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MG Midget and Sprite Technical - Head gasket surface discoloration

Having the head off today to investigate an oil leak, the gasket surface show some discoloration, bottom LH corner on the photo.
The bolck has discoloration too, front and rear, visible on the next photo.


Jan Kruber

The discoloration front and rear. As you notice the surfaces are not cleaned up yet, so maybe gasket leftovers are making the appearance more dramatic.
I have not done a compression test. The engine starts, idles and run very nice.


Jan Kruber

What's the white lead cable-tied to the HT lead about?
Nigel Atkins

Jan
To me, first impression---and I don't know much about A series so could well be wrong--

The headgasket appears to be for a 1275 with the 11 headstuds and lacking some coolant holes along that side of the head (where the three rust spots are)

You need a gasket for a 9 stud engine which has 3 more coolant holes one in the centre and one at each end which is where your gasket is forcing coolant out

Can't quite make it out in your pics, is the headgasket still on there, it's got them three rust marks but no holes in the block to line up with them---?????
William Revit

All 1275 gaskets have holes for 11 studs.

I think the ‘rust marks’ are brass plugs.
Dave O'Neill 2

But the engine only has 9--????
Can we get a pic of the block without the gasket on it--and what bore size is it
William Revit

William,
You are looking at the block, the gasket has been removed.

Nigel,
Do you mean the little white lead on the brown generator plus?
Jan Kruber

Yes, sorry, I went to the same optician as Willy, the blue tape threw me.


Nigel Atkins

William
Some pics for you before cleaning


Jan Kruber

And rear


Jan Kruber

And here's a pic for you Nigel. I asume the w/b lead is a leftover from the dynamo, before an alternator was installed. It was so when I took over the midget.


Jan Kruber

Pictures after the clean up of surfaces


Jan Kruber

Block


Jan Kruber

The carbon deposits on the piston crowns look quite soft and oily and quite a lot of accumulation for 5,000. Has it been using oil - other than the leakage that is?
GuyW

Guy, I think there are very much carbon on the cylinder wall above the piston ring area and in the combustion chamber, I would have asked you, thanks for reminding me.
The crowns are not oily but dry actually, maybe they look a little wet now due to cleanup.
I have not refilled oil one single time this year with a driving distance of at least 5000km / 3150 mls. When looking at the oil dipstick over the season, the oil level has only decreased by 2 - 3mm, which in my eyes means a very very low oil consumption, right ? And the resent occurred oil leak has done its best to drain a fraction.....
Am I to generous with oil in the carburettor dashpots? Or do I drive with to fat mixture, or does that not make carbon deposit?
Do I have to remove all carbon deposit? If doing so, debris would fall down between the piston crown and the cylinder wall, right?
What about the combustion chambers and valve heads in the cylinder head
Jan Kruber

I was wondering why you have a different inlet valve in cylinder 2?
Peter Burgess Tuning

Well there speaks a professional! I struggled at first to spot the difference in the valves even after Peter mentions it !
But l had wondered why the #1 exhaust valve appears to have been running much hotter than the rest. I presume all the spark plugs are the same?

Jan, the way to stop getting carbon down between the piston and the cylinder wall is to smear grease around the top edge of the piston before you start. Then any fragments of carbon will stick to the grease. You then turn the engine a little to lower the piston and wipe the grease and any debris off.
GuyW

The penny dropped with you and the valve then Guy :)

I'm glad it was brought up as I was wondering about those valves, the run marks down that cylinder and the carbon on the pistons but couldn't remember if it was just a a hg change 5k-miles ago - plus knowing nothing about engines.

Jan,
you might be too generous with the oil in the carb dashpots but it'd go on to the underside of the bonnet if it was that bad. If you feel suction as you begin to lift the damper then there's enough oil, at that time at least. I don't know about others but I keep the oil level just above the damper bottom cylinder/whotsit when I have the damper screw cap raised just enough to see in the dashpot for the oil level.

