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MG MGB Technical - WEEPING VALVE COVER

Hello, have not written in a year. 1975 B installed reman .40 over engine with peco header & 38mm weber
carb. Blew oil thru valve cap-tried vent tube loose,
v/tube into exhaust, smiths pcv valve, cutting rear v/cover elbow...found all top rings cracked, 1 piston skirt broke in hand & rods installed backwards not oiling dist. side of engine. New pistons, rings, rod
bearings, head studs, honed cylinders. Slight oil thru cap for 2,500 miles now pushing large amount out again. Aluminum valve cover with TINY hole drilled in right rear to breathe. non vented cap, tappet line to base of weber. dry compression 180 180 150 150. Wet test brought last 2 cylinders to 160. Hate to think I have to pull the head/engine again. Any suggestions to better decrease crank pressure? From the get-go pressure was not a problem with the stromberg-only with the Weber installed. I do not have excessive oil in my air cleaner, just oil pushing throught the cap & a small amount thru my breather hole. Appreciate any
help, also car runs strong & has zero driveability issues. Regards, Nestor
D Caryk

If you are saying you have a non-vented oil filler cap and oil is leaking from it then it isn't sealing to the neck of the rocker cover. With an aluminium rocker cover this could be because of a mis-match between cover and cap, but then I get a bit of weeping from my cap with a proper rocker cover, which I cope with by tying a 'neckerchief' round the neck of the filler tube. I'm not surprised you have a small amount of oil seeping from the drilled breather hole, but you should be using a vented filler cap and no breather hole. If crankcase pressurisation were bad I'd expect to see loads pumping out of that hole. Do you really have crankcase pressurisation? Have you removed the oil filler cap and held a piece of paper over the hole? What is on the 'other end' of the crankcase ventilation system? Is the front tappet chest cover/front cover port piped to a vent on the carb? A PCV valve on the inlet manifold? The air filter case? Via a filter to atmosphere? Or just blocked off? Ideally you should have positive ventilation from a carb port, or progressively less ideal from a PCV valve, the air filter, via a filter to the atmosphere, or blocked off altogether the worst of all. Webers don't seem to have the ventilation port whereas Strombergs and SUs do. Whilst the non-positive ventilation from anything other than a carb port or a PCV valve probably isn't contributing to the oil blow, it isn't giving best ventilation either.
Paul Hunt 2

Paul, thanks for your response. I see your name here frequently & respect your & other opinions. I
have my tappet line to the base of the Weber carb with no oil build up present. I had read a thread of yours earlier regarding the paper test & just popped my plugs back in & found that the paper flutters-as I suspect it should-over the filler neck. This may indicate a normal crank pressure situation & point back to the bottom end. However for tonights 45 mile ride home I plan to tighten the filler cap with an additional gasket of original design. Thanks for
your help, Nestor
D Caryk

This thread was discussed on 23/02/2006

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