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MG Midget and Sprite Technical - Blue exhaust smoke


I am new here so please be gentle!

bought my midget a couple of months ago. it has been running mostly fine.

But today i have large clouds of blue smoke while idling.

i understand this will be oil, but how do i go about finding where the fault is?

I am not the most gifted of mechanics but eager to learn any help is much appreciated.

many trhanks


P J Gingell

Hi Pete

Well the good news is that if the blue smoke has suddnly just happened hen chances are the problem is not terminal. Had it been there all the time then potentially that could be a different matter

OK if has just occured what type of Midget do you have.

First thing is have you over filled it with oil?

Or have you had it jack up for a while and started it whilst it has been jacked this can cause oil to be sucked out of the breather straight into the engine.
Robert (Bob) Midget Turbo

Or if it is a mk2 or early 1275, the breather valve can malfunction giving exactly what's described.

And yes, over filling with oil can be dramatic. One of the boys recently put a little too much in during an oil change. Fine on ther road, but in an autotest it caused an alarming smokescreen! Drained off half a litre and problem gone.
Paul Walbran


thanks for quick response.

it is a late 1275 midget.

it's not been over filled with oil or been jacked up.

it must have lost nearly all its oil yesterday and at no point stopped smoking while at idle my friend in the car behind bears witness to that.

i'm glad to hear it may not be terminal yet.

what should i be looking at next?

P J Gingell

Blue smoke can be produced for a while e.g. when laying oil is sucked out of the crankcase breather.

But it should stop after a few mins.

Continuous large amounts of the blue stuff (I assume out of the exhuast pipe) has to come from the combustion chamber. It's got there either through the inlet - sucked in with the fuel/air, or down the valve guides - or past the rings / piston, or from a leak in the head gasket.

My suggestion would be to try a compression test as next step; all 4 cyls should read the same; 120-160 psi is typical value. If one is lower than others, this suggests ring, gasket or valve guide problem.


Anthony Cutler

Even on the late 1275's the breather could be an issue. I have never struck it with a Midget, but certainly with the equivalent system on the B. I had a customer who reported excessive gunge in the gauze of the breather canister promoted lots of blue smoke. It was solved by putting the canister assembly in a reconditioner's cleaning tank overnight. But not before the engine had been reconditioned in a fruitless attempt to stop the smoke ...
Paul Walbran


thanks for the help so far.

compression tests done: all at 50 psi except cylinder 2 which barely moved the dial. i don't know how accurate the compression tester was so don't know if all the cylinders are way down by exactly the same amount or the tool is off. but cylinder 2 was definitely bad.

head off and valves on 2 look badly worn, seat on the exhaust looks less than perfect too.

i think the other valves look ok.

any suggestions on where to go from here? i think i need to find a friendly machinest to sort the seats out; is it worth thinking about uprating the cylinder head or would this be throwing good money after bad?


P J Gingell

Wow...50 psi on 1,3, and 4 and nothing on 2.... certianly a testament that these little engine just keep on running no matter what

So the head is off....peter burguss is running a really good special for rebuilding heads....that would be the 1st call id make.....i want to say 200 gbp give or take.

You wont find much better in the biz

The 50 a little iffy, im not sure what to think...might be time for a purely guessing new rings and maybe bearings at the least...

Im looking forward to what the others say

Payne gaskets (BK 450) is your friend


Id check the compression tester on a known good car and another known good compression tester to give a better idea if the xurrent tester is okay....that way you would have a better idea if the compression is realy 50 psi or not

This thread was discussed between 14/04/2011 and 22/04/2011

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