Freeing Seized Bolts
Seized bolts can turn a routine repair into a major headache. In this article, our contributor shares an unusual-but surprisingly effective -method for freeing seized bolts that goes beyond the usual heat and lube tactics. Whether you’re in the shop or out in the field, this clever technique might save you time, tools, and frustration.
The Problem
From time to time we come across a bolt, nut or pin that has stuck in place due to corrosion. A long “breaker bar” is often the solution, but sometimes this will just result in the part sheering. The next obvious solution is heat, but this isn’t always safe to use due to the surrounding materials e.g. rubber seals, aluminium castings, etc. So, apart from shearing the bolt head or nut off, there is another approach that can work if one is careful and takes one’s time.The Theory
Unscrewing a nut or bolt uses torsion (twisting force.) If we think of a shaft in torsion (e.g. in suspensions and drive shafts) one end is held and the other twisted – an increase in angle between the two results in an increase in resisting force. For the same force a longer shaft will have a proportionately larger angle of rotation. Steel can reverse this rotation when the load is removed without degradation up to a certain level. Above this level it will develop a certain ‘permanent set’ (it doesn’t return to the original angle) but, at some point beyond this, it will shear. Now if we consider a bolt seized in a hole, there is a length between the head and where it is seized, even if this is only a fraction of a millimetre. In reality the force stopping rotation isn’t just at a point or line but spread over a short or long distance along the bolt shank. If the bolt head is subject to a torque below that where the permanent set occurs, part of the shank of the bolt will twist in the hole. The amount of twist may not initially be visible to the naked eye but will result in a small breaking of the seized area closest to the bolt head. Reversing the torque (i.e. tightening and slackening) gradually moves the point where the seized section starts with a corresponding increase in rotational angle for the same torque.In Practice
The first thing to determine is how much torque can be applied before permanent set occurs… and this will normally be a bit of a ‘wet finger’ guesstimate. A useful starting point will be a workshop manual quoting recommended torque settings for the size and type of bolt used and try it for feel with a torque wrench. Using a solid non-ratchet bar and aiming for the same feel, try to twist the bolt head backwards and forwards using plenty of penetrating oil. Initially there will probably be no apparent movement but the penetrating oil is being encouraged to move along the bolt shank into the seized section. It may take some time (sometimes several minutes) but with patience and plenty of repeated applications of penetrating oil, more and more angular movement should eventually be seen until the bolt freely rotates. Sometimes a little more torque could be needed, but it is better to take more time rather than sheer the bolt. I have used this successfully many times on bolts, nuts, cotter pins, shafts etc. While it may seem a slow process it is normally quicker than shearing a part and having to try to drill it out. It also doesn’t damage the hole as is often the case when trying to drill a broken part out.Article Contributed by Andrew Chapman
Andrew has contributed to the International B Series Tractors Group and a number of instructional files to the International Harvester Club of Great Britain.
© Andrew Chapman & KMP Brand
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