mk1-forum.net

That's because you've got an S/Smallbore block.

Here's a reasonable guide with pictures

http://www.spriteparts.com.au/tech/welch.html

That's great, thanks for that.
I've done A+ 1275 before and was worried I'd put them in wrong, but the guide explained that. Afterall, that was 20 years ago and it is still going strong.
Derek

Now I am confused as my AEG151 block does not have the step / recess in the core plug hole.
So in this case is it fitted the other way round like the picture and A+?
What is the best way to fit this type?

Ah, OK, they are the Cup Type, which I've not seen in a S Block before.

Similar proceedure to the Lens Type, only no flattening required.

Clean and Loctite as per previous, however to fit them I use a Socket on a short extension which is just big enough to be an almost snug fit inside the cup, you don't want it snug or the socket may end up being part of the block! Knock in until they top edge is flush with the bock, wipe excess loctite, job done.

If you do use a Socket, with I've made mention not to use one that's not too snug, it also not a good idea to use one that's too small as it may cause the OD to contract which mat result in a leak or having it fall out

Apologies, it's been a while since I last looked at an S Block, yes, they do all have Cup type plugs.