Engine oil level, I can’t remember what dipstick and if yours is a converted USA to Europe car(?) but to save me looking again, here's the dipstick measurements we found before (thanks to Keith (KTM Moore) for following initial measurements) -

1275 Spridget dipstick
Note:-
. the dipstick should have a washer and this washer obviously sits between the dipstick flange and the dipstick tube
. the dipstick tube sits 1 and 1/4” (32 mm) out of the engine block
. millimetre measurements are rounded to whole figure

Length of dipstick – (from the underside of flange without washer) to:-
. ‘MAX’ line is 7 and 7/8” – (200 mm)
. ‘MIN’ line is 8 and 11/16” – (221 mm)
. end is 9 and 9/16" – (243 mm)

Distance from the bottom end of the dipstick to:-
. ‘MIN’ line is 7/8" – (22 mm)
. ‘MAX’ line is 1 and 11/16" – (43 mm)
Nigel Atkins

Here we go , hang myself again

I think there is the possibility that , the no2 inlet valve isn't sealing correctly and possibly blowing back in the port causing the lean mixture in no1, shown by the whiter exhaust valve colour on no1 exh valve
William Revit

and , the surfaces are no way near clean enough---yet
You don't need to clean the piston crowns themselves but the combustion chamber in the head is easy to do so why not
As far as the flat surfaces go they need to be spotless---every little piece of anything left there is going to prevent the gasket from sitting down properly--there are pieces of old gasket everywhere on that block, specially round the edges of the bore and up along the outside near the pushrod holes
William Revit

Peter,
The inlet valve was fitted when I ovehauled the engine nearly two years ago. I had the cyl. head in a machine shop for inspection. All brass seats were fine, but the people there showed me that the valve stem was a tiny fraction bend. They skimmed the head and had the valves / seats grinded. I bought a plain valve from Moss and this is what I got.
I do not remember if they skimmed the engine block / head surface.
Guy,
All the spark plugs are the same color, light brown
Nigel,
I read the instruction in the owners manual, as if the oil level in the dashpots should be as high as 1/2" from the top. I allways thought it was a high level, I might have misunderstood the written words...?
But then again, should this small amount accumulate this big amount of deposit.
I would have accepted the amount of deposit if I have had to refill half a gallon for each 1000 mls....
William,
I will check the valves for tightness. Second, I have scraped the surfaces with a long sharp blade. The surfaces are totally plain now. If I have to remove the darker areas too, I will have to use some abbrassive paper / tool. I'm reluctant to do so, the I rather go to the machine shop to have it skimmed again. Easy with the head, but a loooong travel with the block, right?
Jan Kruber

The way we see if the deposits are oil based is to rub the surfaces with a finger, if the deposit comes off on your finger and is dry like charcoal all is well. If the deposits leave an oily smudge then there is oil present and source needs investigating.

The oil level in the carbs, do you mean half an inch from the top of the dashpot or the top of the tube in the piston?

Peter Burgess Tuning

I have understood that the oil level should be half an inch from the top and by the top I think the edge.
Is it 1/2" from the top of the damper tube?
Jan Kruber

Jan, (Peter),
the dashpot oil level descriptions are confusing from different sources and I remember something about 1/2" but when I look in my DH (every night before I sleep) I find my copy has "... to bring the oil level 1 inch (25.4mm) below the top of the suction chamber."

I wasn't suggesting the dashpot oil level would be the cause of your soiling just addressing your question about the dashpot oil level.

As with the dashpot oil level I've found the engine finds its own normal running oil level and it might not be exactly spot on to what the book has or always spot on the 'Max' mark on the dipstick. Once this level has been established I find it a waste to fill above it.

Oil consumption on engines varies so much that I would have seen if kept/refilled to the level it's at now if that level drops and by how much over the same time and use. I'd struggle to see 2mm difference unless it was from the 'Max' and then I wouldn't worry about it.

Anything to do with engines you've got the right contributors - excluding me other than general experience of use.
Nigel Atkins

Jan, just keep it about the length of the plunger valve below the top of the steel piston tube, then it will not spill when you push the plunger home. Are you using engine oil?

