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MG MGA - Rear core plug replacement

Hi all,
Just run my 1500 A and after a few minutes steam was pouring out of the engine bay ,on inspection the rear core plug has rusted through, is there any way to change it without removing the engine.

David Speak
D M SPEAK

Have you seen this option on MGA Guru David?
http://mgaguru.com/mgtech/cooling/cool_105a.htm

Not so sure that you can get these here in the UK though.

It seems that you can install this without removing the engine, there is also a rubber-plug version that will last for quite a few years.

It could save you from having to take the engine out again.

Cheers
Colyn
Colyn Firth

Those plugs work great, but cannot be installed in that location with the engine in place because the plug is too thick to fit between the block and rear plate, and the hole in the plate is too small to pass a plug through.

The best option other than pulling the engine would be to install a new dished plug with a "betson bolt". Put the plug in place. Then place a thick washer or piece of steel with a hole in it, on the plug side of the rear engine plate. Put the bolt through the hole. Thread a nut on the bolt. Now screw the bolt into the nut until it hits the core plug. Keep turning and the bolt will dimple the plug which seals it. Leave the bolt there as added insurance.

I can't find a photo of any I've done but this came up on a google image search...


Steve Simmons

1500 engine back plates don’t allow the use of the Betson bolt as they don’t have the extended section that 1800 engines have. If one core plug is rusted out, suggest replacing all. Check if they are brass or steel.
Mike
Mike Ellsmore

Whoops, you're right. I was thinking I was in the MGB section. Ignore my last post and definitely use the Dorman Copper expanding plug. I've been using these for a very long time with great results, when replacing dished plugs in-situ.
Steve Simmons

For me, no hesitation. Engine out and do it all properly, cleaning the water galleries while you are at it. As suggested above if one has gone what is the state of the others.

It's winter and lockdown. You are not missing out on much at the moment. At a reasonable pace it's only a couple of days. I have done it in a day. For Dominic about half a day.

Steve
Steve Gyles

My local MG specialist reckoned he could get a 'windy hammer' in there to splay a new core plug. He seemed pretty confident I seem to recollect but have not seen it in action.
AR Terry

There is an alternative product that some folks here in the U.S. have used to replace core plugs. Ideally the engine should be pulled to properly make ready the core openings, but in some cases the repair may be done with the engine in situ. Early Chrysler hemi engine core plugs had similar dimensions to the B series engine, and a custom designed replacement plug for the hemi engine has been installed successfully into MGA engines; I plan on performing the same conversion in the near future. Left image in the first picture shows what these plugs look like and the image on the right shows them installed. Second picture shows some additional machining needed for these core plugs to work; the retaining strap may need some grinding as well. These plugs are not a straight fit, and some who have used them needed to grind the core openings a bit to center the plugs properly, while others did not need to do so, so be prepared to fiddle with the plugs and/or block if you go down this path. Made of stainless steel with teflon O-rings, these plugs should be a lifetime solution, but if O-ring replacement is ever required, you will never need to pull the engine to perform the work. A set of 6 plugs for hemi engines runs over $80, but the vendor sold me just the 4 which I needed.





Nick Kopernik

A couple further thoughts... The Dorman expanding plugs are just as secure as a dished plug that you hammer. And since they use a nut to tighten, if the plug ever leaks you can tighten it again without pulling the engine. The only negative thing about them would be that they don't look totally original.

I always use them on the rear plug in my MGA and both MGBs for the very reason that they can be tightened if necessary. I've never needed to, but I did once on a side plug. It developed a tiny weep and a 1/4 turn of the nut sealed it.
Steve Simmons

Those interested in this thread might like to read this previous post on the B forum

https://mg-cars.org.uk/cgi-bin/or17?runprog=mgbbs&access=&mode=archiveth&subject=71&subjectar=71&thread=2019061109154016437
Mike Ellsmore

Nick
Thanks for posting that-
I like the look of the Hemi plugs
Cheers
willy
William Revit

LOL.

My MGA record setting days (51 minutes from starting the job to having the engine on the floor) are long gone, and have been bettered by others. I was once told by Dr. Betson that he and PB did three engine removals and re-installations in a MGB within two hours when they kept getting rear crank seal leaks on startup. That's the record for those with aspirations to aim for! It's all about practice and having exactly the right tools, and knowing how (and when) to use each of them to get the result. Air / battery tools speed things nicely and I would recommend a cordless ratchet to anyone who still doesn't have one (both of mine came from Lidl and cost around 35€ each).

A few weeks ago I had a Frogeye engine out in 90 minutes, but that's easy compared to an A as once the bonnet is removed the whole lump can be taken out pretty much intact.

I'm with both Steve's. Either the Dormann plugs or the engine out to do it properly. I did a rear plug ONCE by taking out the toe plate and vowed never again. Where a B engine is fitted the Betson Bolt is an excellent alternative if the backplate allows.
Dominic Clancy

Yes, you can do it "DM SPEAK". The same thing happened to me and I developed an effective method to make it easy from inside the car. It has worked properly with no issues since I did it. Some members of the forum who have answered you participated in the topic that I opened and they know my solution, search the historical archive. You do not have to remove the motor and you will save a lot of work.
Gabriel Martínez

I've found it. As you can see, you can install the normal plug in the same way that the sides are installed. Here is the link. If you can't access it, look in the file for the title "Core Plugs"

https://mg-cars.org.uk/cgi-bin/or17?runprog=mgbbs&access=&mode=archiveth&subject=6&subjectar=6&thread=201906261306146195
Gabriel Martínez

Check this posting on MG Experience. Looks like a really good solution to me, especially for the rear core plug.

https://www.mgexp.com/forum/mgb-and-gt-forum.1/freeze-plug-replacement-now-i-have-hemi.2436110/
JL Cheatham

That's the Hemi plug Nick refered to earlier in this thread------looks good
William Revit

Fitting these plugs throughout surely raises the question why were they ever fitted? Presumably MG thought they were necessary in some, albeit rare, situation.

Paul
Paul Dean

They serve two functions. They will pop out if the coolant freezes, hopefully saving the block from cracking. They are also casting holes from the foundry process.
Steve Simmons

Looks like the hemi plug will maybe not pop out due to freezing.
Art Pearse

This thread was discussed between 06/02/2021 and 14/02/2021

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