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There are two faults which show up in pre 1972 MGB’s which cause dramatic oil consumption and lots of blue smoke, even with a reconditioned engine:
First miracle cure:
The pollution control valve on the manifold (where fitted - 18GA, 18GB, 18GD engines) can develop a leak which allows the crank case to be vented to the inlet manifold under vacuum rather than only under full-ish throttle conditions when the manifold pressure is much closer to
atmospheric. The result is that the strong vacuum sucks furiously at the crankcase,
scavenging neat oil as well as the intended fumes into the inlet system. Hence oil combustion and blue smoke!
The valve is readily identifiable: It is attached to the middle of the inlet manifold and has a flat circular top of about 3” diameter. A hose joins the outlet (points towards the front of the car) to the breather on the side of the block.
To confirm the diagnosis: remove the PCV valve but leave the hose which joined it to the manifold in place. Block this hole off with a suitable bolt or whatever, and road test to see if the problem has gone.
Many an engine has been needlessly overhauled because of failure to check this out!
Replacing the diaphragm or if necessary the whole valve (depending on the nature of the fault) will fix the problem in 10 minutes.
The other miracle cure: as described by Robert Paterson:
Well, I've found the answer at last! Last week I took off the "side cover with separator" and it was just as you said, with small holes along the bottom. I could blow through it ok, so it was not blocked.
I decided to drill out the holes to a bigger size. When doing this, I found that it was full of very black goo! In fact, it took me three days to remove the goo - 37 years of old thick solid oil.
I fitted it back on the car and off we went with no problems - no more blue smoke! In fact, the motor seems to be a lot better and more alive, if you know what I mean.
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