Peter Burgess Tuning

William
The valves are all very well sealing, tested them today with some volatile liquid, in this case some Loctite primer liquid. Nothing penetrated.
Jan Kruber

Peter
Until recently I have used the 20w/50 oil as used in the engine (Valvoline VR1). Recently I began using plain 20w damper oil (motorcycle fork oil).... just because I had it on the shelf and I read that Burlen recommend 20w.....
I don't notice any difference though.....
Jan Kruber

By the way, I'm going to clean the gasket surfaces thoroughly tomorrow and torque the cylinder head down.
I have noticed in the Moss Catalogue in the cylinder head section, that a Well Seal gasket compound is shown in the middle of all the parts. There are no arrows to point out where to use it though.
Can someone reveal the secret, please?
Jan Kruber

Put the Wellseal on all the metal parts of the gasket, both sides of the gasket.
Peter
Peter Burgess Tuning

On the metal parts? That was certainly a surprice to me, I thought maybe on the soft parts around the oil drain holes.......
And sealing on the very hot rings surrounding the bores? Please allow me to be surpriced - learning all the time
Jan Kruber

My pleasure for you to be surprised. I think the Wellseal allows the head gasket to move around a little as the torque is applied.
I first came across it in 1987 when a guy building and racing a TR4 used the Wellseal on a steel shim cut out as a head gasket ( thin shim to raise the CR), I then used it on the steel shim head gaskets on 3.5 V8 Rover engines and progressed on to the metal bits on A and B series head gaskets.
Peter Burgess Tuning

Jan, don't be tempted to over torque the head bolts. Doing so will crush the fire rings down and spread the pressure over the whole of the gasket surface, reducing the clamping action from where it is needed. Just use the correct figures, don't "add a bit for good luck".
GuyW

Spot on Guy, we have seen a fair few A series gaskets squashed out and fail!
Peter Burgess Tuning

Peter
Just out of interest
On another thread by Jan-'Cylinder head nuts torqueing wet or dryt'here has been a discussion about lubing headstud nuts, which is something that I have always done,,but it appears this could be wrong for A series engines--i think I'll keep lubing as previously done all my life, but was wondering what your take is on this
Cheers
willy
I'd imagine Jan would be interested in your opinion
William Revit

Jan
Unless it's just the light playing tricks in the pic of the head that no1 exh valve is lighter in colour than the other three
You mentioned that all the plugs are the same colour,
Plug colour is an indicator of what is happening at the time you pull them out
Valve colour is more of an indicator of what has been happening longer term, the valves take longer to change colour compared to plugs
This is what lead me to believe there is/was something going on there
If no3 inlet is sealing ok then all good there, it may have been caused by no1 exh valve clearance a bit tight------------
William Revit

I top up the dashpots with the damper still in the dashpot but with the cap raised enough to see in and get oil in but keeping the plunger valve (now I know what it's called) below the oil level. You could still overfill but it will find it's own level with use and all things being equal it will hold that level, or sufficient, for a very long time, but obviously you need to check at intervals to make sure.
Nigel Atkins

Plugs in the lovely morning sun, 2 degrees C.


Jan Kruber

The other side
Bare in mind, this is the color after some idling. It is as if no 1 and no 4 with some good will appears a fraction lighter, but they are not fed mainly by the same carburettor, right. 800 rpms.
What I just recalled is, (sorry for the delay) that some time ago the idle had begun to be a little unstable, some times 800, some times 1000 rpms, therefore I did fine tune the mixture. After a period with tuning once in a while, one day I rested one arm on one of the filters and the idle went down. Ahhh.....the manifold bolts were a little loose. I tightened it all and I had an even idle again. It is very , very embarrasing that it happened and I got into the trap.
Now, could the lean mixture during this "loose manifold" prriod have generated so much heat, that the result was discoloration due to overheating? I haven't noticed anything on the temp. gauge.
Could the cyl. head have benn bend now, so that I will have to have it skimmed?
Is it why the oil suddenly recently began to seep out at the roker oil feed?
What about the block, is it engine out, dismantle and have the block skimmed? I hope not, I have plans for some fewer hours in the workshop this winter.......



