Fitting Welch Plugs
Fitting welch plug with special internal fitting tool
ENGINE ASSEMBLY HINTS
Fitting Welsh plugs and oil gallery plugs…… selection of Welsh plugs will depend upon the application. Diesel engines should use stainless steel as erosion seems to be more prominent than in petrol engines. Brass Welsh plugs are a good choice for most applications. The life of plain steel Welsh plugs will depend upon the quality of the Welsh plug and the maintenance of the inhibitor at the correct levels.
When fitting Welsh plugs ensure the block is not damaged. Emery finish the Welsh plug hole if minor damage or foreign material is evident.(hard sealer or rust etc). Use a suitable sealer such as aviation gasket goo. When fitting saucer type Welsh plugs such as the camshaft plug in some V8’s.use a solid flat punch to flatten 2/3’s of the dome area in the centre only. Don’t reshape from convex to concave, just go to flat as at this point maximum size and sealing pressure has been achieved. Don’t use the ball of a hammer to butcher the plug into submission as the quality of the seal will be suspect. SIMPLY NEATLY FLATTEN 2/3’S OF THE DOME AREA IN THE CENTRE, STAYING AWAY FROM THE SEALING EDGE.
Fitting cup Welsh plugs…… Special tools are available to fit cup Welsh plugs. These may be OK, but I have no faith in them. These tools rely upon contact with the outer edge or sealing area of the plug. If you look at a modern style cup welsh plug you will notice that the sealing ring is only around 1 to 2 mm wide on the very outer edge. Any slight burr or mark on a tool that contacts the sealing edge will result in a coolant leak. These fitting tools may be OK while brand new but I prefer to use a good internal fitting tool. My advice is to never fit welsh plugs using the sealing outer edge. Select a tool that has around 0.5mm. clearance on the inside of the cup. Use a good quality sealant. Squarely and firmly hammer the welsh plug to flush with the inner edge of the fitting chamfer. This method has been reliable and has had 100% success against leaks over a 25 year period.
Threaded welsh or gallery plugs…… These are very easily sealed with a good sealant. Don’t use thread tape.
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