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MG TD TF 1500 - Positive Crankcase Ventilation

As I have the tappet cover plate off to fix a leak I had the bright idea of fitting a PCV valve to see if I could stop my rear oil seal from poluting the planet. Yes I've tried all the recommended ways of fixing it, line boring,fitting the seal kit etc.but after about 1000 miles they all seem to leak again and I'm fed up of taking the engine out. My engine fitter says that someone modified the bearing cap and unfortunately you can't get new ones.
Unfortunately I can't seem to find a supplier that sells the MGB PCV valve part No 13H5191 any more. You seem to be able to get most of the bits but not the main body. Does any one know of an alternative valve that does the job?
Also I understand it's wise to fit a flame trap/oil separator in the line. Any idea where I can get one of these?

Thanks

A
A R Jones

The standard engine is well vented to the atmosphere. Why do you think you have a pressure build up in the crankcase? Regards, Tom
tm peterson

A R,
I have a simple cheap Ford Pinto PCV valve with dual inlets (the blue spot) on my TD and connected this to a flame trap from a Land Rover. It makes a hell of a difference. I tapped both sides of the inlet manifold and I conducted extensive experiments last year on this issue. With the PCV valve installed I measured -12mbar crankcase pressure at idle with a U-tube manometer. It's a trade off between oil leak and idle. I now have 1.7mm restrictors between the inlet manifold and the PCV valve which in my case seems to be the optimum. Everything else is plugged off so the negative crankcase pressure draws in infiltration air through the rear scroll. Where air comes in -oil can't go out. It reduced a torrent to a trickle.

Regards
Declan


D Burns

I don't want to build the pressue up I want to reduce it. The idea is that the lower pressure helps stop oil leaks from the rear seal.
See the following for more details.
http://mgaguru.com/mgtech/engine/cv102.htm
I have now found a source for the MGB PCV but it's a bit expensive for something that might not work! I still have to find a suitable flame trap.

A
A R Jones

Thanks Declan.
I already have a hole tapped in the middle of my manifold, it's plugged with a bolt at the moment. I don't really want to drill another hole. I've now found a Smiths PCV valve, on the intenet. It was fitted to all manner of cars but costs about £55. Expensive for a bit of an experiment! Especially if it doesn't work.
I saw on the internet that you can get a Land Rover Discovery 1 3.5l Petrol V8 Flame Trap for about £5 but wandered whther it would be too big. Have you a reference for the one you used and does it fit in the line from the PCV to the Tappet Cover or the Rockker box cover to the air filter.

Thanks again

A .
A R Jones

Thinking about this I'm wondering whether fitting a simple modern pcv valve between the rocker box vent and the inlet filter and connecting the tappet cover vent straight to the inlet manifold would be a cheaper option. Anyone figure out why this won't work. It's effectively moving the pcv valve from the crankcase side to the inlet side.

A
A R Jones

A,
Land Rover Discovery-that's exactly what I used.
Here's a cheap PCV valve:
http://www.ebay.co.uk/itm/FORD-GENUINE-PCV-VALVE-/171871076125?hash=item2804507f1d

Here's the principle drawing.
Regards
Declan


D Burns

A,
Before you mess with the bolt in the manifold,check that it is not the one holding in the restrictor in the balance tube.If it shifts it can rattle about and mess up your mixture.
Ray TF 2884
Ray Lee

I knocked out the two core plugs and replace them with brass plugs tapped BSPT for standard barbed fittings and plugs.
Regards
Declan


D Burns

Looking at all the other old cars I've worked on, why not just put the PVC on the valve cover and route the hose to the air filter inlet, just like it is now on a TD. Just putting a PCV in the middle. No restrictors no anything else?

I'm not quite getting why all the extra plumbing and restrictors would be needed. Just put it in that little black hose, granted it would be atight fit and finding a right angle PCV would be ideal.

I don't have a problem with my car but it does sound like a good idea. and with an oil bath air cleaner, so what if a little oil gets in there.


L Rutt

I have my doubts that routing to the air filter inlet would be sufficient to put the crankcase under any significant vacuum pressure. I measured -700mbar vacuum on the inlet manifold at idle.

Regards
Declan


D Burns

Just how much vacuum do you think is needed on the crank case. All you are trying to do is keep a negative pressure, at any level, to prevent oil / air from being pushed out. That should only take a little bit.
L Rutt

I would think approx. -5mbar is sufficient. That is what we aim for in industry on large ducts to prevent dust emissions and I would think a similar value would apply in this case.-5 mbar is not very high. I measured -12mbar with the PCV valve on the inlet manifold before I installed restrictors to improve the idle.

Regards
Declan
D Burns

Once my TD is on the road, I do plan on putting in some sort of PCV system because I KNOW its going to leak. It did 47 years ago and in rebuilding the engine 25 years ago I did nothing to change that.

I do not remember the "Flame" trap in any of the cars I owned so I have been searching the internet for the reason these are used.

I did not find a good answer except that they collect excess unburned oil. They also clog up while doing that and should be changed frequently.

What I did fend is another approach.
One issue with how we are installing these devices is that by porting the valve into the intake manifold we scavenge the fumes and lower the crankcase pressure primarily at lower rpm.
As the carburetor valve opens and the engine speed increases the vacuum in the intake manifold drops. It is even possible for the manifold pressure to become positive. Its at these higher speeds we really want lower crankcase pressure.

I dont remember seeing a PCV valve go into the manifold. I remember them going into a spigot on the carburetor.

After reading some I believe this may be because the spigot was arranged to create a Bernoulli's Principle source of low pressure. This would actually increase with airflow as the carburetor valve is opened.

Now that was a long winded introduction to the reason fro this post.

There are Crankcase Evacuation kits on the market that add a (weld in)spigot to the exhaust pipe. This creates a source of low pressure that increases with engine speed and does not mess up the inlet side of the fuel system.

Here are several such kits.

http://www.summitracing.com/search/part-type/crankcase-evacuation-systems?sortby=Default&sortorder=Ascending&keyword=Crankcase%20Evacuation%20Systems&kr=Crankcase%20Evacuation%20Systems

Also here is a U-Tube video showing one working.

https://www.youtube.com/watch?v=wGrx2rvIxJ0

The more I look at this approach the more I like it.
I wish I had looked into this before I put the body on.

Just Search "Crankcase Evacuation System" for a lot more information.


Jim B.
Jim B in NJ

I have been running a Smiths PCV valve on my TD for a ew years. Seems to reduce oil leakage and fumes from the open vents on the aluminum aftermarket side cover.




John Quilter (TD8986)

And the side cover plumbing.




John Quilter (TD8986)

Very interesting.

Asked a mechanic if flame trap would be required if vent is connected to adapter between carb and supercharger (Eaton 42)? He said that it is often standard now with a hose direct from crank case to inlet manifold without any flame trap.

It may thou be advisable to make a long hole 1.7 mm. diameter,(as recommended by Declan) that might extinguish any flame.

Will very soon have this installed

Thanks for all information
Yngve
YS Strom

This thread was discussed between 03/08/2015 and 06/08/2015

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