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Engine stud issues


StevieH

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Just started putting engine back together after changing head gaskets. Put LH side on and tried to torque up the studs and found one would not torque, it kept turning. Removed head again and found that hole was too big for stud. On closer inspection it looks like someone has previously either rethreaded the hole or stuck what i believe is a helicoil in it, hence engine gasket going. I can just make out a small circular shaped piece of metal at the bottom of the hole.

What do I do next, do i try and get the item out,,,looks pretty well stuck or do I drill the hole out and put another helicoil in. If so can anyone tell me what size helicoil kit i need to get or at least what the thread size etc is of the stud...or am I stuffed and need a new block.

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Hello Stevie,

it's unusual for a helicoil to come out. You really need to determine if that is the case and if so what is the condition of the thread in the block. It may be possible to fit a new coil if the thread is sound.

I'm not familiar with the Stag engine, so going further oversize depends on how much metal there is? If you have to and are able to go that way probably the easiest option is to have a special stud made the the original diameter and with the base to the new thread, i.e a stepped stud.

Alec

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Cylinder Head Stud = 7/16" UNC


Strange that that has got 'buggered'!   :-/

The drill size for that Recoil/Helicoil is 29/64"     So if that hole is smaller than this you can do a recoil fairly easily.

I'd be a bit cautious re a stepped stud owing to the grief you can have getting a Stag head off. If you have a stepped stud you wont be able to remove the stud with the head in situ.

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Hello Richard,

is the Stag one of those engines you need to remove studs to lift the head?

If that's the case and the block has already been fitted with a helicoil that is now damaged then the next option to salvage the block is to tap to 9\16" or 5\8" and fit a sleeve tapped internally to 7\16" This should be pinned or preferably fitted with a small grub screw midway between the block and sleeve to prevent it turning when removing a stud.
This is always assuming sufficient metal in the block?

Alec

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piman wrote:
is the Stag one of those engines you need to remove studs to lift the head?

If the engine is in the car all the studs need to be removed in order to remove the head.  If engine is out of car then I think you can remove heads without stud removal.  Bear in mind that the foremost and rearmost studs fit slightly higher in the block - not all 5 in the same plane - but they do fit at the same angle.
In most cases, getting the studs out is a slight pain and more often they can be awful.  In such a case pulling the head over the studs isn't really possible.
piman wrote:
This is always assuming sufficient metal in the block?

Genereally there is.  Which stud is it?

Julian

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Its the stud nearest the bulkhead, the rear one. I think if I but a 7/16 unc helicoil repair kit and insert another helicoil it will stop at the top of the stuck one which will give the engine stud something to stop against and prevent the helicoil from going too deep like this one appears to have done.

Does anyone have any experience of doinfg this, I was just about to buy the7/16 helicoil repair kit from ebay when I noticed it had a /16 die in it.....surely it would have a bigger die as once the helicoil is insered I want to be left with a 7/16 hole to accept the stud? or am i confusing the issue.

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Hello Stevie,

I've used a kit called recoil which includes the correct oversized tap. I don't think you can put two coils into the same hole as you'll be very lucky to get them in phase and the fastener will stop at the bottom of the last coil fitted.
I found them very easy to use and worked well.

Alec

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On something as critical as this, where you will probably only get one chance to get it right before the block is scrap, you really need to let someone that is experienced in helicoiling engines have a look at it. and it would probably be prudent to get them to do it for you.

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Me again, I've looked at recoil kits and I'm going to give it a bash as i think the coil has simply fallen through the hole. Trouble is there are two different sizes on offer

7/16 - 14 or 7/16 - 20, this I assume is to do with coarseness of the threads, can anyone advise which is the right one for the Stag, I am guessing the coarsest at /19-14.

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Hello Stevie,

Yes that's right it's the thread pitch,  20 tpi will be UNF and 14 tpi will be UNC. Just count the threads on the stud against a rule, I would say that the head nuts will be UNF so you could compare the top of the stud with the bottom, UNC is quite noticeable against UNF,

Alec

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piman wrote:
Hello Stagnl,

UNC, are you sure, I've on ever seen UNC nuts on manifold studs? Virtually every nut is UNF?
What material is the block, aluminium or iron?

Alec


Alec, says in the Repair Operation Manual under Torque Wrench Settings:

7/16" UNC cylinder head bolts                      55 lbf ft
7/16" UNC cylinder head studs                      55 lbf ft
5/16" UNC inlet manifold attachment              20 lbf ft

Block is iron, cylinder heads and inlet manifold are aluminium.

I've had the bolts 'n' studs enough times in my hands to tell that they are indeed UNC.  Manifold attachment bolts strip their corresponding head threads very easily - it is common to see helicoils in these holes.  As for the block - I've not heard of one stripping but I guess anything is possible as this area in Stag engines can be a right pain in the rear.

Julian

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Hello Julian,

I wondered if you had made a typing error?

However tapped holes, particularly in aluminium are almost always UNC (Exception - rear hub studs on the Triumph swinging arms.), but I expected the nuts to be UNC? I.e., studs with UNC one end and UNF the other.

Alec

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  • 1 month later...

Troops

Finally got the engine back together, I can now helicoil into both iron and aluminium...you could call me the helicoil king but someone on ebay has blagged the name.

Put the engine back together including a sump removal...not an easy job.

My luck finally changed and she started first time and is running sweet as a nut.  Next job is a service on the autoboxx and then i will drive her until the winter gets here and then work on the bodywork...happy days.

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