Welch plug replacement

[muzza49]

Can I replace the middle welch plug on the exhaust side, by just removing the manifolds and no engine out ?
I understand that you have to get the plug in situ, convex side out, and then give it a good "tap".
Should I also use a "sealant" too ?
Any words of wisdom appreciated.
Thanks.

[cass3958]

I replaced all mine with the engine out so cannot comment on fitting it in situ but I think it is possible with the exhaust manifolds removed. Might be a bit tight to swing a hammer but it is not so much power as finesse you need as those plugs are difficult to start but once started are easy to tap in. I did not use any sealant as they are a very tight fit but make sure that you clean the area properly before fitting. Having the engine out allowed me to get a wire brush on a drill in to clean all the old rusty material out of the hole. You can buy a cheap 90 degree attachment for a power drill so you can get into the plug hole.
As you are replacing a plug I would take the opportunity to really flush out the water jacket in the block using the vacant plug hole. Get a fast powerful jet of water into the hole and flush the block out. Over the years you might find that previous owners have used Radweld or similar products to mend slight leaks in the radiators or from these Welch plugs when they seep. It is horrible stuff that gunks up the waterways and can be the main cause of our old engines overheating. A good flush with a powerful running hose will clear 90% of the stuff out and allow your engine to run cooler. You will also be surprised at the colour of the water you will flush out and how much rust particles will be inside the block.

[John Quilter]

Good suggestions by Rob C. Forty five years ago I did replace a plug on my S Type with the engine insitu and the manifold (s) off so it can be done. I think there are other types of plugs that are part rubber and have a bolt that you turn to cause it to swell up and seal. Not had experience with them though.