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MG MGB Technical - Rocker cover breathing on '69 mgb

Hiya folks! Just a quick one for yous - due to only doing short daily journeys I'm finding white emulsion inside the rocker cover (no, head gasket is fine) so having cleaned it all out, I've enlarged the breathing hole in the oil filler/breather cap as an attempt to allow better water vapour evaporation. Was this the right thing to do? Cheers, Rich
r j symons

69 models had the new carb ventilation system, taking over from the previous PCV valve on the inlet manifold. Both use forced ventilation, and shouldn't suffer from internal condensation, unless perhaps your journeys are so short that the engine never gets up to temperature. In which case you should look for a longer way home, at least.

You can check whether the ventilation system is functioning, by removing the oil filler cap while idling, and it should increase the idle speed slightly - with carb ventilation at least. If it doesn't - and it perhaps may not if you have removed the restriction in the oil filler cap, then you should be able to feel slight suction if you place the palm of your hand, or a sheet of card, over the oil filler hole, which should lower the idle speed. If that doesn't happen then you need to check the vacuum path is clear - from the carbs in that case, or through the PCV valve otherwise.

Increasing the oil filler cap hole will adversely affect the mixture, both at idle and through the rev range.
paulh4

Rich,

If the breathing system on your car is functioning properly the inside of the engine should be under a slight vacuum so the air goes IN the hole on the filler cap, making the hole slightly bigger will not make a huge difference.

The main extraction of water vapour is via the carbs / manifold.

Is the breather system clear and doing its job? You should be able to feel a slight sucking on your hand if you place it over the open rocker neck with the engine running.

The white emulsion is just the additives in the oil doing their job of holding excess water in suspension.

Constant cold running is not good for engines, they need to get right up to temperature for at least 30 mins to boil off the water.
Chris at Octarine Services

Thanks to you both for your answers! I shall go and have a quick try. Many thanks again, Rich
r j symons

Take the front valve chest cover off and soak it in petrol to clear out any congealed emulsion from the internal mesh.
Allan Reeling

Had the ame issue on my 1964 MkI. Proved to be a hairline crack in the cylinder head allowing coolant to seep into the oil.

Gave me the perfect excuse for a P Burgess Econotune head.

Regards

Jan
Jan Emil Kristoffersen

I had the same issue as Jan, I thought it was condensation until I took it to Peter Burgess. before he'd accept the head he had the top cleaned up with a small grinder and found a hairline crack. I hadn't noticed any water loss but it must have been just enough to cause the problem.

As allen says the mesh in the breather can get blocked, I tried soaking it to no avail, eventually I cut the back open and removed the mesh, I was the able to un tease the mesh, wash it out and put it back. I then welded the cover back closed.
R.A Davis

This thread was discussed between 12/03/2017 and 13/03/2017

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