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A beginner's question on core plugs


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Hi there,

on my 37 Roadmaster I am considering to remove the engine core plugs in order to remove scale and other stuff inside the engine block that may be the root cause for overheating.

Now, the engine looks like it had got a pretty paint job and the core plugs have been painted over.

What is the best way to remove them without causing further damage?

And how do I get new pugs to fit in tightly? Do I have to use some special sealant?

Thanks as always,


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Crude but effective...; usually they are removed by punching a screwdriver into the center and prying them out. You might want to score the paint around each one and use a block to pry against to prevent chipping the engine paint.

You can get virtually any size replacement at your local auto parts store.

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A screw driver is for driving screws. A chisel either pointed or narrow would be a more appropiate tool. All you need is one screwdriver to disintegrate into your hand or face (both in my case) when you hit it with a hammer and you always remember to use the proper tool for the job. We ae not like some reptiles we don't grow new parts.

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Guest 1937RHDNZ

I feel that I am this weeks self confessed expert on replacing frost, welsh, core plugs, as I replaced my rusted out ones with new brass versions a matter of days ago. My small block plugs were 1 15/16ths, from the master parts list '404169' it appears that this is the same size for the big block as well for years 1936 to 1941, you should be able to get them easily.

You will need to remove the manifolds to do the job properly. If the existing plugs are brass and in good shape, then you may be able to get the 2 end plugs out, without removing the manifolds.

I used a specially sharpened small cold chisel, the head size being 8mm across. Place your very sharp chisel on a slight angle inside the edge at the bottom of the cup, hammer it until it goes right through the metal. Continue cutting at least half way round like open opening a tin of spagetti (or whatever). Bash the half round flap out of the way a bit. Then using a blunt wider piece of metal hammer inside the cup opposite to the gash you have just cut. With a bit of luck the plug will move inwards (don't panic it can't go far) and spin on its axis, exposing an edge that you can then pry out. The object of this method is avoid hitting the block directly at any stage. Avoid using a hacksaw blade to cut the plug as this can cut into the block.

Once you have the 3 out, begin flushing, pick you vehicle spot carefully as rusty muck goes everywhere for ages. I spent about a hour flushing with a hose until I could get the water to run clear. A lot of muck accumulated near the firewall end of the block, you have to pick it out by hand.

When all flushed clean the surface the the plugs go into. I used a thin layer of ABRO Eagle Shellac on the mating sufaces. I didn't have the proper drift to drive the plugs in, so used a large 1/2" drive socket that just fitted snuggly inside the cup, and drove them home with ease.


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Guest Andynator

Neil, very nicely written up.

I petition for a "How To" forum with sticky topics for things like this. Anyone else?


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