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MG MGB Technical - Crankcase ventilation etc.

My 1970 18Gh engine is set up with a Euro spec distributor and 1 3/4 SU carbs. I have an aluminum valve cover with a vented oil filler cap. The crankcase is vented through a tube to the atmosphere. Gas tank is also of earlier vented type. There is no Charcoal canister. All these modifications made by PO. Should I be concerned about not using the charcoal canister and venting the crankcase to the atmosphere?
Greg Bowman

Greg. I would be concerned about venting the crankcase to the atmosphere. These were known as "road draft" systems, where you simply had a line hanging down into the slip stream and the air blowing across the bottom of the open tube (hard metal tubes, they were) would creat a slight vacuum and remove fumes. That system was always known for blowing out a little oil when the engine was pressed hard. The hooking of the vent line to the carbs or air cleaners seems to work better for me.

As to the charcoal canister. It was a means of trapping fuel vapor and sucking it back to the fuel tank through the hard line running from the tank to the canister and functioning as the fuel tank vent. I am not sure exactly what year the sealed system was started. I do not have it on my 68. If you should have a charcoal cansister, there should be a line or nipple near the fuel filler opening in the gas tank, upper side. Make sure this is capped off properly so you do not get a fuel vapor build up in the trunk. Les
Les Bengtson

If your engine serial number begins with 18GH not 18GJ then your car never had the carbon canister or the sealed gas tank installed from the factory. For 1970 only the CA cars had this installed. The serial range for this was the 18GJ series engines. As original the crankcase ventilation was sent to both carbs from the vent tube on the tappet cover. It was changed when the non stock HS-6 carbs were installed. The original HS-4 carbs had a small tube which connected to the venturies. Unless you have made other changes (overbore, headwork, headers etc) I would guess that the HS-6 carbs will be too much carb for a stock engine.

HTH

Ron
(70 18GH B)
Ron Smith

So, should I just drill a hole in the back of one of my K&N filter covers and run the tube from the crankcase there? BTW Ron, there have been some other modifications with exhaust, etc. It runs very well. I'm just primarily concerned with running the crankcase vent as it is now.
Greg Bowman

Greg. You might take a look at the system used on the 68 models. It might adapt to your needs. It involves the line from the front tappet cover going to the intake manifold with a "mushroom" valve moderating the vacuum. Do you have a copy of "Original MGB"? I believe it shows a picture of the system. If not, check out the Moss catalog. Les
Les Bengtson

It would really depend on what type of manifold that was installed. The Clausager original MGB book shows many if not all of the types used. The mushroom style that Les speaks of was used on the MKI cars, and the manifold would have a 1/2" or there abouts threaded hole about dead center between the carbs. The later style MKII 68 to 72 had a line from the front tappet cover going to a Y then one each to both carbs. My MGC which has the HS-6 carbs has the line going to the airfilter box (one piece) I would perhaps try to run a line like the original, that is a Y running to both airfilters rather than all into one.

Safety Fast

Ron
Ron Smith

Les has go it spot on. I have been running my '73 B for about 12 years using the tube from the front tappet cover to go to a standard Smiths PCV (looks like a funnel but covered on top). The bottom of the PCV attached to the intake manifold.

In my case, I still have my original valve cove with the orificed tube at the rear. I have attached a small round K&N filter to this tube. I have a sealed oil filler cap. This setup allows the intake manifold to draw a slight vacuum through the crankcase and keep it ventilated.

The benefits to this are a) positive ventilation and a slightly negative pressured crankcase. The slight negative pressure on the crankcase helps to keep the engine bay clean.
Richard Smith

There is a plug bolt on the HS6 manifold near the front carb. Will the PCV valve thread in there? BTW, thanks everyone for all the help. I'm still new to these wonderful cars.
Greg Bowman

Ok I looked again and found that the HS6 carbs have the fittings to run the crankcase vent to a Y and then to the carbs. They were just plugged.Is there any reason not to run the crankcase vent this way as opposed to a PCV valve?
Greg Bowman

Greg,
That is my prefered vent system. One less thing to go wrong. I would connect the air make-up hose (from the valve cover) to a fitting that draws air from the carb side of the air cleaners. The stand alone K&N filter is fine, just one more item to service.
Leland Bradley

I have a 77 b i would like to lower the front using the front cross member out of a 71 b using the 71 steering rack what kind of problems am i going to have hooking the steering rach bach up to the universal joint. thank you
bill walton

This thread was discussed between 18/07/2002 and 21/07/2002

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