Jan Kruber

Jan,
take a deep breath, “Don’t panic Mr. Mainwaring” things might not be that bad. It takes a fair bit of overheating to do the cylinder head let alone the block. There’s a known history of gasket issues. And these engines are quite sturdy.

If you can’t settle yourself about the block then put a straight edge on it and shine a small torch along the bottom edge to see if any light gets through – but test the straight edge on a known truly flat surface first as you don’t want any false results.

Don’t worry about overlooking the manifold previously, we all at times have forgotten to check the basics before moving on to the next steps to have to go back, you found it and now you’re wiser.

Checking the colour of the plugs at idle only tells you so much and colours on screens and monitors vary but to me those plugs look fine but I leave the engine stuff to the experts to answer.

Nigel Atkins

Guy,
thank you for the comforting words :-) I feel relieved now.
I have some pictures here, I have rubbed the colored areas with a coarse cleaning spunge with karosene on.
Perhaps the coloration is from the gasket, since I can rub it off.
I have had a straight edge, the back of a wide bladed saw, a handsaw on the gasket surface. I think the saw is very straight, so I allmost trust it.




Jan Kruber

Im on a crossroad until now, I would have assembled the lot earlier today, but postponed it due uncertainity about the head condition.
Guy, you have guided me and when we look at thee theese pictures, with the cleaned head I believe your right, don't you? I will imediately carry on the assembling.
The weather is fine theese days and I would very much like to run it on thuesday, I have a errand with it.


Jan Kruber

Hi Willy, we use engine oil and the appropriate torque to suit the stud spec.
Peter Burgess Tuning

Jan,
just in case you're mixing me up with Guy - I know nothing about engines but if the block and head are both flat and clean then I'd have thought the gasket could be fitted.

(that doesn't account for the valves though of course)
Nigel Atkins

Thoroughly rubbed the gasket surface, like the head, with a coarse cleaning sponge and assembled the lot


Jan Kruber

Sorry Nigel - I made a misteke - hope we can be friends again :-)
But again, to be confused with Guy doesn't sound that offending, Guy seems to be a nice fellow LOL
Jan Kruber

Jan, it was Guy I was thinking got the worst of that mix up.

With time and counseling hopefully all three of us can get passed this. :)
Nigel Atkins

Sorry Jan, and sorry Nigel that wasn't me! I haven't had internet access for a while so only just catching up now. That said, I would agree with Nigel that you probably haven't too much to worry about. It is most unlikely That either the head or the block have warped since you last had them skimmed. These are very robust and forgiving engines.I

The problem does seem to have been mainly to do with oil leakage from the oil feed at the front of the head. My suspicion is that this seal failed because the head was overtightened last time. It is so tempting to set the torque slightly high, thinking that this will improve the seal, whereas in fact it has the opposite effect!

When I asked about the plugs being all the same, what I meant is I assume they are all the same grade of plug?

And one last point, if the carbon build up is slightly oily, then it may just be that the engine is still bedding in after its rebuild last time. Did it have a rebore, or new rings fitted? I thought you had done 5000 miles, but I see it was km, so nearer 3000 miles. The engine is barely run in yet!
GuyW


Well Guy, I do not know why you suddenly became involved, even though the bo-network was available, apparently you are unconscious in my thoughts LOL
To your questions,
I have never overtightened, I'm very cautious when torquening. I never turned it more than 50 ft/lbs.
Today I let it when I hit 48 ft/lbs. The tool was until one / two years ago recalibrated once a year (on my job)
Plugs are of course same grade, the NGK BP6ES.
No rebore, only honing and new pistons and ring off course.
No, actually more than 5000km this year and more than 3000km last year, in all over 8000km = 5000mls.
Funny with the carbon build up, when there's close to non oil consumption. As mentioned earlier, I didn't even refill oil, the oil on the dipstick is only 2 - 3mm lower than when starting out in the spring, Valvoline VR1 Racing 20w50, highly recommended on the American MG Experience forum.
Jan Kruber

Fat fingers and small keyboard buttons.....
should have said: ......"even though no network was available".....
Jan Kruber

This thread was discussed between 31/10/2018 and 04/11/2018

MG Midget and Sprite Technical index

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