Charles Durning's Journal --
A Different PCV System for MGB with a Smiths Valve I’ve had a perplexing oil consumption issue with my MGB GT. The engine seems to be in good shape with good compression, the current Smiths PCV system produces a commanding negative pressure in the crankcase, the spark plugs are clean, and no excessive external oil leaks. In researching the issue, a general opinion is a problem with the vapor separator in the front tappet cover. Apparently those can become clogged with guck and will no longer allow the oil vapor to drop out of suspension as it passes through the PCV system. The vapor separator can be cleaned using all sorts of “snake oil” or oven cleaners. In fact those appear to work well in cleaning the guck. But, for some reason I’m thinking that may not be a solution for the oil consumption problem. In inspecting the PVC system on the GT I noticed an accumulation of oil in the Smiths PCV valve. Also there was a lot of oil residue in the hose leading from the tappet cover to the PCV valve. It’s apparent that oil is getting past the vapor separator in the tappet cover. That may not be the only source of oil consumption, but, it’s worth investigating. Part of the problem could be the airflow through the PCV system. That can be demonstrated by the commanding negative pressure in the crankcase. Perhaps the air flow through the PCV system is too fast to allow the oil vapor to drop out of suspension in the vapor separator. To experiment, I put a restrictor in the hose between the between the vapor separator and the Smiths valve. Not sure if that had any effect on the oil consumption since there is still an accumulation of oil in the PCV valve. Perhaps slowing the air flow at the vapor separator will allow enough time for the oil to drop out if suspension or adding an oil catch can solve the problem. Though the catch can could minimize the amount of oil passing through the system it also has its drawbacks. The oil that does drop out of suspension is then stored in the can. Somehow that doesn’t seem like a solution. In looking at an engine I had in the shop I got to thinking, why not add another vapor separator in parallel to the original? There would be the same flow through the system, but, the airflow would be split between two vapor separators. That could slow the inflow down enough to allow the oil vapor time to drop out before moving on to the PCV valve. According to Bernoulli's principle this should work. Now that has possibilities. So how can that be executed? The MGB engine has 2 tappet openings on the side of the block. Why not add a second vapor separator to the rear tappet opening? All it would take is modifying the rear vapor separator with a longer pipe to join up with the front vapor separator at the front of the engine. Then “T” the two together and route to the PCV valve. Well not so fast. The rear vapor separator sticks out enough to keep the exhaust manifold from sealing properly on the head of the engine. Clearly the rear separator needs to be modified for clearance. The modification is simple enough. Just cut away the offending area and then weld in a patch piece. That gave enough clearance so the exhaust manifold can be mounted. After that was done, the tube on the rear separator was cut and then extended to the front of the engine. All that’s left is to make a “T” fitting to join the 2 vapor separators together. In theory this should work. I’ll see once I’ve lived with the system for a while. If this works well I will apply the same solution to the PCV system on the Morris.
Posted 2020-05-19 07:21:48 by charles durning
A Different PCV System for MGB with a Smiths Valve I’ve had a perplexing oil consumption issue with my MGB GT. The engine seems to be in good shape with good compression, the current Smiths PCV system produces a commanding negative pressure in the crankcase, the spark plugs are clean, and no excessive external oil leaks. In researching the issue, a general opinion is a problem with the vapor separator in the front tappet cover. Apparently those can become clogged with guck and will no longer allow the oil vapor to drop out of suspension as it passes through the PCV system. The vapor separator can be cleaned using all sorts of “snake oil” or oven cleaners. In fact those appear to work well in cleaning the guck. But, for some reason I’m thinking that may not be a solution for the oil consumption problem. In inspecting the PVC system on the GT I noticed an accumulation of oil in the Smiths PCV valve. Also there was a lot of oil residue in the hose leading from the tappet cover to the PCV valve. It’s apparent that oil is getting past the vapor separator in the tappet cover. That may not be the only source of oil consumption, but, it’s worth investigating. Part of the problem could be the airflow through the PCV system. That can be demonstrated by the commanding negative pressure in the crankcase. Perhaps the air flow through the PCV system is too fast to allow the oil vapor to drop out of suspension in the vapor separator. To experiment, I put a restrictor in the hose between the between the vapor separator and the Smiths valve. Not sure if that had any effect on the oil consumption since there is still an accumulation of oil in the PCV valve. Perhaps slowing the air flow at the vapor separator will allow enough time for the oil to drop out if suspension or adding an oil catch can solve the problem. Though the catch can could minimize the amount of oil passing through the system it also has its drawbacks. The oil that does drop out of suspension is then stored in the can. Somehow that doesn’t seem like a solution. In looking at an engine I had in the shop I got to thinking, why not add another vapor separator in parallel to the original? There would be the same flow through the system, but, the airflow would be split between two vapor separators. That could slow the inflow down enough to allow the oil vapor time to drop out before moving on to the PCV valve. According to Bernoulli's principle this should work. Now that has possibilities. So how can that be executed? The MGB engine has 2 tappet openings on the side of the block. Why not add a second vapor separator to the rear tappet opening? All it would take is modifying the rear vapor separator with a longer pipe to join up with the front vapor separator at the front of the engine. Then “T” the two together and route to the PCV valve. Well not so fast. The rear vapor separator sticks out enough to keep the exhaust manifold from sealing properly on the head of the engine. Clearly the rear separator needs to be modified for clearance. The modification is simple enough. Just cut away the offending area and then weld in a patch piece. That gave enough clearance so the exhaust manifold can be mounted. After that was done, the tube on the rear separator was cut and then extended to the front of the engine. All that’s left is to make a “T” fitting to join the 2 vapor separators together. In theory this should work. I’ll see once I’ve lived with the system for a while. If this works well I will apply the same solution to the PCV system on the Morris.
Posted 2020-05-19 07:21:48 by charles durning
