What steel for cylinder head stud

[Ian HewsonParticipant @ianhewson99641]

hi

I have a problem with a cylinder head stud stripping the hole in the block of my mgb.

To repair it I am going to tap out from 3/8bsw to 7/16 bsw in the block and fit a new stud screwed 7/16 bsw at one end to fit the block and turned down to the original 3/8 for the rest to preserve stretch values.

What steel would you suggest for the stud, silver, stainles or mild?

[Ian HewsonParticipant @ianhewson99641]

[Nick WheelerParticipant @nickwheeler]

Wouldn't a Helicoil or similar repair back to the original thread size be a simpler, easier more effective job? Then all you would need is a new, standard stud

[Keith LongParticipant @keithlong89920]

Cylinder head stub on B series, most likely 8.8 or even 12.9 grade ht steel – they have a serious job to do and they get hot. The helicoil or other thread insert is the way to go. If you really want to make a stud with an oversized end then 7/16s isn't big enough. The 3/8 bsw is 16 tpi and 7/16 14 tpi, so you'll need to get rid of all the 3/8 thread. The tapping drill for 7/16 is smaller than the resulting hole in the block so you need to be looking at least one size up on 7/16 anyway.

Edited By Keith Long on 09/04/2016 14:54:42

[Ian HewsonParticipant @ianhewson99641]

Hi Keith

yes you are correct, depth of engagement would be too shallow, going to go the helicoil route.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Nicholas Wheeler 1 on 09/04/2016 14:39:17:

Wouldn't a Helicoil or similar repair back to the original thread size be a simpler, easier more effective job? Then all you would need is a new, standard stud

.

+1 for that ^^^

MichaelG.

[Keith LongParticipant @keithlong89920]

Ian – it would be worth checking the thread form on one of the other head studs to verify that it is BSW and not UNC (or even possibly metric). BMC and later BL used a right concoction of threads in their engines and you can't always judge by the spanner sizes, I believe that there are some fittings with metric threads and imperial a/f heads and nuts. As the MGB engine is (assuming 4 cyl not 8) just another version of the B series it would be well worth making sure.

I used to have a sports car which used a Riley 1.5 engine, so I've been up to the elbows in the oily bits of a B series more than once!

[frank brownParticipant @frankbrown22225]

I have read that because of the stress on head studs they are forged.. Single pointing or dieing a thread will lead to stress concentration and early failure. On many vehicle it is mandatory to chuck out the old studs and only refit new ones, because the old studs will have been stretched.

Frank

[duncan webster 1Participant @duncanwebster1]

All round bar is forged, that's how they make it (rolling is a type of forging). Bright bar is then cold drawn, which puts all sorts of stress into it, and actually gives it a higher yield stress. However, when it comes to highly stressed studs and bolts, the threads are often rolled, which gives a stronger thread than cutting, as well as being cheaper.

Helicoil is definately your answer, not only does it avoid the making of a stepped stud, the female thread is actually stronger than the orignal. Many years ago I worked on gas turbines, and all female thraeds were helicoiled from new for exactly this reason. Highly stressed bolts were changed every time they were removed, after nearly 40 years I've just about run out of the ones I 'recovered' from the scrap bin.

[steveteeParticipant @stevetee]

Not wishing to stick my oar in where it isn't wanted, but over the years I have stripped down a number of B series engines 1500/1622 and 1800. I can confirm that the threads used are all unified , so 3/8 unc in the block and 3/8 unf at the cylinder head nut end.

Surely a helicoil repair is the most suitable means of repair and then replace with a standard cylinder head stud.

There are basically 2 types of head bolts. Those which are tightened to about 50 ft/lb which then require re-torquing after 500 miles (the MGB is in this group) Most more recent stuff is tightened to about 50 ft/lb and then some thing like another 270^ of angular tightening , which I can tell you is jolly tight. These type do not require retightening , but the bolts are replaced each time the head is off, as they have stretched during initial tightening.

Series 3 Landrover used a bizzare mix of Metric and Unifed, but thebolts on the gearbox for the prop were BSF

Edited By stevetee on 10/04/2016 01:28:51

[Neil WyattModerator @neilwyatt]

Perhaps most useful to you is an economical source of helicoil sets. Try Tracy Tools:

http://www.tracytools.com/helicoil-thread-repair-kits

3/8 UNC is £32, but with 15 inserts that's a little of £2 per stud.

http://www.tracytools.com/helicoil-thread-repair-kits/unc-thread-repair-kits/3-8-x-16-unc-thread-repair-kit

Neil

[Ian HewsonParticipant @ianhewson99641]

Hi All

Thanks for the advice, gratefully accepted.

Having re checked the threads size it is indeed 38 unc not bsw as I had thought, my eyes are getting older lol.

I have ordered a helicoil type kit and will pull the head next weekend, back permitting, my mind still thinks I am 20 but my body reasures me I am 72!

Edited By Ian Hewson on 10/04/2016 10:30:51

[Ady1Participant @ady1]

Cylinder head stub on B series, most likely 8.8 or even 12.9 grade ht steel

I cut down an do stuff with small ht hex bolts quite regularly and they usually need carbide to work them because they are so tuff

[korbyParticipant @korby]

Had an MGB a long time ago rust and mech failures ment I spent more time fixing it than driving.

I am sure the threads were UNC and UNF not Whitworth.

One thing with the studs was that heat and stress could cause a raised bit around the studs in the block , I know cast iron is not supposed to stretch but it did happen.

Dealers had a tubular running down cutter that fitted over studs to remove the bulge other wise the head would bottom on before the head gasket was fully compressed.

An easy way in the home workshop is a big countersink on the lower surface of the head stud holes.

This avoids metal to metal contact. There is not a great amount of iron around the tapped stud holes so helicoil needs to be done by an expert. I had the thermostat fail and boiled up the engine cracked the head common problem on MGB cost me a new head

Best of luck with your rebuild.

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