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MG Midget and Sprite Technical - 1972 1275 midget producing smoke

Hi All,

I'm new to the forum and would appreciate some help with my midget.

Basically it starts and runs really well. However, if I start and drive t immediately after about 1-2 miles it produces clouds of white smoke, this goes on for about 5 minutes then stops and all is well. If I start the car and let it idle on the drive for 5-10 minutes so it warms up before driving there s no smoke!! I wondered if it might be due to oil pressure with a cold engine.

Any ideas on what is causing the problem and what I should do about it?

look forward to hearing from someone.
Cheers
Ian
I Milton

Does it only happen in cold weather by any chance?

Good to see another local Spridget owner!
Jordan Gibson

Ian.

Firstly Welcome to this BBS and I'm sure in no time you will find many friendly Spridget owners in the North East.

Your smoking problem could be one of several things:

Being a 1972 Model, it should NOT have the 'Smiths' valve fitted on the inlet manifold to control engine breathing, but just in case it has, there is a diaphragm inside there that splits, renewing it may stop the smoking problem.

I fear that it is more likely to be a cracked cylinder head, leaking when the engine is cold and the crack closing up as the engine warms.

Can you determine if it is coolant or oil that is causing the smoke / steam?

The smell is always a good starting point.

If it's coolant it may well be producing steam all the time but you will only notice it when the engine is cold.

If it is a cracked head, don't worry, they can still be found second hand here and there and likely as not, someone on this board may well have one available.

The more I think about this, the more I'm sure it's either a head gasket problem or cracked head.

I would be inclined to remove the head for inspection and take it from there.

If you need any further help or advice, much more will follow on here or you can email me.

Mark.

MG Car Club Tech Rep
Midget and Sprite Club Tech Rep

M T Boldry

Hi,
Thanks for the quick initial responses!!

The problem seems to occur whatever the weather and I am pretty confident that it is oil that is burning. You can smell it in the car, it hangs over the road and the look on the faces of other road users makes it rather embarrassing! I have also been keeping an eye on the water level and am not aware of any continual loss.

Cheers,
Ian
I Milton

In which case Ian, it could be piston rings.... What history of the car/engine do you know?

Mark.
M T Boldry

Ian

I had exactly the same problem which was the oil seperator/breather on the front crank case of the engine. I ended up cleaning it out and disconnecting the closed circuit pipe and fitting a small K&N breather to it. It was always a bit of a mystery but it cured it!

Jody
J Shaw

Hi

Unfortunately I do not know the full history of the engine. I do have a file of receipts for parts that were used during a previous owners rebuild. I will have a look tonight to see if ther is any info about the engine.

I thought that if the piston rings were going the engine would smoke all the time, is that incorrect?

One suggestion a friend of mine made was that the problem might be the valve guides (I may have used the wrong term there you will have to excuse the fact I am on a steep learning curve).

Cheers
Ian
I Milton

I'd just let warm up on the drive before using it, chasing these kind of faults can be very time and money consuming and frustrating too!

The car will let you know soon enough if it's a serious problem, meanwhile make sure you have a recovery service (which you should have anyway!)

All part of the adventure of driving a classic!

AndyB
a borris

Ian,
Burning oil usually produces distinctly blue smoke.
White smoke could be steam, but as you say it is not loosing water it may not be that. Although you could just be seeing condensation from inside the exhaust sytem vapourising as it warms up _ I think that is what Jordan was perhaps hinting at.
White or grey/white smoke could be an over rich mixture which might also then smell oily.

It would be useful at this stage if you can do a compression test as this would identify and isolate head or gasket problems, worn piston rings, or worn valves. If you don't have or cannot borrow a compression tester, they are not too expensive and if you plan to keep the car and fix things yourself, then it is a useful diagnostic tool to own.

Guy
Guy Weller

Mine did this for a couple of years. It may be that, when it's partly warmed up, some of the clearances allow oil to sneak by on the overrun into the combustion chamber. I suspect worn rings or valve stems.

It's not a big problem apart from the smoke; and it doesn't mean you've a fault with the engine that needs immediate attention.

See what happens in warmer weather... or drive a different route (mine always did it from cold going in a particular direction...)

If you disconnect the crancase breather btw you'll have oil coming out of the scroll at the back of the crank.

A

Anthony Cutler

I had lots of smoke out the tailpipe untll I changed the exhaust system to something a lot better. The old one was stailess steel and about 10 years old at least. Pretty badly worn out and had exhaust leaks
S.A. Jones

Well I was going to say worn out valve seals, but the smoke color would most definatly be blue in color...

What about the piston in the carbs getting worn and the dash pot oil is leaking, that would certianly cause the carbs to run rich and hide the oil into the rich burning fuel...giving the smoke a good gray look. plus it would be inermittent.

How often do you put oil in the carbs, via the dashpot? does one carb take more oil then the other?

Prop
Prop***The End in 2012

Ian, this is exactly the same problem I ave with my Midget, start it up all looks fine get 1-2 miles down the road and then time for the james bond special smoke screen.

I to thought and was told when I purchased the car that it was valve stem seals, when I took the old head off I found a broken valve spring so I purchased a head off e-bay and fitted that with new valve stem seals on both inlet and exhaust (wait for the opinions on fitting them to the exhaust!!!)

All looked promising all fitted drive down the road the first time and no problems, I now realise I stood it on the driveway warming up first to make sure I had no leaks before the test drive as I had no screen, next time though queue smoke screen.

