In this article we are going to take a look at what is involved in replacing welch plugs, otherwise known as freeze plugs, expansion plugs or welsh plugs with an ‘s’.
What we are doing with this article is covering only the actual removal and replacement of a welch plug itself on a scrap engine, there are too many variations to be able to accurately cover what has to be removed before gaining access to the plugs so I will have to leave that up to you (for example – on 6 cylinder Falcon engines the exhaust manifold needs to be removed to gain access to the main welch plugs). For the time-being anyway, I hope to have detailed welch plug replacement articles done for the more popular engines some time in the not-too-distant future.
Ok, on with the show. The first thing you will need is replacement welch plugs of the right size (if possible check the sizing of the new against the old before fitting), a punch or drift, a hammer, some sealant (more on that in a moment), some emery tape or sandpaper, a small mirror if you have one, a set of pliers or vice grips and a socket or tube that fits snugly inside the new plug.
To remove the old plugs it is simply a matter of picking one side and knocking it in with the punch and hammer. The ideal situation is where it ‘turns’ so that the opposite side comes out – this doesn’t always happen though and don’t stress if the plug goes into the block instead of one side coming out.
After a bit of punch and hammer work you should be able to grab one side with the pliers or vice grips (multi-grips work too). With a bit of effort you should be able to pull the offending welch plug out from it’s hole.
Next up we need to ensure that the new plug will have a clean surface to seal against. Here we use the emery tape or sandpaper and run around the edge of the block to clean up any rubbish. Having a small mirror to check your work at this stage is handy.
Once you are satisfied that everything is good it’s time to check the new plug’s size and if that looks good it’s time to run some sealant around the outside edge of the new plug. My personal preference here is Stag Jointing Paste (available at Repco, Super Cheap etc), but I know of a few people that prefer to use a non-hardening sealant such as Aviation Form-A-Gasket (also available at Repco, Super Cheap etc). I can tell you that I have never had a replacement welch plug leak using the Stag but I’m sure either one will do.
Once the sealant is in place, take the socket or tube and fit the new plug up to the block. The idea here is to evenly knock the plug in until it sits just inside the ‘lip’ of the hole in the block (a mm or two below the block surface).
You should get a good idea of where it is supposed to sit from looking at where the old plug sat before you removed it. Running your finger around the edge will give you a good idea if the new plug is seated evenly or not.
Now you can wipe off any excess sealant and go on to the next one.