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MG TD TF 1500 - PCT valve

Have now completely overhauled my XPAG and tested it in the workshop. I also tested it with a PCT valve on the valve cover and connected to the inlet manifold, to see if it could be used to create a vacuum in the crank house, in order to reduce oil leak. A none return valve was fitted to the vent pipe, as described in an earlier thread. But even with an orifice of 2 mm. dia. the none return valve closed only for very short periods. It actually vibrated. So I think PCT valves can only be used for evacuating harmful gases, but not for reducing oil leakage. With a bigger orifice it might work, but will most likely affect the fuel mix too much.

Well, it was a good try.
YS Strom

For any kind of PCV valve to work the crankcase must be a clis d system for that to happen the road draft tube must be plugged.

Bill Chasser
TD-4834
W A Chasser

YS,
I think you have got it wrong.
The best results are obtained using a crankcase breather valve 13H5191 from an MGB, Sprite/midget, Mini Cooper S, TR4A. This is not a non return valve-it is a vacuum modulated flow control valve.
See
http://mgaguru.com/mgtech/engine/cv103.htm
The breathing system must be a closed circuit and the road draft tube is not plugged-it is connected to the inlet manifold via a restrictor.The side cover can be replaced by a Wolseley 4/44 side cover which has an intergrated flame trap. I have a spare one which I might sell if you need it.
The vent on the rocker cover is plugged and the oil filler cap must be sealed as well as all other sources of infiltration air!


Once again the principle drawing

Regards
Declan



Declan Burns

YS,
I have a detailed installation workshop drawing for this system but cannot upload it here in jpg format due to file size restrictions and this website will not accept pdf's. If you need it send me your email address.

Regards
Declan
Declan Burns

If you send me the file I can convert to JPG and reduce size so it can be posted.

mgtd52-at-btdtrf-dot-com

Jim B.
JA Benjamin

A none return valve was fitted to the vent pipe from the tappet cover and the PCV valve, I have been told, comes from an MGA as shown in Declans link and image. I.e. the none return valve opens when the pressure in the crank case exceed atmospheric pressure and closes if the evacuation via the PCV is greater than the blow thru between pistons and cylinder walls, which never happened in my case.

Maybe after the engine has been broken in, the leak between walls and pistons will be reduced.

It is worth noting that there is a pulsation taking place as the pistons on the way down will press down the total swept volume, but the pistons on the way up will due to the inertia of the air evacuate less from the crank case before they turn and go down again. With equal pressure on both sides of the none return valve it was closed. That made the none return valve vibrate.

If anyone has tried to block the vent pipe and installed a PCV it would be interesting to know how much the pressure in the crank case has been reduced. It would also be interesting to know how much vacuum they are set to give, as if too high they are meant to close.





YS Strom

Jim,
I sent the pdf through to you.

YS,
When I first installed the system using a Ford Pinto non-return valve and without the restrictor, I measured -120mm water gauge = -12mbar on the u-tube at idle and connected as shown above.
I also temporarily installed a vacuum gauge at the inlet manifold which read -0.7bar! The vacuum gauge on the manifold required a cigarette butt filter in the piping to prevent the gauge needle going into orbit.
At this setting the engine idle was very erratic.
I started introducing restrictors to each inlet manifold. Starting at 3mm and going down in size the idle started to improve.
I stopped at 1.7mm in each manifold which would equate to 2.1 .. 2.2mm if using a single tapping point.
I never actually measured the pressure with the 1.7mm restrictors as the system is now, but an intelligent guess would suggest approx. -0.3 ... -0.5mbar. The engine idle was constant.
The oil leak reduction was significant and easy to see through the level indicator on my drip tray.
The major breakthrough came when I swapped over the non return valve for the MGB modulating valve. I could see hardly any oil leak and in fact I only had to drain (very very little oil) from the tray over the WHOLE driving season last year.
That was what I call an improvement!

Regards
Declan




Declan Burns

Many thanks Jim!
Here's the drawing.
Detail X,-the restrictor is still missing at this stage.
Regards
Declan


Declan Burns

Jim has improved the resolution.
Regards
Declan


Declan Burns

Very interesting!!

The engine I have used is a totally renovated XPAG. I guess the blow thru will be reduced after a few thousand km. In my TD I have an also overhauled XPAW that leaked only 0.7 gr. of oil in 40 km. including two 30 min. stops and no drops in 15 min. after stop. This is ok. but I try the vacuum method because of my interest in experiments and innovations. I am not a purist, rather a developer and user.

The extra draining duct I made in the Moss kit made a great difference. The crank flange is otherwise rotating in a pool of oil and act as a centrifugal pump, building up pressure on the seal. The vacuum at idling is - 0.3 bar.

In Feb. I will try again with blocked vent and a bigger hose pipe between PCV and manifold and come back on that. Might also try with only a hose pipe, and a 2.2 mm. restrictor as per Jimīs advice.

Am I wrong if I say 120 mm water = 120 mbar? Anyhow, 120 mm. water will certainly make a big difference to the oil leakage.
YS Strom

120 mmH2O = 11.8 mBar.
A bar is almost Atmospheric pressure, 14.5 psi

Jim B.
JA Benjamin

Yes, of course, you are right about the pressure.
YS Strom

This thread was discussed between 17/01/2018 and 20/01/2018

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.