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MG TD TF 1500 - TF Rocker Cover Blow By?

I noticed a steady blow of air coming from the rocker cover breather on my wife's TF681 (1250) while tuning it yesterday. I don't see water vapor, smoke, or oil droplets from it. I can barely feel air from the engine breather tube. Do I have a problem?

Compression is uniform at 140-145. Freshly set valve lash at 0.013" cold. I looked into the cylinders with a bore scope -- to my untrained eye, they look clean, no coking on piston tops. Valve train and top of head are clean. She bought the car in March. I don't know much about the history of the car. Based on compression and visible condition of head and cylinders, it may have had some engine work recently.

Oil level slightly below FULL. Oil pressure is slow to build on startup; maybe five+ seconds. 40-45 PSI at cold idle. 20+ at hot idle. 40-45 PSI at speed. Early oil pickup to the gauge at crankcase instead of at head. Valvoline VR-1 oil.

Water is clean. The level doesn't drop. Water temp 90-deg C.

Starts on first pull, with choke. Black soot/oily droplets from exhaust on cold startup. Clean after engine is warm. Smooth sound from tail pipe. Tissue does not suck into it at idle.

YouTube video:
https://www.youtube.com/watch?v=yNhJOnnh2hI

Thanks for your help,

Lonnie
TF681
TF7211


LM Cook

Lonnie,
Could it be a little blowby getting past your exhaust valve guides? If bronze, they must be a little loose to prevent ceasing when hot. From what you said re compression and viewing the boars it all sounds good there.
Rod Jones

Thanks Rod,

Interesting. The air coming from the rocker cover breather seems to be pulsing, which could be from a valve guide.

There is a lot of air coming from the breather.

How bad is it if the air (exhaust gas) is coming from a valve guide? What damage will be done?

Lonnie
TF681
TF7211
LM Cook

The pulsing is simply the pistons going up and down in the engine blowing air back and forth in the crankcase.
The valve cover breather is directly connected to the sideplate breather via the pushrod holes etc.
For a try, If you block that top tube off then the wind will/should go out the bottom tube
If it doesn't then there is a blockage in the bottom breather somewhere.
There will always be some pulsing in the breather
William Revit

>> A small amount of pulsing air is coming out of the crankcase breather when the engine is running.

>> Jo Ann covered the oil filler opening and the breather opening on the rocker cover while the engine was running at about 1200 RPM. The amount of air coming from the crankcase breather DECREASED to almost nothing.

>> Is this a major problem? Minor problem? No problem?

We are driving the car about 275 miles round-trip to the All-British Field Meet in Safety Harbor, Florida, next weekend. MG is the featured marque. Is it going to self-destruct?

The video doesn't adequately show the amount of air coming from the rocker cover. I made a paper towel flag attached to a screwdriver shaft and placed it by the rocker cover breather - looks like Old Glory blowing in a storm. I can make another video if needed.

As noted earlier, no steam, oil, or vapors come from the rocker cover breather or oil filler opening.

Thanks for your help.

Lonnie
TF681
TF7211
LM Cook

I removed the crankcase breather tube. Dirty, but not blocked.

Lonnie
TF681
TF7211
LM Cook

Lonnie, you might find the thread below that I just reactivated of interest. I suspect the bottom of the pistons going up and down in the crankcase are pumping air up through the pushrod holes, into the valve cover and out the little pipe. I haven't checked mine but I bet that's normal.

Jud
J K Chapin

Thanks Rob, William, and Jud.

No one predicted that we will be blown into the next dimension, so I'm gonna bolt on the Vokes air cleaners and enjoy the drive.

(The wind from the rocker cover may be common. I probably never got close to the breather on TF7211 while the engine was running.)

Lonnie
TF681
TF7211
LM Cook

Just for grins, here's my valve cover "breather."

Jud

ps: This pic ws taken circa 2012. The engine bay has been cleaned up a bit since then.

J K Chapin

A follow-up for future readers of this thread in the Archives ...

I have attached the article that is in the "Crankcase Ventilation" thread that Jud mentioned.

MGA_CrankcaseVentilationTest.pdf
See the last diagram in the article. It pretty much answers my question. (Eleven pages. Don't know if all are visible on a smart phone.)

Thanks again, Jud, for your help,

Lonnie
TF681
TF7211
LM Cook

This thread was discussed between 12/10/2022 and 17/10/2022

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