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  • How to Remove Broken Exhaust Manifold Bolts: Drilling vs Welding

How to Remove Broken Exhaust Manifold Bolts: Drilling vs Welding

How do you remove a broken exhaust manifold bolt from an aluminum head?

Christian Hazel
Mar 9, 2020

If you use a gasoline-powered V-8 pickup or SUV to tow a trailer, chances are you're going to eventually have an exhaust leak caused by broken manifold bolts or studs. We have a 2004 Dodge Durango with the aluminum-head 5.7L Hemi that we purchased brand new. In addition to regular commuting duties we frequently use the little workhorse SUV to tow a 6,500-pound wakeboard boat or a Jeep/trailer combo of similar weight. The passenger and driver exhaust manifold bolts let go at roughly 70,000 miles and we had them replaced by the dealership under warranty. Then, at about 188,000 miles the driver-side exhaust studs snapped. We got really lucky and those particular studs snapped off with about 1-inch of exposed stud shaft sticking out of the cylinder head. Furthermore, the broken studs were only in finger-tight, so we were able to just spin them out and replace the gasket and bolts with little drama. Most recently at 262,000 miles the passenger side started the telltale "tick, tick tick" when the engine was cold. Once the vehicle was driven a short distance, the manifolds swelled up and the tick was mitigated, but we figured we'd highlight the fix before it got too severe.

Why You Should Fix an Exhaust Leak

Under extreme use like towing heavy loads, the exhaust manifolds can go from normal operating temperature to cherry red in a matter of seconds. That rapid heat causes the exhaust manifold material to expand, which puts a tremendous strain on the bolts and/or studs holding the manifolds to the cylinder heads. After hundreds of expansion and contraction cycles, the studs or bolts finally fail. It's not too dissimilar from bending a paper clip back and forth. Eventually it's gonna come apart in your hands. With only part of the manifold cinched tightly to the engine cylinder head, the exhaust gasket will blow out, not only allowing exhaust gases to escape, but possibly allowing air to enter the exhaust stream, throwing off the O2 sensor's readings. If the O2 sensor thinks the engine is running leaner than it should, it will trigger more fuel to be dumped into the engine, potentially causing harm to the catalytic converter(s). Also, the exhaust manifolds can expand and contract unevenly, which could cause the cast iron to crack, compounding the incorrect O2 sensor readings, not to mention making the annoying exhaust leak sound worse.

Getting Access to the Engine

Every vehicle is different, but on this Dodge Durango it's easiest to gain access to the exhaust manifolds by jacking up the vehicle, removing the front tire, and then taking out the inner fender liner. We put a jackstand securely under the framerail and then got to work. Once we had access to the manifold we soaked the bolts with penetrating oil to help them come out without snapping. If you live in an area that uses road salt or you experience a lot of rain, snow, or ocean spray, you'll probably want to devote a couple days to soaking the bolts repeatedly with penetrating lube. This vehicle has been in SoCal its entire life so we just let them soak for a couple hours before proceeding.

Photo 2/21   |   Remove the wheel and tire and then the inner fender liner to gain access to the exhaust manifolds.
Photo 3/21   |   Inspect the bolts and exhaust system for obvious damage before proceeding. If you need more parts, it's best to order before you tear your vehicle down.
Photo 4/21   |   Our manifold collectors use captured nuts that had rusted apart.
Photo 5/21   |   Use a quality penetrating spray to soak all of the exhaust bolts before you try to remove them. It will help prevent further snapping and more work.

Removing the Manifold

In our case, the Hemi exhaust manifolds use four studs and five bolts. The studs hold the heat shield in place. All of our bolts came out in one piece, but two of our studs had snapped. Furthermore, two of the nuts that held the heat shield on had seized to the studs and wouldn't spin. Normally, you can't just spin the studs out with the heat shield in place, but in our case one of the seized stud nuts was on one of the snapped studs and the other loosened just enough before refusing to budge that it created enough slack to allow the stud to spin out without destroying the heat shield. We were able to pull the heat shield free and then remove the studs on the ground without hurting anything. All of the exhaust manifold bolts came out without issue, but the collector nuts that had rotted away were a problem. Miraculously, we were able to get a pair of vise-grip pliers on the nut and hold it tight enough to remove the manifold collector bolts. With all the bolts removed, the manifold and gasket were removed, exposing the broken studs in the cylinder head.

Photo 6/21   |   The snapped stud (foreground) obviously pulled right out of the manifold. The rear stud spun out after we managed to loosen the heat shield, retaining nut enough to allow it to spin on the heat shield.
Photo 7/21   |   With the heat shield removed we took all but one manifold bolt out before tackling the collector-to-downpipe bolts.
Photo 8/21   |   The collector bolt originally featured a captured nut that wouldn't spin, but the material had rotted away. Thankfully we were able to get a pair of regular vise-grip pliers on the outer nut. A pair of needle-nose vise-grip pliers fit between the collector and engine block on the inside bolt. We used regular nuts when reassembling.

