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MG TD TF 1500 - Vacuum prevent oil leak

Intend to try a PCT valve from a MGA for evacuating gases from the crank case, in combination with a none return valve on the breather pipe, (see image)in order to reduce oil leak. In the adapter between the rocker cover and the valve is screw for adjusting the flow. Read somewhere that the equivalent of a 3 mm. hole could be reasonable, not to affect the fuel mix too much. I think it should be a bit smaller thou.

With closed throttle I guess the pressure in the inlet manifold might be around 0.3 bar, depending on rev. The pressure in the crank house will of course be much higher, but hopefully below 1 bar for periods long enough to prevent oil leak - mainly from crank ends.

It got to be an engine in fairly good condition. Otherwise the none return valve will never close.

Anyone who has experience of a similar set up?

Image of set up in comment below.


YS Strom

PCT valve set up

YS Strom

Its been discussed several times before - look in the archives for PCV.
Dave H
Dave Hill

YS,
You need the right PCV valve. The part no is shown on the drawing. It is not just a non return valve.
http://mgaguru.com/mgtech/engine/cv103.htm
I use a 2.1mm restrictor to each side of the inlet manifold. If you use a Wolseley 4/44 side cover it has an integrated flame trap.
When you close the throttle the pressure at the inlet manifold will be more than the the 0.3bar you have stated. I measured 0.7bar on my car.

Regards
Declan

Declan Burns

Here's a photo of the installation with the Wolseley 4/44 side cover. I will change this to copper pipe instead of vacuum hose to the inlet manifold over the winter. It is amazing how little oil ends up in the drip tray.

Regards
Declan

Declan Burns

As you mentioned Dave, there were a lot of interesting comments on this in the archive. Have not read them all yet, but so far I have not found any with a none return valve fitted to the vent pipe. If plugged I guess pressure might easily build up under certain circumstances and be counterproductive, even with a fairly good engine and a hole 1.5 mm. as recommended in an interesting comment in the archive. With a none return valve vacuum is likely to be extracted for periods long enough to reduce oil leak with a smaller restrictor, thereby interfering less with adjustment of fuel mixture and idling.

Realized also that I have to make sure the cap on top of the rocker cover is tight, which I thought they all were.
YS Strom

I've been running a Smiths PCV on my TD for a number of years. Here is the plumbing from the accessory aluminum tappet cover. The valve can be seen just under the air filter assembly above the intake manifold.



John Quilter (TD8986)

Thanks for your interesting comments.
But have you installed a PCV for environmental reasons or for reducing oil leak? If the vent pipe is not blocked or a none return valve is installed, I can´t see how it could reduce oil leak. So far I haven´t seen any information on this.
YS Strom

You get both for the same price. A properly designed system routes engine fumes to the inlet manifold using manifold depression. The same manifold depression helps to reduce oil leaks.
Dave H
Dave Hill

Surely most of the potential areas for oil leaks are under 45 psi pressure. Two that aren't are the tappet and rocker covers but both these have vents.

Jan T
J Targosz

Not so Jan. The oilways and bearings may be under that pressure but the rest of the crankcase, and sump are not.
Dave H
Dave Hill

Hi Dave,

I agree but where would oil leak from the sump or crankcase? The three main areas are the front of the crank, the rear of the crank and the join between the sump and the block. For negative pressure to have any effect on the first two it would have to pull through the crank journals and bearings - an impossibility. It may work with the sump flange but a high vacuum would be needed and I don't think this is a problem area.

Cheers

Jan
J Targosz

Jan,
That is exactly how it works. You get infiltration air coming in through the rear scroll due to the regulated vacuum pressure. Where air is drawn in, oil cannot flow out. It works and a lot better with the original Smiths valve than with the first valve I tried which was in effect a non return valve from a Ford Pinto. There has been hardly any oil in my drip tray this year.

Regards
Declan
Declan Burns

Hi Declan,

Yep I have just been looking at a cross sectional drawing of the engine. Oil under pressure enters the rear bearing from the gallery and exits from each side. For the inner it simply runs down into the sump. At the outer side it collects and runs down the drain tube, again into the sump. The scroll should prevent any of this leaking to the rear of the flywheel. I now concur with you that a partial vacuum in the sump will evacuate the area to the back of the scroll via the drain tube and discourage oil from leaking past the scroll. Having said that I have a lip seal fitted to the front of the engine (now the correct size and not one of those from the regular suppliers) and a catch tank at the rear and there are absolutely no leaks.

Have a good weekend

Jan
J Targosz

I’m totally inexperienced in these matters but keen to learn as my naked block is on a stand at the moment with many decisions waiting to be made. I have seen mention of the fact that the original breather tube from the tappet cover extends down into a low pressure area below the engine. To counteract oil leaking via the scroll, a depression in the sump would have to exceed the depression outside which only exists when the car is in motion. Is there any data on these pressures?
I recently showed pics of the various oil leak mitigation solutions to the machinist I use and his comment was that the original system sort of works “for these old bangers” as long as you don’t park on a steep slope. Is the oil level in the sump that close to the seals?
Chris
C I Twidle

Hi Chris

I am also new in the MG field, but I have tried for a while to eliminate oil leak.
As the shaft and bearing have worn, the shaft eats down and widen the clearance in the Archimedes screw. Therefore I think it is unlikely you get it tight just by the Archimedes screw.

Using the Moss seal can do the job, but there are many who have failed. So did I once. Note that Moss gives no guaranty. One of many reasons for leak is that the drainage from the seal housing is too high. Therefore the flange will rotate in a pool of oil and act as a centrifugal pump and build up an oil ring in the periphery of the seal housing. Therefore I have modified it with an extra drainage at the bottom of this pool. You can find more about that in the archive.

When using their sleeve there is a high risk the seal will be damaged when installing it. They recommend using masking tape when installing the seal, but I have found it be better using the brown thin tape used for packing. It is thinner an glossy.

As mentioned above, I am in the process of trying a PCV for creating vacuum in the crank house, to see if it will solve the problem. However, at high load there is low vacuum in the manifold and the blow by over the pistons are likely to be high. To let all that into the manifold might give problem adjusting the carbs - specially idling - also depending on the condition o the engine. Therefore I intend to use a none return valve in combination with a PCV. It might be enough thou to lift the foot a few seconds every now and then, to extract the oil from the Archimedes screw.
YS Strom

This thread was discussed between 20/11/2017 and 26/11/2017

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