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MG Midget and Sprite Technical - Crankcase ventalation

I have 948 Bugeye which has always leaked some oil from the back crankcase seal. How ever recently the leak has increased somewhat. The only thing that has changed is recently I have taken off theold factory type air filters and fitted Ram tubes,with the result that there is no conection for the vent pipe to thetop of the rocker cover. I suspect that this has resulted a increase in crankcase pressure,thefore more oil getting past the seal.
My question is can I conect the vent pipe onto vacuum fitting on the inlet manifold as on the later 1275 engine cars? (my 948 still has vent pipe in the tappet cover so is not a closed system)
Noel Copping

No too much vacuum from a direct connection to the inlet manifold. You will have to use the 'mushroom' PCV valve t make that connection.

Or, if you can get and jet them correctly, the later twin su's, and the y piece connection to the tappet cover should work.

And yes, disconnecting the original setup is the cause of your leak.
Lawrence Slater

I should more accurately say, the cause of the *increase* in oil leaking is because you've disconnected the vent system. The cause is crankcase pressure not being relieved sufficiently in the 1st place, perhaps due to excessive blowby, or maybe because the original crankcase ventilation via the air filters wasn't good enough anyway.
Lawrence Slater

Thanks Lawrence
Blowby shouldn't be a problem as it is afully rebuit motor,has done about 3000mls.It is fitted with Hs2 carbs so I should able to fit the Y pipe as on my MK 4 sprite. Should I also use a vented oil filler cap?
Noel Copping

Ah well then you're quids in. Even with a new engine there's some blowby. But as long as you have PCV, it doesn't cause a problem. (There's a long story to that though, that as you have tappet covers, you don't need to know, and everybody else is completely fed up with hearing about).

Yup, use the standard plastic vented cap. The small hole in the underside, allows just anough air *IN*, not to weaken the mixture too much, as the air is drawn down through the engine, and out through the breather(tappet or timing chain cover), relieving the pressure and carrying with it the gasses that degrade the oil.

If you still have a problem after that. If you swap to an electric fuel pump, you can fit an additional -- or move the breather, to the mechanical fuel pump blank.

But I don't think you'll need to.

One thing though. Are you sure the rear scroll is doing it's job properly? What condition was the 'eyebrow' in when the engine was in pieces? And, as I was reminded not so long ago, the eyebrow cap over the crank is not supposed to be removed, as it's line bored when fitted to the block. Hence if it is removed, it MUST be put back in exactly the correct postion. I took mine off on both my engines, but I've always made sure it tried to fit it back in the same position. I aim for as close as possible, but not touching the crank. Seems to work ok.
Lawrence Slater

There is no vacuum applied to the rocker cover on the Frogeye in the standard setup, rather it occurs at the draft tube connected to the tappet side chest covers.
The pipe between the front air filter and the rocker cover allows fresh clean air to be drawn in to the engine.

If all you have done is to remove this pipe and you haven't blocked it off then the cause of your increased oil loss is elsewhere.

If, on the other hand, you have blocked off the rocker cover vent that's definitely not going to help with your oil loss problem.

SA Wood

Good point Simon. I hadn't read the 1st post properly, and registered that it's the early draught tube ventilation.

Lawrence Slater

This thread was discussed between 26/07/2015 and 27/07/2015

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