Burning oil in an MGB or Midget? It may not be as bad as you think!

There are two faults which show up in the breather systems of Midgets and MGBs which cause dramatic oil consumption and lots of blue smoke, even with a reconditioned engine.  Quite a number of engines have been unnecessarily reconditioned because of these faults so if you have a smoky engine, although the odds are that it does need overhaul, check these out before you dive in and spend lots of money:

First miracle cure:

The breather pollution control valve on the manifold, where fitted, (approx 1964 to 1969-70 – 18GA, 18GB, 18GD MGB engines, 10CC, 12CC and early 12CE Midget engines) can develop a leak which allows the crank case to be significantly vented to the inlet manifold under high 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.

Warning:  While it is tempting and much cheaper to simply vent the breather to atmosphere, doing so makes the engine more likely to leak oil – particularly if it is an A series Midget or 3 bearing MGB.  The reason for this is that in its operation the breather maintains a small partial vacuum in the crankcase, which works against oil getting pushed out of the seals (or the rear scroll in the case of the 3 brg B & A series). Venting to atmosphere achieves the reverse effect – it maintains a small residual pressure inside the crankcase (it won’t be much, but without any pressure difference at all there would be no outward flow through the breather).

The partial vacuum system is used by all cars now and is one of the reasons modern engines don’t leak oil.

The other miracle cure:

The breather oil separator on the engine can become blocked, in which case simply cleaning it out solves the oil consumption problem.

This unit is incorporated in the front pushrod cover on MGB’s, while on 1275 Midgets it is attached to the timing chain cover.  (Sorry, the 10CC engine’s arrangement has slipped my memory at the moment but it will be one or the other of these two).

There were two versions of the pushrod cover separator, the early one had a row of small-ish holes along the botom of the inside face while the later one had a much larger hole about 1.5 – 2″ square-ish at the rear end of this face.

It is the small hole version of the pushrod cover separator which is most prone to blocking up.

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.”

A simple way to address the gunge is to get an engine reconditioner to put in the cleaning tank.

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