Extracting a Broken Bolt from Cylinder Head

Depending on where the stud or nut breaks determines how lucky you are. Ideally, the stud or bolt will break with a bunch of shaft exposed that you can get a set of pliers on to spin it free. If not and it's broken off flush, we've had success in some cases of carefully using a sharp punch or chisel to carefully spin the stud out. However, chances are the bolt or stud will either be snapped off deep in the threads or will be seized and won't want to come out. In those cases you have two options: drill it out or weld a nut onto the broken portion and spin it out.

Photo 9/21   |   This stud had snapped off about inch below the surface of the cylinder head and wouldn't spin with a sharp punch.

Drilling can be a dangerous and unsuccessful endeavor. The idea is you start drilling in the direct center of the bolt and then step up the drill size in increasingly larger increments until you're almost at the threads. Then, you can use an extractor to spin the remaining bolt out. We've done this in the past, but it's nerve-racking because if you break off a drill bit or hardened extractor inside the head there's virtually no getting it out. We contemplated drilling our stud out, but the fact that we have aluminum cylinder heads and this vehicle had a control arm smack in the way of the drill, we opted for the welding route.

Photo 10/21   |   Even with a tight 90-degree drill, an upper control arm prevented us from getting a clean angle with the drill extractor on the broken stud.

Your other option when all else fails is welding a nut onto the end of the broken bolt or stud and spinning it out. Not only will the welding give you a secure purchase with which to wrench or spin the broken shank out, but the heat from the welding will help loosen any rust, antiseize, or other material that's helping prevent the broken shank from coming out. If you're working with iron cylinder heads you need to be extremely careful to avoid actually welding the nut to the cylinder head or damaging the threads. For this reason, it's usually best to use a TIG welder. TIG welding is much more precise than MIG welding, but not everybody can do or has a TIG welding setup. Worst case scenario there is you're removing your cylinder heads and taking them to a machine shop to have the stud extracted. However, most modern engines like the 5.7L Hemi we're dealing with have aluminum cylinder heads. With standard MIG or TIG welding, the steel welding wire won't stick to or even damage the aluminum of the cylinder head, allowing you relative safety while attempting to weld on a nut. We used a pair of needle nose pliers to hold a 3/8-inch nut over the hole containing our broken stud. Because the shank was roughly inch down in the hole, we used a relatively high wire speed to help fill the gap and let 'er rip. With a nut securely welded to the broken stud, the remaining portion spun right out with no damage.

Photo 11/21   |   We attached our welding ground to the engine and used needle nose pliers to hold a 3/8-inch nut against the head over the hold containing the broken stud shank.
Photo 12/21   |   With a relatively high wire speed, we welded the nut onto the broken shank and spun it out of the head.
Photo 13/21   |   You can see the gap between the portion of the broken stud and the nut.
Photo 14/21   |   Using a relatively low welding heat, the aluminum of the cylinder head remains completely undamaged form the welding procedure.

New Exhaust Gaskets and Studs and Reassembly

Thankfully, after a careful inspection we found no cracks in our factory exhaust manifold. You don't want to cheap out and get inferior parts when it's time to reassemble. For our 2004 Hemi we went with a factory Mopar exhaust manifold gasket and a set of new FelPro studs that we purchased from Summit Racing. The FelPro studs came with a blue coating for corrosion resistance and included thread locker on the threads. It seems the gasket design has changed over time, so after verifying the port sizes on the gasket were the same as the original, we applied some antiseize to the bolt threads and got ready to reinstall the manifold. Two of the manifold bolt holes are notched to allow the manifold to slide on. This allows you to keep the manifold gasket on the head while you manipulate the heavy manifold into place. In our case, we had enough access where this wasn't really an issue, so we assembled both gasket and manifold together, making sure to put studs in the correct holes to accept the heat shield. After getting the bolts finger-tight we broke out the torque wrench and over three passes torqued the manifold bolts and studs in the correct pattern (we found ours online) to the correct 18-lb-ft value for our engine. After the manifold was torqued to the head, we installed some new Grade 8 bolts, lock washers, and nuts and tightened down the downtube collectors to the manifold. After a test fire to verify there were no leaks we buttoned up the inner liner, reinstalled the wheel, and enjoyed the relative sound of silence when firing this engine up when cold.

Photo 15/21   |   We cleaned and wiped the gasket surfaces of both the cylinder head and exhaust manifold to ensure a leak-free seal.
Photo 16/21   |   A factory Mopar gasket and FelPro hardware kit from Summit Racing were the only parts we needed. Grand total for this job came in at $75.39.
Photo 17/21   |   The FelPro hardware kit is $30.99 through Summit Racing, but its high quality with a corrosion-resistant coating fits perfectly.
Photo 18/21   |   We threaded one bolt through the gasket into the head to hold the gasket in place while we got the manifold ready.
Photo 19/21   |   Make sure the bolt hole you use corresponds with the slotted hole in the manifold so you can just slide it into place.
Photo 20/21   |   We torqued the exhaust bolts to 18 lb-ft per the manufacturer's pattern, which we found through an online service manual. If you can't find yours, just start in the center and alternate crisscross—bottom, top, side, side—until you've done all of them.
Photo 21/21   |   With the heat shield and new collector-to-manifold bolts installed this job is a wrap.

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