Wrong head dome nuts?

After few months i finally put the head back in place .
I checked everything maniacally before , even the studs protrusion . All went smooth.

( This thread is related to Panic reporting - valves expert opinion needed : sudden zero compression on cylinder 2, XJ6 1985 )

BUT

I used new shiny domed nuts I bought from SNG .

Only when torquing I realised that a couple of the nuts went back 1 mm or so, when I stop exerting force on the wrench . Meaning that the stud is under torsional effort which made compare the old with the new nuts

The new nuts are 3 mm shorter (!!!) so I fear that the stud is as fsr as it can go in the nut .

I cannot compare the interior deepness of new versus old nuts without untorquing the head and removing one nut …

Tomorrow I will call SNG… This is quite messy .

Question:

(1) Is it ok to untorque the head , replace nuts and torque it again , I guess it should be done in reverse order, I am sure those studs fully in the domed nut will come out with the nut.

I guess removing only one nut to check the deepness without untorquing the rest is a no go.


Rui

I don’t think removing one nut will compromise anything.

I ran into this chrome-nut problem 20+ years ago. Long story short I used double washers and all was well

I recall undoing the nuts one at a time in reverse order from the published torque sequence.

Cheers
DD

3 Likes

Short of drilling deeper and re-tapping Doug’s solution would be the way to go, unless SNG have longer nuts (unlikely if Doug had this such a long time ago)

This seems to be a common problem raised a few times in this forum.

Undo only one nut at a time and correct the problem, then refit the nut to torque. The stud will come out but it is easily refitted by double nuts.

I had the same problem and found that the threads in the nuts were not cut to the bottom of the hole. I used a bottom tap and cut all threads as far as possible, and the problem was solved.

Not original, but you will never loose sleep worrying about bottoming cheap reproduction acorn nuts. ARP stainless 12 point. No flaking chrome, will never rust.

4 Likes

They look cool, always wondered how they keep the coolant from seeping past?

Another point, weren’t all S3 nuts dull instead of chromed?

As far as I know, yes.

The chromed style is just a small amount of bling.

Cheers
DD

This is a 3.4L, so the studs are dry, but that said, even with a dome nut, if it was going to leak coolant, the faces of the nut, the chrome washer and head surface won’t be flat enough to be liquid tight.

1 Like

I simply forgot they are dry. And this very afternoon I cleaned out the blind threads on a 2.8 block. Wow.

It’s not intuitive that on the 4.2 the dome nut - washer - head seal is in fact liquid tight. I assume that the coolant could seep through the threads, hence the acorn nut, same as the cam covers.

I think it’s OK as well. My 3.8 came back from the engine builder with lifting eyes fitted - none were provided originally. So I undid two nuts at a time to remove, with no ill effects after eight years.

[quote=“RuiMeneses, post:1, topic:445059, full:true”]
After few months i finally put the head back in place .
I checked everything maniacally before , even the studs protrusion . All went smooth.

( This thread is related to Panic reporting - valves expert opinion needed : sudden zero compression on cylinder 2, XJ6 1985 )

BUT

I used new shiny domed nuts I bought from SNG .

Only when torquing I realised that a couple of the nuts went back 1 mm or so, when I stop exerting force on the wrench . Meaning that the stud is under torsional effort which made compare the old with the new nuts

The new nuts are 3 mm shorter (!!!) so I fear that the stud is as fsr as it can go in the nut .

I cannot compare the interior deepness of new versus old nuts without untorquing the head and removing one nut …

Tomorrow I will call SNG… This is quite messy .

Question:

(1) Is it ok to untorque the head , replace nuts and torque it again , I guess it should be done in reverse order, I am sure those studs fully in the domed nut will come out with the nut.

You sure cannot leave things as is, Rui - anything is better than that…

With the ‘spring- back’ you observed; the head is incorrectly torqued at that nut - and likely the others as well. The torque you read is just the twisting of the stud, of course.

It is, as others say, perfectly OK to release the nuts and retorque the head with the ‘proper’ nuts, one by one or all at once - but the torque sequence must be adhered while torquing. Unless the engine was run, there should be no damage done.

Using shims as suggested by Doug is OK as long as there are enough threads left in the ‘shallow’, nut to take the load. And Doug’s experience so indicates…:slight_smile:

While ‘gradual’ torquing was prescribed, a ‘stepped’ torquing to 1/3 or half the prescribed torque on all nuts in torque sequence - the final torque to set value must be in one sweep to avoid binding, giving misleading read.

It’s also advised, depending on torque meter used, to watch the progressive increase in torque. If at any time the torque force remains constant; you are twisting the stud/bolt - and if proceeding something will break…:slight_smile:

Adding that normal procedure is to retorquing the head after some 1500 km of driving…

Frank
xj6 85 Sov Europe (UK/NZ)

Many thanks to all.

Indeed, the best will be to remove all the nuts and put back the original ones, after measuring the deepness of the thread with a bolt to fit, and the protrusion of the stud, to make it sure .

@Frank_Andersen , the engine did not run nor I added oil or water yet so it should be ok . I’m still connecting bits and pieces, I also had to remove the bumper so that the crane’s arm could reach the block in a more central position .

Wish you all a good week ,
Rui

Indeed a good point, Rui - unless the studs are completely seated, no grunge in the block; the nuts will bottom…:slight_smile:

And a good week to you, too

Frank
xj6 85 Sov Europe UK/NZ)

1 Like

Just do them one by one following the torque sequence and all will be good!

1 Like

If it is a long stud 4.2, its very bad if the studs back out as coolant will run into the bottom threads with possible highly undesirable outcomes

pos “new” stud nuts, I had them (they are not identical to OEM externally either)

Its cheaper to rechrome originals if you have a spare set

Not necessarily, chrome in Europe is difficult as far as I know… unfortunately
Nickel would fit right in with the nice gold!

Indeed Tony, but when 3 studs came out upon disassembling I tried to pump any fluid left with a syringe and plastic pipe and blow compressed air. I did not add cooling fluid after so it should be ok, hopefully
Rui

$A5 = 2.5E each

They are only flash chromed

I have a set to be done soon

1 Like

Meanwhile I am struggling to find out what is the thread size and pitch of the studs, on the block and head sides , I recall they seem different on both ends.

I will need to order two nuts to remove the domed nuts on those studs that will come along.

It is not M10 …

SNG Holland have been completely unhepllpfull , I asked them to send me two nuts and one bolt to be able to accurately measure thread deep , both on the original domed nuts and the shorter chrome nuts they sent, but they sent 3/8 inch nuts amd bolt , definitely wrong . :roll_eyes:

Many thanks for your help

Rui

After cleaning and brushing the original nuts seem pretty decent

Work in progress

They won’t be metric in size or thread pitch. They will be Imperial in size and thread and threads per inch.