Studs or Bolts ?

[Royston W]

Exhaust manifold GT6 mk3 is missing some fixings ! 

anyone know what they are please, bolts or studs, and size too would be good.

thanks in advance if you can advise.

cheers

Royston

[johny]

How strange - I hope there not snapped off in there or the thread stripped😮

[Royston W]

I've poked a wire down the hole and I think they are just missing !

 

[Royston W]

I presume all bolts on the Triumph are UNF thread ?

 

[Colin Lindsay]

I'm trying to remember if those are just rollpins or dowels not bolts. I think they might be?

[Royston W]

Sorry , but while I'm attempting to understand Bolt dimensions, could I also ask about spanner sizes too, does a 9/16" spanner relate to a 9/16" bolt ?

The bolts on the end of the exhaust manifold are definitely undone with a 9/16" spanner , and their thread seems to be UNF,  

[Pete Lewis]

these exhaust fixings are studs and nuts  being   3/8unf x24 on your Mk2 6cyl  ( 9/16AF spanner )

as for spanner sizes  1/2 af is the width across the hex flats and would be 5/16 x 24 UNF 

9/16AF  is for a 3/8 x 24 unf nut/bolt 

MkII 2 Litre Cylinder Head : Canley Classics

MkII 2 Litre Manifolds : Canley Classics

[Josef]

13 minutes ago, Royston W said:

Sorry , but while I'm attempting to understand Bolt dimensions, could I also ask about spanner sizes too, does a 9/16" spanner relate to a 9/16" bolt ?

The bolts on the end of the exhaust manifold are definitely undone with a 9/16" spanner , and their thread seems to be UNF,  

UNF spanner sizes are given as AF. This means ‘across flats’ - the distance between parallel faces of a nut/bolt. The thread size is the diameter of the actual threaded part of the bolt. 
 

Normally a given thread size corresponds to a given spanner size. But there are exceptions (seatbelt bolts usually have larger than ‘normal’ heads relative to their thread for example)

[Colin Lindsay]

17 minutes ago, Royston W said:

Sorry , but while I'm attempting to understand Bolt dimensions, could I also ask about spanner sizes too, does a 9/16" spanner relate to a 9/16" bolt ?

The bolts on the end of the exhaust manifold are definitely undone with a 9/16" spanner , and their thread seems to be UNF,  

See which size of spanner fits the bolt shank, not the head. That's the lazy man (me) method of checking the required size. A 1/2 inch spanner might fit the hex head but the actual hole required is 5/16, and so on, so I'll fit the bolt into a smaller spanner and if it touches the sides of the 5/16, or a 3/8 or 1/4 then that's the size I need.

[NonMember]

56 minutes ago, Josef said:

Normally a given thread size corresponds to a given spanner size. But there are exceptions

There's a particular oddball with the 7/16"UNF which is specified to have 5/8" AF bolt heads but 11/16" AF nuts, IIRC.

[Josef]

9 minutes ago, NonMember said:

There's a particular oddball with the 7/16"UNF which is specified to have 5/8" AF bolt heads but 11/16" AF nuts, IIRC.

The one I was thinking of was 7/16” UNF. I’ve got ex seatbelt fitting kit bolts with larger heads than the non-seatbelt specified ones I bought. Recently fitted a vice to my metalwork bench with a mix of these so it was stuck in my head. 

[Stratton Jimmer]

This might be useful to you Royston W:

 

[Royston W]

thank you for all the info. Seems like I will have to remove inlet and exhaust manifolds in order to gain access to the stud holes. Just to complicate matters I searched all the spares that came with car , including a large box of nut and bolts of assorted sizes and threads ( certainly not all from this car) and found 3/8" stud with UNC one end and UNC the other so if this is a missing stud ,the holes in the head might actually be UNC. 

Life is never simple.

Thanks again

Royston

[johny]

Certainly something strange seems to have happened to leave out those fixings - the exhaust gasket wont last very long before leaking. Can you take that bolt out on the far RH end of the exhaust manifold or find a suitable length 3/8 UNF bolt and try it in the empty holes to verify what the thread is and if its any good?

[Steve P]

I see the end one is a bolt,that`s what i have on mine.All UNF.

Steve

[johny]

Yes theyve got changed over the years but would have been studs originally to facilitate installing the gasket and then sliding on the whole manifold assembly. I would expect UNF in cast iron and then the courser UNC thread used in softer metals or where theres risk of cross threading...

[Royston W]

unfortunately there is no access to " the holes" without taking off carbs and inlet manifold, just ordering new studs and gaskets from Rimmer bros and have begun the tedious task of removing carbs ( fitted with heat shields that restrict access to their bolts too)

Oh the fun of it, just unbolting stuff , taking it off, putting it back on, 🤪 then tightening it up again, a mechanics life !

[Pete Lewis]

the studs are 3/8 x24unf both ends  the head is  tapped 3/8" x24 UNF   they are not UNC 

you can use a setscrew iinstead of studs  f you can get them in and aligned without removing the manifold 

you only need a length in the head of 1.5 times its diameter so thickness of flange plus around 0.6"

Pete