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MG MGA - Another 1800 question / Breathing?

I am finshing up my MGB 1800 engine swap in my MGA. My question is how should the engine breath? My original 1500 had a down spout tube that came out of the side of the engine and tuned down towards the ground. It then had a vent pipe comng out of the tappet / valve cover that plugged into the air cleaner assembly on the carbs.

The 1800, (1968 5 main bearing), engine has the vent tube coming from the side tappet lifter cover and turns upward. It does NOT have the vent tube on the valve cover.

How should I set up the brreathing for this engine?

Thanks in advance,
Danny
Danny T

Danny

I connected the tappet vent and rocker box vent together by a T piece and then to the front air cleaner. 5th picture down: http://freespace.virgin.net/stephen.gyles/odds_and_sods.htm

Steve
Steve Gyles

Correction. 6th picture down!

Steve
Steve Gyles

Danny. If you are using the original (18GF) rocker arm cover, it has a vented cap. That is your air input source. The 18GF used a line from the front tappet cover to the "mushroom" PCV valve on the intake manifold. Other options are the one that Steve uses, hooking up to the air filter, or, the later HS-4 carbs had a connection for the tube from the tappet cover--line to tappet cover, Y connection, line to each carb.

Any of these systems would work better than the old road draft tube system. Work with what you have available to you and what seems to look the best to you.

Les
Les Bengtson

Les is right recycling all blow by with a pcv is best A tee like Steve reccommended also works well and is very simple. Using the original A valve cover, air filter and tappet cover/downdraft tube works also.
R J Brown

On my 18V, I have fitted an extension hose from the tappet downdraft tube (I'm using an original down-pointing tappet cover)that extends to about 5 in.above the ground. Also have a 1/2-in. hose barb in the side of the alloy valve cover with a hose that extends to just above the ground. Good engine breathing, but both drip a little (the only engine leaks I have). Is there a way to improve this?
thanks,
Tyler
Tyler

Tyler. The "downdraft tube" or "road draft tube" is an inefficient form of vent for the crankcase. The US cars used it until about 1968 when they were required by federal law to have a closed breather system. The Brits had switched over to more efficient systems long before.

Your current system has two "vacuum" sources and no source of incoming air to balance the vacuum. This could lead to excessive oil use were the road draft tubes an efficient source of vacuum.

The elbow on the top of the 18V engine was used as the air input source and had a line running to the charcoal cannister as the system was originally intended. Install some form of small air filter on it and use it as an input source.

The front tappet chest can be hooked up in any of the three ways I suggested and will provide a positive crankcase ventilation system that works properly.

I once tried the road draft tube many years ago. Had been suggested by the fellow who sold me the Weber conversion kit for my car. It leaked oil from the draft tube. Replacing the draft tube with a rubber hose connecting the air filter to the tappet cover worked well and no more drips.

Les
Les Bengtson

This thread was discussed between 26/03/2006 and 28/03/2006

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