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MG TD TF 1500 - Crankcase Pressure

Hi All.

Thanks to all of you who have given advise in the past I am really enjoying my TD. I have already put over 700 miles on the car and it is running better all the time. The question I have now involves the aluminum rocker and tappet covers and their effect on crankcase pressure.

I still have oil leaks although they are not excessive but a member of our local car club (and a British Car mechanic) seems to think that I have too much crankcase pressure building up. I stress that the engine runs fine and it is not smoking anymore and I am aware that some leakage from these engines is normal. He did get me thinking about the engine venting though and the following appear on my engine, the valve cover has the cap near the firewall and is vented so this should be fine for the fumes in the top of the engine. The tappet cover has a removable cover on the side that should vent the fumes from the bottom end of the engine but when I removed this cover it has a cork "seal" that effectively blocks this off.

Does anyone know what was intended to be inside this vent, if anything?

I have considered going back to the stock setup but am missing the downpipe from the original tappet cover and I really like the look of the aluminum at this time.

Brian SMith
Brian Smith

When i took off my side tappet cover (finned aluminum add on), the gasket had a cutout for that vent area (mine has a weird pipe going up to a homemade breather that collects the "oil" and lets it drip back down into the engine).
gordon lawson - TD 27667

Actually... could there be a build up of crankcase pressure... with all the vents, even with the tappet cover's not open, there is a direct line up to the valve cover and a rather large vent in it.... I would tend to think that there is anything but pressure? Correct me if i'm wrong!
gordon lawson - TD 27667

Gordon

Thanks for the input. I haven't felt there was a problem but this fellow was sure that it had way to much crankcase pressure. The valve cover is vented quite well and the engine runs well now so I don't really see a problem but when I took the tappet cover off I noticed that, like yours, it has the cork gasket between the tappet cover and the engine with an opening cut where the breather is located but the removable breather has had a piece of cork inserted in it that would effectively block any air from moving in or out of the engine. I was wondering if this breather should be open without anything in it or if there was something else originally in there. Taking the cork out would open it up but would it lead to more leakage of oil?

Brian
Brian Smith

Gordon:

Interesting observation. I happened to have a couple old gaskets for the tappet cover and noted that the older ones do have a hole for the breather, but the new one's do not.

The holed for the tappet bolts appear to be exactly the size of the bolt. May get a litte pressure relief from this area, but it may be good to add in the hole for the breather.

Bruce Cunha

Hi Brian, the side plate should vent through the pipe provided. I would punch a couple of holes in the gasket, but they absolutely have to be close to the bottom of the gasket. If they are higher or level with the breather pipe the oil builds up between the gasket and the side plate and runs out the breather pipe.

Believe me mate, been there done that.

Good luck,

Paul.
Paul van Gool

The chap who rebuilt the car in '67 was a racer on the Canadian circuits...He added a strange little breather thingie to the tappet cover vent... copper 1" pipe going up to a little breather... the one time i had the top off, i found oil residue in the breather, however, it just drains back down into the engine?

http://www3.sympatico.ca/gordonblawson/td/td106.jpg

Seems to work as i lose no oil on that side.....?
gordon lawson - TD 27667

Gordon;
That breather looks like a good idea. I am certain because of the solid screw-on valve cover cap that it is needed.Is that breather the only way for the crankcase to vent?
Sandy Sanders
Hudson Florida
conrad sanders

Whenever I instal a new tappet cover gasket on my TF motor, I punch a row of holes (about 1/2" dia) along the bottom of the gasket just above where the bottom line of the gasketis to seal against the block. I was advised to do this many years ago by a friend who was experienced in XPAG/XPEG motors. It helps considerably in helping to avoid a build up of crankcase pressure.
Peter Daley

There is no vent on the valve cover... the vent tube on the breather filter is just sitting there with no tube connected. Assume it has been that way since '67
gordon lawson - TD 27667

Wonder if I should tap the cover and add the tube up to the air filter?
gordon lawson

Could you put on a vented Oil fill cap?

dave
D. A. Braun

I would hate to change the cap as it is a replica of the rad cap...really solid casting.
Haven't had a problem with how it is set up now, just wondering if it might be better vented into the breather.
gordon lawson

Go to http://mgaguru.com and the tech section. Read what Barney says about the vent system of the MGA. It should also apply to the TD. That is, fresh air is supposed to come from the air cleaner into the rocker arm cover, mixed with the fumes in the crankcase, and everything goes out the draft tube which is in the air stream under the car. Air moving across the open end of the tube "siphons" the fumes out.

Regards,
Blake
Bullwinkle

Hmmm... with the rubber hose going from the valve cover to the air cleaner (unless there is some special thing in the air cleaner i've never seen), i can't see how, with the amount of suction at the carb intake, that fresh air would go down the tube and into the vc. The system to me would have to suck from the valve cover into the carb....
gordon lawson - TD 27667

Just about all the relevant text books I've read state that the rocker cover fumes are sucked via the hose through (normally) one carburettor into the engine to be burnt. This also helps to reduce crankcase pressure, which in our engines should be minimal, owing to the existance of the vent pipe on the tappet cover panel (provided the cork gasket has the normal holes in it).
Roger Wilson

In my case the valve cover is vented through the cap on the valve cover but the tappet cover has a small aluminum cap with MG cast into it and this particular cover was blocked totally by a previous owner with a piece of cork similar to the gasket material. It would not appear to be functional for venting. Because it was an aftermarket cover I didn't know if it was meant to have the gasket or not but from the comments above I can only surmise that the vent should be open with no gasket. I am guessing that a previous owner left the cork tappet cover gasket as it came out of the package and oil built up until it came out this breather so to keep oil at a minumum the breather was blocked. The vented valve cover cap would take care of most of the pressure so the engine would not be adversely affected.

I have removed this tappet cover breather gasket and will try running it like this. My tappet cover is the same one used by Gordon with the exception that I don't have the fancy breather setup, this was the one that was blocked by the previous owner.

Brian
Brian Smith

I had what looked like a stock gasket with the hole under the vent opened up by someone over the years (looked like they used a rock....).
I cut a new one from cork and made an opening (with nice square corners...)
gordon lawson - TD 27667

Hi All

To update you on the crankcase pressure issue, I pulled the cork gasket material out of the breather on the tappet cover and took it for a blast, this created a real mess, oil blew everywhere but then the large cork gasket behind the tappet cover had an additional hole cut in it right behind the breather.

Took off the tappet cover, cleaned everything up, used gasket sealer between the block face and the cork gasket, once I had turned it upside down, and between the tappet cover and gasket and after taking it out for a couple of spins today there is no more oil in this area and the engine runs beautifully.

So....even though the breather on the rocker cover is open and works well, the breather on the tappet cover also needs to be open.

Brian
Brian Smith

This thread was discussed between 27/06/2005 and 03/07/2005

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