Marine Diesel Engines by Peter Caplen

Author:Peter Caplen
Language: eng
Format: mobi, epub
Publisher: Crowood
Published: 2011-05-17T00:00:00+00:00

This is an expensive and time-consuming task that can be easily avoided by early precautionary measures. From the foregoing it is easy to understand the important role that the humble expansion plug performs. Unfortunately the light construction of these plugs makes them a prime target for corrosion, and in time they will eventually begin to leak, at which point they should be replaced.

This is normally a straightforward job, except where the plug is situated in an inaccessible position, such as behind the flywheel. In this case the gearbox will need to be removed, followed by the flywheel housing and flywheel before replacement can take place. In this case a temporary repair can often be achieved by using one of the leak remedies that are poured into the cooling system, and plug the gap from the inside.

Happily the rest of the plugs are more accessible, and replacement does not take long. Each plug is in the form of a dished cup and is an interference fit in its bore; they are generally in stock sizes, and can be bought in sets from most car accessory shops. To remove the old plug it should be lightly tapped inwards to break the seal of corrosion and sediment deposits, which will have built up over a long period.

Care must be taken to ensure that the plug is not tapped right into the block, or an interesting half hour will be spent trying to fish it out again. To prevent this happening it is a good idea to drill a hole through the centre of the plug and pass a hooked item (such as an Allen key) through the plug. This can also be used to assist in pulling the plug out once it has become free.

Once it begins to move it can be tapped on one side to turn it sideways in its bore, at which point it will be possible to pull it out with either the hook or a pair of pliers. Never attempt to prise it out against the face of the bore, as this will damage the seal surface between the plug and the block and may lead to further leaks.

Once the plug is removed, the bore may be lightly cleaned using fine emery cloth to remove all the old sediment residue. The new plug should be lightly smeared with gasket cement around the outside of the sealing surface, and then lightly tapped into position using the same drift as was used to loosen the old plug. When it is almost home, use a smaller diameter soft drift in the centre of the plug so that the convex surface causes a slight expansion of the seal as it is tapped home, making an effective seal. When the plug is properly located, the seal sides should be flush with the face of the bore in the block.

Should the new plug show tendencies to weep after fitting, this will usually stop after a few hours; if it doesn’t, using one of the

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