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Releasing seized nuts and bolts



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What is the issue?
Bolts and nuts like almost every fastening, have a tendency to seize up on boats due to the challenging sea going environment.

Why address this?
We've all come across a seized screw, bolt or nut that can halt a project, cause frustration and cost money.

How to address this?
The first rule, when a stubborn seized bolt is encountered, is to stop and take stock. Getting frustrated or angry will put you at risk of making it much worse. Resist the temptation to force something that shouldn't be forced. The consequence of breaking or ruining a fixing makes patience a virtue, take your time and keep trying without using any excessive force with the right tools.

Tools for Seized Bolts

The first point of call for most people is to reach for the trusty and meaty vice grip. This should be avoided as they tend to crush the nut onto the bolt and strip off the nut or bolt's flats.

A common open ended wrench with a boxed in 12-point ratchet
Photo: Courtesy of Husky


An open-ended wrench is just as bad in this respect as it also strips off the corners of the bolt. Always turn the spanner or wrench around and use the boxed in section which is the better option.


A 6-point ring spanner
Photo: Courtesy of Gear Wrench


The most common ring spanner profile is unfortunately the 12-point, or 'bi-hex', profile, so-called because it has 12 points and troughs. But like open wrenches, the 12-point profile is shallow and more likely to slip and strip off the edges. A better option is to purchase a heavy set of 6-point wrenches for this type of task. In most cases, a 6-point socket (hex) will grip a rusted nut better, with less possibility of damage than a twelve point socket (bi hex) or conventional ring end spanner.


A hinged ½ inch drive breaker bar
Photo: Courtesy of Heamar


Avoid ratchet spanners or sockets of all types to free heavily seized bolts as they can break under the load. Use instead a fixed breaker bar specifically designed for loosening tight nuts and bolts. Likewise, avoid long 12-point sockets with the breaker bar, preferring short thick 6-point sockets instead.


Impact sockets (coloured black and 6-point)
Photo: Courtesy of Craftsman


A pair of padded mechanics gloves to reduce skinned knuckles is advisable to stop the hammer being deployed as self-soothing mechanism. Finally, before applying a tool to the bolt it is worth remembering the old mechanic's proverb "Righty-Tighty, Lefty-Loosey". It is ever so easy to get spatial directions confused when working in a reversed or upside down position common in boats.


Releasing a seized bolt
Photo: CC0


Getting Started

Sometimes nuts and bolts can be removed by first attempting to tighten them so that they 'bite' on clean threads but if it is already on very tight this will not work.


Impact Driver also known as impact wrench or screwdriver
Photo: Michael Harpur


Give the bolt a good thump of a hammer first to knock the rust loose and free it up, but not hard enough to distort or burr the bolt top. If it is a screw and you have a large, old and solid screwdriver, sit it into the slot and strike it with a hammer. The impact may shock the screw in its seat breaking the locking tension. If this does not work there is a specialist tool called an impact driver, occasionally known as an impact wrench or screwdriver, that is specially designed for this purpose.

Shocking a seized bolt free
Photo: Michael Harpur
Shocking a large bolt, such as a keel bolt, may also help. Hold a very heavy hammer or sledgehammer solidly behind one face of the bolt and strike it with a hammer on the opposite side as illustrated. The jarring shock usually loosens the nut.

Use a breaker bar to give you more leverage and use a steady even pressure paying close attention to the feel of each turn. Tap the breaker bar with a hammer to try shock the fixing. If it is a big heavy bolt extend and add leverage to a breaker bar or spanner by inserting a pipe over it and using it as an extension. If you do not have a pipe to apply leverage you can achieve this by interlocking two combination wrenches to apply additional leverage.

The length of a ring spanner’s arm is specifically designed so that in normal use a bolt cannot be over tightened. Likewise, you should not extend the spanner’s leverage to tighten bolts and equally you should be restrained with a spanner when using smaller diameter fittings or working softer materials such as brass.

Another approach is to strike the body of the bolt from above with a copper headed hammer whilst someone else is applying a turning movement on the nut with a wrench. If you have not got a copper hammer, or the hammer is too wide to strike the bolt, use a brass drift to avoid the hard face of hammerhead striking and riveting the bolt.


Adding leverage to spanners to open seized bolts
Photo: Tony Gibson


In all cases, watch closely to make certain the wrench or spanner is not slipping over the flats of the nuts. Remember, do not overdo it if it is not releasing. If the tension suddenly becomes soft or rubbery, you are either breaking the bolt or stripping the threads.


Clean It Up And Soak The Threads

There is some doubt as to the the usefulness of penetrating oil but in most cases, testing has shown penetrating oil can reduce the torque required to overcome the rust bond by up to half or more. First use a little elbow grease with a stiff wire brush and remove as much rust off the threads as possible. Then liberally soak the threads with a penetrating oil.

Many people turn to WD40 as the solution to all needs but in this case, it is of little help being a Water Dispersant and not a penetrating liquid. There are many different brands to choose from. Many swear by 'Plus Gas Formula A' dismantling lubricant. However, a homemade 50/50 mixture of Acetone and Auto transmission fluid (light oil) is as good as any, better than most, & cheaper than all. Don't get it near plastic as the acetone will melt it and be mindful of the fumes. If it needs to be used near plastic try a 50/50 mixture Diesel and transmission fluid which is also very good.

