Valve cover breather??

Hi, I'm replacing my valve cover that does not have a rear breather tube. Do I need to vent someplace else? of just not worry about it? 18v engine
thanks
paul

I drilled the rear of the cover and put in a brass elbow to vent the cover to the charcoal canister. I had to seal the vented cap with a small metal MG logo held on with JB Weld.

That elbow on the valve cover is actually pulling a small amount of air in, so I guess you could attach a tube with a small hole at the end and maybe also install a filter like the ones sometimes used on the tappet cover breather tube.

It needs only a very small breather hole, so on a 1/2" line you will need a copper freeze cap with a small hole drilled in the cap. I believe its 3/32, but I'm at work and can't check just now.

The hole is 5/64"

http://www.mgexperience.net/article/mgb-pcv-system.html

I replaced my stock cover with a aluminum and drilled and added the pipe to go to the canister per spec, but if I read the above attached article correct then I need to be sure that the cap is a sealed cap.....correct? I did not even check the cap

Yes, you should use a sealed cap otherwise you'll end up with about a 1/4" hole (total of the two holes together is 13/64") which can be a fairly substantial vacuum leak if you have everything else connected properly.

So, let see if I have this. If it is a stock engine I need to have a small hole with a fitting for a hose that comes from the canister.and a sealed cap. If I have a desmoged engine
I can use a vented cap and not have to install the rear hose fitting.
thanks
psul

Paul, that sounds like a workable solution. The whole idea here is to allow a small draw through the engine without creating too much of a vacuum leak at the carburetor(s).

If you want to continure sucking the gas vapors from the canister you must install a fitting in your new valve cover that has a 5/64" restricted opening, and the valve cover cap must be sealed. Otherwisw; you can disconect the canister, and just use a vented cap with the new valve cover.

Just throwing on a vented cap may not work, you'll have to look at the rest of your plumbing, if you leave the line to the canisters open I think you will be introducing a vacuum leak as the canisters are connected to the carburettors. Also, if your block is vented through the front tappet cover to the backs of the carburettors adding a vented cap will also introduce a huge vacuum leak. Your set-up will depend on the year of the car and any DPO modifications.

Not to harsh on you Mike, but the carbs are connected to the cannisters at the float bowls. This will not create a vacuum leak but rather cause the anti-runon system to malfunction.

I agree that if you're going to run a vented cap and not plumb the line to the cannisters then you should cap the cannister so that the anti-runon will function properly.

1/8" "leak" with a vented cap vs 5/64" "leak" with non-vented cap and properly vented valve cover is a .05" difference. This really boils down to richening the carbs a little.

There's a reason I threw away all my plumbing and went Euro-spec Eric - it's a whole lot simpler to understand! :)