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MG MGA - Head gasket and core plug

Yesterday I had a major breakdown but for my son in law not myself. The symptoms were lots of smoke from under bonnet and major loss of power. When I got there the the starter was dead too. By the way the engine is a 3 bearing early MGB unit.

When I got car home I found the middle core plug had gone and the head gasket had failed between cylinders 3 and 4. Also before dismantling I tested compression and it was 60 on cylinders 1 and 2 and 30 on cylinders 3 and 4. Also at home starter worked so I think this just got too wet to work when core plug above it failed.

I suppose I am asking for comments on -
1) While I understand compression being 75% down on 3 and 4 why was it also down on 1 and 2 where gasket was fine. Can anyone explain this?
2) Any helpful comments on replacing middle side core plug?
3) I believe some gaskets are better than others. Which are best and who can supply them in UK?
4)Anything special I need to do to prepare head and gasket surfaces where gasket failed. Clearly it went where there is very little gasket on a bored out 1800 unit.

Over to you all.

Paul
Paul Dean

Hi Paul,
head gasket failures are a real pain, because you know that it is going to take quite a few hours of workshop time to fix it.

I have used PAYEN (multilayer) head gaskets since I had a COMETIC (multilayer) gasket fail a few years ago and I have no problems since then,(Touch-wood).

Unfortunately, I understand that PAYEN gaskets are not easy to find just now.

When you checked the compressions, did you jam the accelerator pedal down to make sure the throttles were fully open?
(A friend of mine who was a mechanic, rebuilt a customers engine which had low compression readings, only to find that there was no improvement afterwards.

Once he re-tested the compressions with the throttles wide open, the pressures improved dramatically! I never did find out if he told his customer about this!)

I have been fortunate enough (so far) to have avoided having to replace a core-plug and so I can't help there. The core-plugs on my 1950 cc 5-bearing engine have a bar which is screwed down to the block which hold the core-plugs down.

Also, it would be worth checking the block to make sure it is perfectly flat, particularly where the gasket failed.

Let us know how you get on Paul.

Cheers
Colyn



Colyn Firth

First task achieved, I have ordered a Payen gasket from MGB Hive. After several google searches didn't come up with anything a name I knew came up, never dealt with them before.

It is amazing they ever work on 1800s at +40 with so little metal between the siamesed cylinders 1 and2, and 3 and 4.

Paul
Paul Dean

Paul,
this may only apply to A-series Payen BK450 gaskets at a certain time be aware on the midget & Sprite side, two years ago, I got a Payen gasket from Mini Spares so they should have had reasonable stock turnover and it had a sticker on it as below, I thought it was just general advice from Mini Spares - but - later -

Alan Anstead, Kent, United Kingdom - Posted 03 January 2021
"I recently built a half engine for someone leaving them to fit the head and refit in the car. They fitted a Payen HG and torqued before going off to bed. Going back to the engine in the morning the sump had water in it. Phoning Payen revealed a known fault and advice to fit, torque, heat cycle, and retorque in succession. To date the second HG has held."

Perhaps Payen were at the end of run before the company was takeover by another company (I forget the details now).





Nigel Atkins

MGB Hive are a great company to deal with Paul, they are my brother in laws "go-to" company for all of his MGB spares.
They swapped a couple of alternators for him without any query when he had accidentally burnt out the voltage regulators on both of them.

I have bought quite a few bits from them too.

Let us know how the head gasket swap goes.

Cheers
Colyn
Colyn Firth

Good progress as head now back on but here are some points.
1) I got Payen gaskets from MGB Hive. My engine is a 3 bearing B unit.
2) They do not carry the warning Nigel showed but I will do as that warning says, thanks Nigel.
3) When I got the head on the bench I tested it for flatness and it seemed to be 4 thou out. So I rang Cameron Gilmour who built both my fairly standard engine and Colyn’s awesome unit. He said yes it does need skimming and in the end it needed 10 thou off. He did the job in under 24 hours.
4) Interesting he could explain exactly what had happened particularly when I told him about the middle core plug coming out. He says this is classic for a B series engine that has the timing too far advanced and it is always the middle cor plug that pops. Also he said he could see how the gasket had burnt through from pinking, another reason to skim the head.. He also said this is common event for racing engines and when he is building racing unit he screw a strap across the core plugs. I told him the engine had been running (too) superbly which is another pointer to the issue.
5)Also he said while you have the head off, and can see the pistons, check the timing pointer are correct as they often aren’t. Mine were about 2 degrees out.
6) Colyn, Cameron sends his regards. For those who don’t know him Cameron, who is near Dundee, only does engines many of which are specialist units. He has worked purely on engines since he left school several decades. Also he uses Payen gaskets and had several in stock.

Paul



Paul Dean

Quite a bit has happened on this saga since my last post on 4 Sept. With the ridiculously low compression readings I first tried a different gauge but no change. Next I spoke to Cameron. He first suggested tappets setting were seriously wrong but I had reset them then he suggested it was most likely valves, as I had head off he suggested putting some petrol in valves to test valve seals. This was dramatic as the petrol poured out of the inlet valves and trickled out of the exhaust valves so head went back to Cameron where his tester confirmed issue so he stripped head changed guides and reground valves. With this done car started and ran.

While I had head off he also suggested putting some engine oil in bores and see if level held overnight as he was also concerned about rings or possible piston damage. In the end oil stayed there 4 days and oil level had pretty well held on cylinders 1 to 3 but had gone down on 4. I have since confirmed with compression tester that cylinders 1 to 3 read 165 and 4 reads 148. Im leaving this as is for now knowing I probably have a ring problem on cylinder 4.

This isnt quite the end of the saga as the water temperature gauge has stopped working presumably because of high air temps in engine once water had gone through core plug.

Throughout Camerons view had been it had been a pretty dramatic blow up and the message for all is be very cautious about advancing the ignition to get that last bit of performance. First thing I did before starting engine was to wind timing back since when I have reset with meter to more conservative setting. Car is running well.

Probably unrelated but my Flame Thrower coil failed yesterday. Quickly fixed as I carry a spare coil.

Paul

Paul Dean

This thread was discussed between 30/08/2022 and 12/10/2022

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