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MG MGB Technical - Blue exhaust smoke

I have a 1973 MGB GT left hand drive that runs good. But I have noticed a blue smoke. What can you recommend me to do to see what the problem is, if I have to get a new cylinder head or if the problem lies with the piston rings. Is there a simple solution to find it out?
GA Arnason

Blue smoke is likely oil burning. To confirm, what is your oil top up rate? Could be due to worn rings or bores, or sloppy intake valve guides. Do a compression test with dry bores and then with about 3 squirts of engine oil in the cylinders. Also check the gas rate out of the filler cap.
Art Pearse

It is also due to a choked front tappet chest cover - check for oil in the breather pipes.
Chris at Octarine Services

Not sure I understand your reasoning, Chris, unless you mean excessive pressure in the crankcase is pushing oil past the rings into the combustion chamber. I'd have said an *unblocked* front tappet chest cover and hoses could have excessive oil being pushed through them into the carbs before being burnt. Easy enough to check, seal off that hose (both ends) and if the blue smoke stops, and there is oil in the hoses, then that is the culprit, possibly blowby from worn rings/bores, but these breathers are known to pass excessive oil under some circumstances, not always clear why.

If you only get it when blipping the throttle after idling a while, or accelerating after a long downhill run on the overrun (can you do that in Iceland?) then it is more likely to be valve stems/guides/seals.
Paul Hunt 2010

Thanks guy's for the quick responces. The first thing I'll do is to drive downhill. Another question, a bit silly.... Where are the breather pipes you mentioned Chris?
GA Arnason

From the front tappet chest (right-hand side looking in from the front) going to a Y-pipe and then to angled ports on each carb.
Paul Hunt 2010

Paul,

The mesh in the front chest cover is designed to catch the oil mist in the air that travels from the crankcase to the carbs. If it is in good condition then the oil returns to the sump in liquid form and only air & fumes go into the carbs.

If it is choked with carbon deposits the oil travels up the mesh because of the reduced air passages and faster air speed - gravity doesn't get a chance to return it to the sump.

If it is missing then the oil mist goes straight to the carbs.

There is always some blow by and the mesh is designed to cope with that - even the blow by from a worn engine or one with broken rings shouldn't overwhelm the mesh. Then you get oil burning from oil getting past the rings or down the valve guides.

In any case of oil burning I always look in the breather tubes first.
Chris at Octarine Services

GA-
If the engine smokes under hard acceleration, then the problem most likely lies with the rings. If the engine smokes when downshifting to high RPMs with a closed throttle, then the problem most likely lies with the intake valve guides.
Stephen Strange

Ah, *mesh* choked yes, but not the cover per se.
Paul Hunt 2010

This thread was discussed between 17/03/2010 and 20/03/2010

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