Exhaust Manifold Gaskets and Snapped Stud

I’ve had trouble with the front exhaust manifold gasket on my 1990 4L XJ40 blowing because it’s missing a stud. Actually the stud was snapped off level with the side of the engine block, the outer part stuck in the manifold, possibly since before I bought the car. It’s the rear-most stud for the front manifold, as can be seen in this photo.

That photo was taken last time I replaced the gaskets, when I also got the rear manifold resurfaced and attempted to extract the broken stud. After spending the bulk of two days drilling progressively larger holes into it then snapping off progressively bigger easy-outs, I gave up.

That gasket lasted almost three years, but now it’s leaking badly again so I set about replacing the front gasket, only to discover that the rear manifold is now missing a stud as well!

I guess I caused so much shock and vibration working on the remains of its neighbour that this other one losened up and wobbled out later while driving. But I seem able to thread a stud in OK for that one. I just need a new rear gasket now since I only have a front one, but while shopping for them I noticed something…

The genuine Jaguar gaskets look quite different to the aftermarket ones I’ve been using (as seen in my first photo):

Which is better in my case? The Jaguar ones look like solid metal, so they might be stronger, but perhaps they wouldn’t seal as well as the more ‘spongy’ aftermarket ones place without the stud on the front manifold? I’ve only ever seen the aftermarket ones in person, so suggestions welcome!

Plus of course, any ideas about actually getting the snapped-off front manifold stud out? I’m done with easy-outs, I can’t drill a bigger hole that’s centered accurately enough that I wouldn’t hit the threads (and I’m not sure there’s enough stud left to turn anyway). But that gives me another idea: could I try tapping a new M10 thread into the combined remains of the old stud and the old thread? I’ve never tapped a thread in a hole before, but it’s the only idea I’ve come up with in three years.

That kind of a nightmare is where I would call in the professionals but that might require removal of the head and taking it to a competent machine shop. I think they have ways of lazering out broken studs. At least I recall from my Jaguar warranty days that they could do that for the 4.2 XK engine head studs that went down inside the water jacket and tended to snap off if they got rusty.

That is a nightmare kind of job but with a LOT of patience you might still be able to complete it without removing the head. In your position I would buy a strip of 1/2" thick flat bar, wide enough to completely cover the area where the manifold sits. Use the manifold as a template to accurately mark the positions of the studs and drill the holes to the EXACT size of the studs in the flat bar. Make two of them so you have about 1" total thickness. Use the good existing studs to fasten the flat bars to the head. Use the hole where the broken stud is as a guide to keep the drill bit perfectly straight. That’s why you need about 1" depth, it will keep the drill bit straight. I don’t know what diameter the studs are so I can’t advise a drill size, however if you measure them with a vernier caliper or can find out the correct thread size of the studs there are charts available on line to inform you of the correct size drill to suit the tap you will need. It will probably leave a thin sliver of the old stud in the original threads but the tap will remove that.

I’d just bolt up the manifold with the other two good studs then using the bad stud manifold hole as a guide, drill out the old stud. If necessary re-tap the head or worst case scenario use a helicoil in the newly drilled hole.

Thanks for the suggestions. I think the professionals will be out of my price range, but one method I’ve come across which they might have used was EDM. The machines like these can be quite small, but the metal being worked on needs to be submerged in liquid so that would require removing the head.

Casso’s idea sounds good. I don’t think the manifold hole is thick enough to keep the drill straight in the awkward position that I have to hold it, but that might be a good way to get the hole in the bar stock in the right position. I could drill the mounting holes for the bar, then fit the manifold over it on the engine block and drill in a little through the broken stud’s hole to mark the correct centre position. I might have to use a thinner piece for that and then use it as a template to drill the thicker bar stock. Conveniently I’ve already got a good selection of steel bar to work with. It’ll keep me busy.

Stud size is 10mm, regular thread. I’ll buy a suitable tap today. Hopefully it doesn’t end up snapped off in there like all the easy-outs did (drilling them out was half the battle last time).

Worst case if I make a complete mess I’ll just have to keep replacing the gasket about every three years (or longer with the Jaguar gaskets, if they are stronger?).

Are you using left-hand twist drills to drill studs out?

Using regular right-hand twist drills will, if anything moves, just make the broken off piece tighter in its threads.

Left-hand twist drills have the advantage of also trying to back the stud out as you drill, and sometimes that is enough to break the broken stud loose from it threads.

Also heat the stud with a torch, then let it cool back down. Heating the broken stud expands it, yes, making it tighter, but in expanding, the stud may break rust, crud, whatever, loose enough for the left-hand twist drill to back it out.

Another option is you are good at welding and can access that area, hold a nut in place over the broken stud and weld in the center of the nut to the stud, you now have a larger nut to wrench the stud out with, maybe even use one of the impact type cordless screw guns with an adapter as a small impact wrench on it.

Just meandering through my mind of things I’ve tried and learned about doing, some from posts here.

Actually I only found out about those left handed drills yesterday, and thought regular drills were my only option last time. After my earlier attempt there’s not enough left to weld to, and I think it gets as hot as I could make it regularly there anyway. After all my attempts with ever bigger easy-outs it looks like I’ve just drilled a new hole in the block where there never was one before.

But yes it might be a good idea to try getting a left-hand drill for this attempt.

A left-hand twist drill bit with the drill in reverse ‘can’ do wonders … hopefully it works for you.

Here’s an idea that might break whatever it is stuck with loose: put a piece of steel rod (an old screw driver with the blade and handle cut off would work) in a hammer drill and use the hammer setting to repeatedly hammer on the broken stud. That force and vibration may break the thread loose.

