instruction to do them up. A torque wrench is never used.

I know that aluminium crystallises when worked, i.e. when threads are repeatedly torqued. This is why threads strip. I've had one plug thread strip already, so every time I replace the plugs I am very careful when winding them to crush the washer.

Absolutely as Chris Fell said. No torque setting. The proper technique is to make sure all threads are clean, and then tighten the plug onto its seat by hand as far as possible. When home, use a plug spanner to tighten a further one-eighth of a turn

There is this from NGK:
http://www.ngkntk.co.uk/index.php/techn ... ng-torque/

Agree with Chris not to go too tight and the NGK shows less torque for aluminium heads, why not aim for the lower setting and get a feel for how tight that seems?

Geoff

Hand tight then a nip with a socket. Never torque...

Plus, I always apply a light coating of antiseize to the threads. It helps to prevent dissimilar metal corrosion.

cactusman wrote:Hand tight then a nip with a socket. Never torque...

Aren't "Hand tight then nip with a socket" and Christopher's 'hand tight then a further eighth of a turn' themselves both (loose) expressions of torque?

(Genuine question from someone who's never used a torque wrench except on a bicycle where they are routinely used at low torque settings to prevent over-tightening which might otherwise cause alloy threads to get stripped out or expensive carbon bits to get crushed)

Simon : not really ( except in the most literal sense) . They would be if there were not a crush factor involved on the plug gasket . If you look at a new plug and compare it with a used one , it will be seen that the new one is bulbous whereas the used one has been flattened .

I must say that I'm surprised that the consensus so far is not to use a specified torque. That goes against every engineering good practice.

I use a figure of 25 to 30 Nm when I fit plugs (14mm thread) in aluminium heads. This figure is for dry assembly. I don't lubricate because plugs are pulled and cleaned regularly. If you must lubricate, use around 16Nm.

This is the only way you can be sure that the plug is both properly seated and not over-stressed.

The sealing washer collapses when first used so using a controlled torque ensures the plug seating is consistent.

Regards

Hmmm... More confused than ever now! I think I'll recognise my limitations and stick to fixing my bicycle - although they do say that if you can fix a bicycle you can fix a Type 42 destroyer!

Simon, you fixing a Type 42 destroyer? God help the Royal Navy

An observation. I torqued my plugs to the low figure for aluminium when fitting an overhauled head on my engine a few months ago. With all the comments about NOT using a torque wrench I today checked all the plugs and they came out readily.

Having seen some brutes who don't appreciate just how much they do up nuts/bolts etc. then it is a useful exercise to use a torque wrench just to appreciate how low some of the settings are.

Just my thoughts for what they are worth

Geoff

Au contraire. I'd be quite a handy person for the Royal Navy to have if ever they wanted their Type 42 destroyer washed, polished and detailed...

Simon P wrote:Au contraire. I'd be quite a handy person for the Royal Navy to have if ever they wanted their Type 42 destroyer washed, polished and detailed...

There's a job for life, especially if you do interiors too.....

The Jaguar Service Manual states:

Tighten the sparking plugs to a torque of 27 lb.ft. (3.73 kgm). [Service 02 Engine Page B.55]


That converts to 36.6 Nm

Thanks, Mark

I thought it would be somewhere in the manuals.

That setting sounds high although I suspect it's well within the thread's stress tolerance range. It depends largely on the type of thread insert fitted in the head.

It's unfortunate that the basic design of spark plugs doesn't give us the opportunity to install them without the risk of stripping threads.


Still, it keeps us on our toes.

Regards

mark10337 wrote:The Jaguar Service Manual states:

Tighten the sparking plugs to a torque of 27 lb.ft. (3.73 kgm). [Service 02 Engine Page B.55]


That converts to 36.6 Nm

You follow that advice if you want to. I will ignore this for the reasons I've already stated, not the least of which was that Jaguar's advice was for a brand new engine, not a fifty year old engine.

Of course YMMV, and any lister is free to take whatever advice they choose. What I do is based on experience.

There is one other factor which so far we have not considered, and that is temperature. In my youth, we were told never to remove or replace plugs in an al2 head when the engine was hot. Presumably because, as the head cools, whatever torque has been applied effectively is increased as the thread pitch contracts as the head cools

Ok Chris

Following your logic then I assume that you don't torque cylinder head bolts either?

The whole point of torque control is to keep the materials used within their safe working range. If you do that then it doesn't matter whether the engine is new or fifty years old.

Regards

So how about removeing them.....im sure we have all had this problem at sometime.......not too long ago i posted here becaus my plugs were stuck fast, and would not move.....it was me that put them in useing the hand tight then just nip up.....tried all the usual penetrating oil, acetone and atf.....nothing would work....so next was if im going to have to pull harder is it best when the engins hot or cold......I went for hot......fortunatly they all come out but was expecting a stripped thread......they took quite a bit to undo.. Steve

I have yet to meet a garage man that torques spark plugs. So long as they are tight enough for the crushable washer to seal then they are tight enough. Aluminium does work harden and as all our heads are way past Jaguars intended service life it is, in my view, folly to tighten them any more than is absolutely necessary to obtain a good gas seal. Things that require torquing up are usually not routinely undone again. Indeed some high torque bolts should be replaced after use e.g. caliper bolts. Torque is applied for good engineering reasons and in cars is usually present where failure of the joint would be either catastrophic (brakes, steering and suspension), or very inconvenient (engine internals and the like).but it not always needed. One would not routinely torque up a trim bolt. Spark plugs are service items that are routinely removed for maintenance or replacement and repeated torque applied to the aluminium threads will eventually cause failure I would guess although how long this might take I don't know. I will continue to use a dab of copper ease, hand tighten and then nip down as is common practice among many a garage mechanic.