Welch Plugs
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Welch Plugs - Filling a hole
A welch plug is a cupped mild steel or brass piece of metal that is designed to fill a hole left by a casting or machining process. They are commonly found in engine blocks or cylinder heads. They are a press fit and need to be driven out or into the hole they fill. Some performance engines have screw in ones as they are under more strain than a road going engine.
Why do you need to replace a Welch Plug?
When a large component like an engine block is cast, they need to get the casting sand out of the block easily. Most engines use water cooling around the cylinders and it is these areas that are filled with sand when the molten metal is poured into the mould. Once the metal solidifies, it would be hard to get the sand out via the normal water passages.
To help, they leave holes in the side of the block. This makes getting the sand out easier though it leaves a big hole when trying to fill it with water. The welch plug is designed to fill and seal these holes. Most manufacturers use mild steel plugs when building engines. These will eventually rust if the water or coolant is not looked after and begin to leak.
Luckily the replacements these days are brass so will probably last you longer than the engine. If you have an engine with a leaking welch plug it is a good idea to try and replace all of them. Chances are if one has failed the others may not be too far behind. While welch plugs are cheap, the labour involved to get to them can be expensive as you may need to pull the motor out of the vehicle.
The only thing you need to worry about is buying the correct size welch plug for your engine. At Repco, we have a range of brass welch plugs in various metric and imperial sizes.
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