How to Remove a Broken Engine Bolt: Welding vs Drilling

We’re going to break down the pros and cons with each strategy, the level of experience each method requires and the average success rate with each repair method.

At ProMAXX Tool, we don’t compete with the technique used to weld onto a broken exhaust manifold mounting bolt, we actually complement it. You may find this surprising, but just like you do every day, you diagnose problems and you determine the correct approach and application of the tool or tools you have to make the most effective and efficient repair. After all, flat-rate doesn’t pay the bills, your expertise and efficiency do.
In the case of a broken exhaust manifold bolt, welding is an option, not the only option... and some technicians rely on this single approach. We all know that one approach does not fit all applications so the application is the driver for this repair. Completing the repair in minutes or hours depends on which process you use to determine the application.

We know a thing or two about broken bolts because we work with technicians every day, developing tools that will boost their productivity. Moreover, our founder has and continues to remove broken bolts in dealerships and shops around the USA. He stopped counting at his 500th removal, just over three years ago. A broken bolt is one of the most frustrating things a technician is going to experience; in fact, it’s often avoided. When a technician comes across their first broken bolt, a quick Google search will most likely suggest the two options:

Option 1: Welding on a Broken Stud

A MiG welder is the preferred tool for this job, but a stick welder, depending on where the break occurred (depending on the application: above, below or flush with the cylinder), may also do the trick. To start, select a nut or flat washer with an inner diameter roughly the size of the stuck threaded bolt. Place the flat washer and/or nut on the bolt and weld the inside of the nut to the broken top of the bolt. Then use a wrench to remove the nut and bolt together. Some technicians avoid the washer/nut combination altogether and simply “build” the weld creating a custom-fitted bolt that once above the surface of the head can be removed later. The welding process can be lengthy; the remnant needs to be cleaned in order for the weld to adhere, the temperature needs to be right in order to avoid burning the head and the steel you are welding to needs to be understood. For example, titanium alloy bolts found in most turbocharged engines take a great deal more heat to fuse to and much greater caution. Plus, getting a welding head into limited access, low-vision areas presents another set of challenges. Lastly, welding is not 100% effective in every situation. Just like other repairs, not any single solution works universally across all situations - again application.

The Pros:

- Welding is a relatively low cost and can be quick given the right application

The Cons:

- Requires a solid knowledge of welding and heat transfer

- Not 100% effective

- Can be time-consuming with equipment set up, heating & cooling and multiple attempts

- Modern engines contain a lot of dissimilar metals, which can make getting welds to stick very difficult

Experience Required:

Moderate – MiG welding, metalworking

Option 2: Drilling the Stud Out

Drilling out a broken stud or bolt can be an intimidating task for some technicians, especially if the bolt is of a smaller diameter such as the case of an exhaust manifold bolt (8MM) and a cold reminder that there is only a few thousands of an inch of cast aluminum web separating the water jacket from the manifold bolt. The traditional method includes taking a punch and creating a divot (or center point) on the broken bolt surface, drilling a pilot hole freehand, hammering in an easy out extractor, then attempting to back the bolt out. Even the greenest technician can manage this task, however, it can come with a series of things that can go wrong or create a bigger mess than when you started.

The most common issue comes from using cheap materials and off the shelf drill bits which can lead to off-center drilling. Walking drill bits and extractors can break and lengthen the repair cycle and rob your productivity and profitability. Lastly, drilling free hand and off-center introduces a torque moment at the center of the bolt which increases the energy required to remove the broken remnant, often exceeding torque specs of the extractor.

The Pros:

- It’s a much more consistent & predictable repair

- With the right tooling, it can be done by a technician with any level of experience

- When space is limited, this can be the best option before pulling the entire engine head

The Cons:

- Without the proper tooling, you can turn a difficult job into an absolute nightmare

- Using cheap drill bits and extractors will almost always lead to a botched job

Experience Required:

Low – basic drilling operation

Option 3: Specialty Tooling

Understand The Application. Use the right tool for the right application, one size does not fit all. At ProMAXX, we think these two approaches can be used together, not compete, and depending on the application, exceed expectations.
For broken bolts above the head, weld. Broken bolts flush or below the head, drill.

A specialty tool we recommend with drilling: The ProCutter - Deburring Tool

When manifold bolts are heated to high temperatures when exposed to water from the road or condensation, then can break under the slightest bit of tension. When these bolts break, it’s because they are actually stretched, thus elongating the threads. This environment often leads to a partial thread being left behind locking the stud into the softer aluminum of the head. You’ve got to go in and clean the debris, corrosion and partial thread that is left behind and this is where and why welding will fail. Introducing the ProMAXX® ProCutter™. The ProCutter™ is a unique; tool which consists of an aggressive four-blade cutting edge screwed onto an arbor and attaches to a ¼” drill, that can knock the burr of the broken remnant in just five seconds making it ready for extraction.


Remember, you are attempting to make a critical repair that requires machine shop precision and capability at the point of repair. Use the right tools, for the right application, and from the right manufacturer.

● Select the proper tooling to do the job: high quality, machine grade center point, (not split point) precision turned and ground tooling.

● Use screw-in drill bushings and precision made guide plates keep your tooling on center and perpendicular to the surface of the cylinder head.

● Be sure to use tooling that can drill through a case hardened bolt with a hardness exceeding a Rockwell “c” scale of above 35, Rc35.

● If you are going to use an extractor, avoid the left-handed tapered style. All they do is elongate the repair by deforming the broken bolt pinching it into the head. They also only turn left-handed, against the burr created when the stud broke in the first place. Choose a splined straight extractor that first, does not expand or deform the stud or bolt into the head. Second, turn it clockwise first to unlock the stud then counter-clockwise to remove it.

● Another option that we at ProMAXX trademarked – Extractorless, e.g., avoiding the extractor all together: simply drill, tap, done.

An exhaust manifold repair approach depends on the type of application; not one tool, or approach, but let the application along with your diagnostic thinking to determine the best path to a successful and efficient repair. Oh, one more tool needed to make this repair, patience. Being smart, choosing the right application and the right tools for the job you have practiced for many years in your career is the difference between flat-rate success and flat out failure.

QUESTIONS? Contact ProMaxx Today

As always, please consult with your local authorized shop before making any repair decisions. If you have any questions, feel free to call 724-302-3938 email and we will provide the expertise you need for your exhaust manifold problems!

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