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MG MGB Technical - Core plugs

I've got a leaking (well more a slow weeping - just damp) core plug on my MG’s engine. I guess it’s in need of long term replacement but I’m not able to do this in the short term.

Question is how long can you run the engine with a weeping plug? It’s not losing coolant so the question is, is it likely to pop out. I know this is a un answerable question but would appreciate some advice. Has anybody experience of a similar problem and what did you do.

1980 mgb roadster.
Brian Davis

Is it on the side, or on the back?
Dave O'Neill 2

Dave.

On the side of the block. It's the middle one of the 3.

I'm going to leave the engine in when I change it but will have to remove the Dizzy and oil filter to get to the old one and to get something onto the new one to pop into position.

Any tips on how to do would be appreciated.

Brian
Brian Davis

Here's another question (or maybe i've just missed something). Why do they sell sets of core plugs in 4's when I can only find 3 on my engine.

Brian
Brian Davis

Three on the side, one on the back, hence Dave's question.

Middle on the side are easy to change, BT, DT. Flat or cup-shaped? Although I don't think it matters that much.
paulh4

Paul

Thanks for that. Didn't think about the back of the engine.

The plugs as installed are flat. I've ordered new ones from BHive, they are convexed as they come. I assume they flatted off when knocked into the hole in the block.

How do you get the old one's out? Punch a hole in it and prise out?

I also assume that to get the new one's in and flattened you use a drift/punch and that the flattening off of the plug seals them into the hole in the block.

Brian
Brian Davis

Mine are cup as it's a Gold Seal and they convert them as part of that process. The flat can get pinged out from the shockwaves from detonation, apparently.

I just punched through and levered out as you say. Clean out the recess, put sealant round. I've not done flat but I believe you should use some kind of a drift not that much smaller than the plug, so they are flattened before there is any tendency to bulge the other way. Flattening them expands them into the hole. Too small an impact surface could start to bow the centre in while the outer part is still bowed out.
paulh4

If you do replace all of them, I strongly recommend adding a Betson bolt to the rear plug. This plug has a tendency to pop out and it is a bugger to replace.

The Betson bolt is a bolt that goes through the rear plate (there is a hole in the plate right in back of the plug) and puts pressure on the plug, keeping it in place.

Here is what I built, but you can use a nut on either side of the plate to push the bolt against the plug.


Bruce Cunha

Here is a picture of it installed


Bruce Cunha

This thread was discussed between 12/10/2019 and 14/10/2019

MG MGB Technical index

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