Quite often, when removing the cylinder block, the studs break off. There are many ways to solve it, but it must be admitted that not all of them are equally good. It would be possible to use an extractor to extract broken hardware, but even he is not always able to cope with the task at hand. The question can be solved by welding the bolt, however, this method is fraught with fracture of the entire block. Therefore, it is best to remove the debris chemically.
What you need: citric acid, a set of drills, a dropper, a dry air heating element 1 kW (or more), a syringe, a thermostat with a remote sensor.
The center of the piece is drilled out with a drill and a thin drill. The hole is made to the full depth of the hardware. After that, it is expanded with a larger diameter drill. The passes are made with an increase of 1 mm. This is to keep the risk of drill breakage to a minimum. The hole is widened until the bolt is fully drilled. Only its thread should remain in the problem area.
Important: Under no circumstances should the drill hook the thread of the block itself during operation!
When the drilling is finished, prepare a citric acid solution, and then immediately pour it into the resulting hole. The liquid will gradually evaporate, for this reason it is necessary to use a dropper and periodically replenish the amount in the hole, so that it covers the entire thread.
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Simultaneously with the supply of the solution, it is necessary to carry out one more operation, namely, to heat the block. To do this, you can apply a dry type heating element to it. It is imperative to connect it through the thermostat. The sensor is lowered into the adjacent pin hole. The temperature must be set at 80 degrees.
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In this case, the cylinders must be covered with oiled paper. This is necessary so that citric acid does not get into them. In this form, the entire block leaves for 1-2 days. You will also periodically have to choose an acid with a syringe and pour a new solution in its place. This should be done because citric acid will weaken over time.
The chemical method is quite expensive and time consuming, but at the same time it remains one of the most reliable and effective.
Continuing the topic, read about how to restore a broken thread in a plastic product in minutes.
A source: https://novate.ru/blogs/100220/53390/