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Releasing seized screws by impact

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What is the issue?
Screws, like almost every fastening, have a tendency to seize up on a sea going vessels. Engine casing bolts can also be set in place very tight making them difficult to loosen and unscrew.

Why address this?
A seized screw can cause major delay and on occasion damage if it has to be dug out. This could present a very challenging situation on an engine casing.

How to address this?
If you have an old large 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.

An impact driver tool may only be used if the fixing is set into a solid object, and not on a light body panel or similar where damage could result. Provided this is the case, an impact driver which would have snapped them off, can move bolts that would normally have required a torque force for release.

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

First off, help the situation as best you can by soaking the threads and applying heat as set out in releasing seized nuts and bolts and then bring the impact driver to the problem. To this screwdriver sized tool fit the appropriate socket head to suit the challenging bolt or screw in question. It is essential that the proper impact socket is used and you should wear gloves and safety glasses. Once the bit is in the stub you place it upon the screw. If possible, use the impact on the nut side and hold the bolt with a wrench. Then you strike the impact driver with a hammer or mallet whilst also applying a slight opening force on the body of the impact wrench.

The hammer strike is translated into a sudden twisting motion at the head of the bolt. Static friction decreases when force is applied in a short burst and the shock and turn of the impact driver will shift highly resistant bolts.

This is an excellent tool to add to the vessels maintenance arsenal as it can also be used with stripped out screw heads to take out immovable screws and with bolt extractors. It takes a little practice to keep the bit directly upon the bolt when you hammer it, but all you should need are one or two clean strikes to get the job done.

Be careful not to confuse this handheld tool with pneumatic impact drivers that are larger to stow, are more expensive, require mains power, and may not be as useful on a boat for the limited occasional use. An electric impact gun should always be seen as the tool of last resort because it often simply breaks the bolt.

With thanks to:
Michael Harpur, Yacht Obsession.

How to use the manual impact driver

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