That can’t hurt anything (other than your hands, maybe), and it might help.

Then drill reverse with left-hand twist drill.

Maybe even alternate between the two.

I have done 5 of these extractions in-situ over the last few years with 100% success on my daily driver Saabs. Alloy head, steel studs. I made a guide out of a bolt that was a sliding fit inside the manifold hole, with no slop, cut to about 25mm long, and centre drilled in a drill press with the same drill size as I was using for drilling the stud remnant. I used a reverse drill bit and was careful not to drill too deep. In every case an easy out sized for the drill bit size was easily able to remove the left overs. Access constraints also meant I had to use a right angle gearbox on a portable drill to fit in the available space. From memory I used a 3.5mm reverse drill bit, and studs had 13mm AF nuts, so M8 I think? Easyout size to match drill size. Don’t skimp on quality!
Cheers, Dave

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Mr. OmberJag …

So it’s the rear stud on the FRONT manifold that’s sheared off and the front stud on the REAR manifold that’s just missing. Right ?

Well replacing a missing stud (it’s really hard to believe that thing could have just worked it’s way out) is no problem.

If you’re trying to remove a sheared exhaust manifold stud it’s already telling you it’s basically welded itself in place. You can spend hours and hours trying to drill a stud out only to have the easy out snap off. Ask us all how we know.

If the stud is sheared off flush or above the head save yourself all the headaches and simply have a bolt welded onto the end of the stud, This almost always works because of two things …

  1. The weld builds up to the full diameter of the stud giving it much more strength when unbolting it.

  2. The super high heat generated by welding will also go a long way to breaking down the corrosive bond that’s formed between the head and the stud.

Before you start try working out a deal with a mobile welder for 10 minutes of their time or get a strap and tow your car over to a shop.

I’d consider pulling the head as the very last resort !!

Yes the rear manifold stud is gone somehow, all I know is that I’ve got photographic proof it was there before, and I poked a nail in to check there wasn’t any snapped off in the hole.

By the end of my first attempts to remove the snapped front stud in 2021 using easy-outs there wasn’t any clear stud end left to weld onto anymore, but I’ll note that method for next time. I’ll go with drill and tap, but using left hand drills just in case it encourages some of the stud to come out. I’ve got the other stud hole now to tell how deep I can go.

I guess I’ll order another aftermarket exhaust manifold gasket since nobody is singing the praises of the genuine ones. I know the missing studs are the reason they’re blowing, my interest is mainly in case I have to give up on that front manifold stud and make do without it again (I’ve managed like that for ten years now, so it’s not the end of the world).

In the case you are in, I would do one of two things

  1. drill and tap to the next size up, be it metric or imperial, screw a stud in using 2 locked nuts

  2. drill and helicoil it (there are other products)

This is a good quality repair, the kit cost is maybe $50-100, but what is your time & annoyance worth ?

I have done both, and every other method suggested. If the stud is broken flush, a washer can be placed over the hole, with a nut, and mig weld it

Yes I might go with the helicoil approach actually. Since I’m not sure how much I might have accidentally drilled into the threads before while trying to remove stuck easy-outs, drilling all that mess out might be the cleanest solution. I’ve ordered a kit from Ebay (also an aftermarket rear gasket).

As usual I intended to spend the weekend fixing something on the Jag, and instead spent the weekend researching/buying things to use to fix the Jag next weekend. But at least I’m learning a lot!

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Great idea!

While that gives you a good ‘center of the exhaust manifold mounting hole’ spacer for the left-hand twist drill bit, we all know that those holes are not always exactly over center of the bolts, leaving a slight bit of slop/adjustment/wiggle of the exhaust manifold around its bolts … but it should get the drilled hole quite close to stud center and provide a no-drill-wiggle guide.

I’ll have to mentally add that to my list of ways to remove a broken stud.

Yep, mine were all slightly off centre in one or other direction, but drill size meant there was still a decent margin. Mind you, Swedish steel rather than English, so probably less prone to rust in place :smirk:

I finally finished this job off last week after delays waiting for tools and bearable weather.

It turns out I’d confused myself with the first photo and it was actually the rear exhaust manifold stud that was snapped all along, the photo was older than I thought and it must have happened later. I’d drilled out so much of it that the wire I poked in went the full depth. The other stud has been coming out because the nut was siezed, I’ve replaced that stud now too.

The helicoil thread replacement went well except that I needed to cut the kit’s drill bit way down to fit in the space, even using a right-angle drill attachment. Then my cheap right-angle attachment broke and I had to get a better one (though there don’t seem to be really good ones available anywhere) which worked. I also used an 8mm end-mill bit to drill out most of the old stud first, it being short enough to fit without cutting it down. A length of 3/4" steel bar mounted to studs either side served very well as a guide for drilling and tapping, thanks for that tip!

One thing to note is that residue from the cutting lubricant I squirted liberally for tapping the thread made lots of smoke in the engine bay when the exhaust first warmed up, and it took me a while to figure out what it was coming from while I kept an eye on the nearest fire extinguisher.

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If you have any future problems with the exhaust manifold, next time you remove it say for replacing gaskets, check the flatness of the removed exhaust manifolds with good metal machinist ruler or drill rod. You might find they are not flat anymore obviously a machine shop could machine or grind them flat or on mine I sanded them flatter with sandpaper on thick plate glass. Machine shop would be best but sanding can certainly flatten the mating surface. Good thing to check next time they are off.