Core Plug Sizes and Material

[John P]

I have a leaking core plug (Welch Plug) at the front of the block and am thinking of getting some stainless steel ones as they only seem to last a couple of years despite always using anti-freeze in the coolant.

As the supplier isn't an Austin 7 specialist I need to provide the sizes but it's quite difficult to measure accurately with the drive gear housing still in place.

I believe the large one is probably 1 5/6" diameter but the smaller one looks like it may be 5/8" diameter.

Could anyone confirm these sizes and I also wondered what the general feeling was about using stainless or even brass welch plugs.

John.

[Robert Leigh]

I would think stainless stel core plugs would be very satisfactory. I imaging that mild steel have normally been used for cheapness. I suspect that modern ones are thinner than the originals because they seem to fail more quickly. I always use stainless studs for securing water joints to the block and head, with stainless or brass dome nuts and fibre washers. This prevents water leakage up threads.

[Colin Morgan]

Core plugs are 3/4" and 1 5/16" as per references below:

https://www.theaustinsevenworkshop.com/p...g-knock-in

https://www.theaustinsevenworkshop.com/p...g-knock-in

As you know, they are precisely made in a dished form so they can be knocked into place and seal - this needs a malleable material like mild steel.  To reduce corrosion I have known them to be 'tinned' with solder prior to fitting, but those in my engine have done over 20 years already without tinning.

[dickie65]

I smear the inside of core plugs with sealant.

[John P]

As a rather belated follow up I eventually bought some stainless steel plugs from Core Plugs International (coreplugs.co.uk) who can also supply some sizes in brass.

A complete set of 2 large and 5 small cost a total of £15.08 including VAT and carriage.   A bit dearer than mild steel but if it avoids future problems then it's well worth it.

Out of interest they recommend using Hylosil instant gasket (RTV Silicone) when fitting them but I actually used Hylomar because it's what I had.

John.

[Parazine]

I always use Green Hermatite on core plugs. 

When was the last time you saw that on sale?!

[Charles P]

I always use Green Hermatite on core plugs. 

When was the last time you saw that on sale?!

Years since I saw it.

Heldite is the replacement I use. Excellent for more permanent applications 
https://www.rustins.ltd/heldite/our-prod...g-compound

[Ivor Hawkins]

I second that, I’ve just replaced a core plug in the head that had rotted through and I use Heldite every time.