I have concluded it must be the piston rings as when I am on a run people following complain of burnt oil and hang back!!! So I am tell end charlie on a run!! How unfair.

So I am now collecting the bits to put a k-series in......

I even tried removing breathers etc but that did not cure it, I suggest checking your oil levels as mine needs topping up frequently

Also do a compression check

HTH Shaun

Part time mechanic/tinkere
Shaun

Here is a possibility: It could be a worn rocker shaft. Oil is pumped to the rocker shaft where it seeps out past the rocker bushes and gets splashed around inside the valve cover, keeping everything nicely lubricated before draining back down the push rod holes to the cam followers. If the shaft is worn then oil will be pushed out faster and gradually build up in the valve cover and after a few minutes running will cover the valve stem seals and increase the leakage down the valve guides.

When you start from cold and warm it gently on tickover, the oil is circulated gently and drainage down the push rod holes can keep up with the supply. As the engine warms, the oil then thins and begins to flow more freely down the pushrod holes, so all is well even when you then set off and start to use higher revs.

If you start the car and set off straight away, the revs are higher, pump pressure is higher and so is the flow into the valve cover, but the oil is still cold and won't flow away down the pushrod holes fast enough. After a few minutes like this the level builds up until it covers the stem seals, leaks past them and produces a smoke screen. As the oil warms up it flows more freely and the problem then cures itself.

Take the rocker cover off, turn the engine so that a tappet is off-cam and feel for any vertical slack in the rocker. Wear will be on the underside of the shaft which may have developed ridges that you can feel with a finger nail. Replacement rocker shafts are not expensive and it may be sufficient to replace just the shaft and re-use the same rockers.

All just theory, but it would explain your symptoms I have had that exact thing happen on an A series engine before.

Guy
Guy Weller

WOW GUY!!!

I got to remember that one, did this happen to you, I know I would have never made that connection....

I wonder, would there be hasitation and power problems also?

Im impressed
prop
Prop***The End in 2012

Many thanks for the many suggestions. I ordered a compression gauge yesterday and will look into how the individual cylinders are performing and report back. I was hoping to take the car out this morning to check the colour of the smoke, however despite overnight temperatures of +4oC the council have salted the roads! so that will have to wait.

I was thinking about the problem last night and remembered that the previous owner told me that when he bought the car it was "full" of oil, way over the top dipstick level. He had drained and changed the oil. I don't know why I didn't think of this earlier. Could an overfill have put oil somewhere it shouldn't be and cause the described problem.

Last summer when my wife took the midget and I followed behind there was very little smell of ongoing oil burning and nothing obviously coming out the exhaust.

Since I have owned the car it has done only a very low mileage (very wet summers!!) and so am not sure as to how often one should refill the carb dash pots.

I can tell this is going to be fun trying to chase the fault down!!

Cheers,
Ian
I Milton

Prop - Yes it did. My explanation is long and laboured, but the symptoms were the smoking for a few minutes not long after setting off - unless I let it idle to warm up first.
I discovered what was going on when I took the rocker box cover off and ran it from cold. When I revved the engine oil pissed out from under the rocker bushes and the oil level on top of the engine was building up a lot faster than it was draining away. Replacing the rocker shaft on mine cured the problem.

Guy
Sorry to keep referring to rockers - but I am sure you know I am not talking about the bits under the doors!! though!
Guy Weller

Rocker bushes and shafts are an ofetn missed item when looking at engine problems and can be the cause of many....

Guy's explaination makes a lot os sense and is a very easy one to overcome....

Mark.
M T Boldry

My 'smoke for 30 secs 5 mins into a run' with the A series was fixed by a rebore... old rings were worn and one was split... but I must stress I rebuilt the engine cos I wanted more cc's and a different cam. Compression was fine. Otherwise would still be smoking.

Excess oil can lead to smoke - the crank acts like a food mixer in the sump and whips the oil into an emulsion that flies around everywhere incl onto the bores. Worn rings esp won't cope with this, and more than the usual will sneak by.

A
Anthony Cutler

Hey milton,

Just another thought, would be to check the engine with a vaccume gauge, Ive only looked into this dignostic tool in the last 6 months after hearing about it 3 years ago, the info that is gained is substaincial,(about 12-15 differant things) you want to use a reg. vacume gauge NOT a automotive one for the dash...it needs to read ALL 30 notches not 1 notches equal 4...then look on the net for what the various readings mean...google auto diagnostics and vacume gauge, theres like 60+ sites with this info

you can buy a vacume gauge at any hardware store...$10 - $15 dollars, buy some extra fittings and stick it into one of the vac ports on the intake manifold

the reason for not an automotive vac gauge, is its designed to not bounce around the needle and takes some of the play out of the gauge...which is needed for accurate readings.

prop

Prop***The End in 2012


I have exactly this problem with a 1973 1275cc Midget. It has done 6000 miles on a recon engine and the problem has started to occur in the last 1500 miles or so.

The smoking occurs after driving for about 1 mile and is accompanied by a rattling/pinking - sounds like the oil pushing past the pistons? After about five minutes the problem disappears.

The car runs at 80 psi dropping to about 70 when hot.
This seems high and my first thought is to replace the oil pressure relief valve. Any thoughts appreciated.
I D Wadddell

Probably not helpful, unless you can test it, but high readings like that could possibly just be a faulty gauge.

Guy
Guy Weller

This thread was discussed between 10/03/2009 and 18/08/2010

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