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MG MGB Technical - Crankcase ventilation

I have a 74 BGT that has been desmoged and the carbs changed to a weber down draft by the PO. I am having oil blown from the front lifter inspection cover into the air filter, saturating it and running down the carb. The valve cover is still connected to the charcoal canister. I am apparently experincing excesive pressure build up in the engine. The engine had been rebuilt prior to my aquisition. Any thoughts
Scott Shirk

On the driver's side of the engine near the front shouldbe a small pipe coming out of the engine. A hose should be connected to it and run to a vacuum port on the bottom of the air filter of the carb. What type of air filter is on your Weber?
william fox

There's supposed to be a heavy wire mesh in that cover which traps the bulk of the oil. If it's missing, then I suppose you could get some oil coming up the pipe.

Otherwise, checked your compression lately? May be a case of way too much blow-by pressurizing the case.
Matt Kulka

I will just chime in with Matt. If you also have a bad oil leak out the front and/or rear crank seals, then indeed you may be suffering from blow by, usually indicating worn or improperly fitting rings.

Check the compression, and then run the engine and take off the oil filler cap. Place a piece of oridinary paper about the size of a playing card over the filler hole while the engine is running. If that piece of paper gets blown away from the filler neck, you have bad blow by. If however, it gets sucked to the neck and held there, then your carbs are sucking hard on the crankcase breather. If you have a PCV valve and it is operating correctly, the piece of paper "should" just vibrate over the hole as the engine runs.

One thing to consider if the wire stuffing has been lost out of the tappet cover with the breather connection: Use a Coarse stainless wire wool to replace it. I would recommend using one of those stainless curly choregirl pads as the stainless in those is not brittle like the more ordinary steel wool and much less likely to disintegrate on you and find its way into places it doesn't belong. FWIW
Bob Muenchausen

Connecting the PCV hose to the bottom of the air filter, in my experience, does not work. This connection is OK to draw filterted air into the crankcase via the draw tube on the valve cover found on the later 18V engines (normaly connected to the evap. cannister. The connection on the air filter is not really a port and will not work properly to draw crankcase ventilation into the engine. It may draw oil laden vapor that results in oil smoke from the exhaust.
There may be a PCV port at the base of the Weber carb, just after the throttle butterfly. I had a Weber on a 73B about 10 years ago and I do not recall that there was such a port, but my memories are getting a bit dim. I did resort to using the mushroom style PCV as found on the pre-68 engines mounted on the Pierce manifold, where it is tapped for a brake booster vaccuum takeoff, to obtain what I felt was proper ventilation.
Andrew Blackley

This thread was discussed on 25/06/2002

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