Oil Gallery Plugs – How To Remove From Lotus Twin Cam Engine Block.

When the time arrives for the big engine overhaul and rebuild, there are so many things that need to be removed, checked and cleaned, quite often it is very easy to overlook the small but important things. One of the most important items on the list during a complete engine dismantle is to remove and clean every oil gallery and cross drilling in the engine block.

Failure to carry out this simple cleaning procedure could undo all of the best efforts of an extensive engine rebuild within the first few minutes after start up of the rebuilt engine. But there are many times when the the removal of gallery plugs can be forgotten, or they are left for another time, or, in some cases the removal of the plugs is attempted, but they are found to be so stubborn to undo that they are left undisturbed in the block, and that means all of the muck and sludge that is left in the galleries is sitting there ready to be collected by fresh engine oil and pushed through the new bearings after start-up! Even if plugs are not removed from the engine block, hot tank cleaning will not remove all of the muck in the galleries.

If you have been guilty of not removing the oil gallery plugs, then you are not alone, many people do the same because of the difficulty of removal, yes I know what you are thinking, they are just simple screw in items, surely they come out easy. Well the experience is that if a previous mechanic has inserted the plugs with far to much torque, they wont come out by just inserting a hex key and unscrewing them. The plugs are 1/4″ BSP tapered, and over time, as the engine block expands and contracts with heat and cold, the plugs tend to lock in very tight, kind of like they are frozen in.

It is not unusual to have the hex key simply twist and break while trying to undo the plugs, or the in hex shape in the plug will be stripped, or both will happen.

So what’s the answer?
Intense Heat.

The application of 3000C deg heat from a small Oxy/Acet welding tip will do the job… but there’s a neat technique to this.

You might be tempted to use a small butane or plumbers gas torch, but the heat from those devices most likely wont cut the mustard for the job, that’s why the Oxy/Acet is so good, because it can apply intense heat on the plug in a very short time frame without doing any damage.

The idea is to apply heat to the small part of the plug protruding from the engine block, direct the flame into the hex hole at the top edge but at a 45deg angle, on one side, then the other in quick succession, the moment you notice the edge of the plug becoming red hot, stop the heating process, that is all that is required.

Allow the metal to cool, the surrounding cast iron will be warm but not hot, and don’t worry everything, you wont harm the cast iron, there is far to much metal surrounding the plug, but the plug must be cold before attempting to undo the plug. Squirt a small amount of CRC onto the plug as it cools, then insert the hex key and unscrew anticlockwise, and voila the plug should now unscrew.

If it fails to unscrew, apply another heat treatment with the torch, then place a rag saturated with cold water onto the plug. The heating and cooling of the plug activates a shrinking moment within the metal, that is the trick to removing stubborn oil gallery plugs.  Like many things, it is easy when you know how.

If any of the plugs have been damaged  during removal attempts they should be replaced, and when inserting the plugs don’t over tighten them, apply the correct Loktite thread locker which will prevent any leaks and prevent the plugs undoing.

You may be wondering where new 1/4″ BSP gallery plugs can be obtained? Yes your performance shop should have them, but if not, contact the nearest hydraulic supply or repair shop, as they are a common standard repair item in the oil hydraulic business. Most new gallery plugs will have metric hex drive, the plugs above are 7mm, and make sure to use the correct key otherwise damage could result.