Play dough creating a lake of penetrating oil over seized bolt
Photo: Michael Harpur
Simply spray the problem area and allow five minutes for the penetrant to work. By tapping lightly on the nut or bolt you can help to break some of the areas bonded by oxidation. If the bolt still doesn’t turn, reapply again and wait 10 more minutes. If there’s no luck, soak it overnight. If the stubborn bolt is on the flat, children’s play dough can assist the process by creating a damn so that a lake of penetrating oil may sit around the bolt which will work its way down in time.

Just be aware badly seized parts may need to be soaked for a few days and you may need to repeat applications for a few days or even weeks. Remember, patience is key and it can save you hours spent drilling out a broken bolt.


Apply Heat

Any kind of warming will help free up a bolt, but it can also do serious damage to surrounding components so extra care must be exercised. Paint and undercoating will almost always burn away before the bolt turns loose and sheet metal can easily deform under high temperatures. So the heat has to be used with extreme caution. If you are heating in an area that has fibreglass or wood nearby place a quantity of protective wet rags around them so that the heat is dissipated and does not cause any damage.


Off the shelf portable butane and propane gas torch
Photo: Michael Harpur


Household blow torches with a stable and rugged flame, used for most DIY jobs around the house, are an excellent source for the focused heat required. Butane, however, burns cool and for large bolts, such as in an engine block, you may need to go for a propane torch found in most workshops.

The objective is to bring the part up to a dull red colour. Try to focus the heat on the nut and not the bolt. This will allow the nut to grow slightly larger expanding itself away from the threads of the bolt. Once this happens the molecular bond fixing the bolts threads in place should break. The heating and cooling action fractionally expands the metals at different rates helping to break the metals apart. Don’t apply too much heat as it can cause the fastener to soften its temper and perhaps break off.

Once the seized bolt has attained a dull red heat then immediately place a domestic candlestick over it so as to melt its paraffin based wax onto the threads. The cooling process then tends to draw the wax, which melts into a thin liquid, into the threads. The wax will tend to flow to the heat source, so heat the bottom threads the most. After it has cooled down the bolt or nut should then undo. Sometimes two or more applications of heat will be needed.

If you do not happen to have a candle simply heating and then dousing with cold water can sometimes loosen stubborn fittings as it causes expansion and rapid contraction.


Impact Driver

½ Inch impact drive
Photo: Courtesy of Kawasaki
An impact driver is designed to strike down with a hammer action as it also imparts a turning movement.

Small electric impact guns are available today that are portable and easy to deploy. But an impact driver should be the tool of last resort for larger bolts because they can so often break the bolt off. They may only be used if the seized bolt is set in a fairly solid area, in good condition and has a purpose made socket, normally 6-point and coloured black as above, that fits well.

Wear gloves and safety glasses when using the gun, and if possible, use the impact on the nut side and hold the bolt with a wrench.






Destroy the Nut

If it is still frozen in place after all that the next step is to try and safely break off the nut but preserve the threads beneath. Smaller nuts that are rusted or seized can be removed by using a purpose made Nut Splitter. This is a special tool used to break the damaged nut without damaging the bolt threads.

12-16mm nut splitter
Photo: Courtesy of Laser
Nut Splitters are like a small c-clamp but very sturdy. It latches on to the nut from the top, then is tightened with a spanner to fit right onto it applying mechanical advantage to drive an angled point into the nut. From there you can either use the splitter for extra leverage to loosen and ratchet the nut free, or you can keep tightening until it splits the nut on one side. If it still does not come off then repeat the process on the other side to break it in half without mangling the thread up too badly.

The problem with a Nut Splitter is that it might not fit into the tight area where the nut is. If you can get it on the nut properly they will work. You also need to select an appropriate nut splitter for the nut you want to remove. This means you will have to buy a nut splitter of a suitable size for the nut as well as a design capable of giving you access. A replacement nut/bolt will, of course, have to be found, but if done carefully the bolt may be undamaged.

If none of the above are available the nut can be drilled and split. Done carefully this will leave the bolt undamaged. If the nut is on a flat surface it might be possible to use a hacksaw and cut the nut by sawing down close to the bolt. Applying heat makes this an easier task.

When it comes right down to it, the best tool you can use to remove a seized bolt is determination. Don’t give up and use everything at your disposal. Try multiple combinations of these techniques and eventually you will get the job done, even if that means having to replace the bolt in question. If you want to avoid this happening in the future try applying anti-seize lubricant to protects metal parts from rust, corrosion & galling. There are many products available with some resistant to temperatures up to 1000°C. The below video Best Ways to Get Rusty Nuts and Bolts Off (Effective Techniques) may also provide some additional ideas.

But if it has completely sheared off, it is not the end of the world as a sheared off bolt may be released by welding.

With thanks to:
Michael Harpur, Yacht Obsession.




Best Ways to Get Rusty Nuts and Bolts Off (Effective Techniques)



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