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MG TD TF 1500 - Help with modified crankcase ventilation (PCV)

I've done as much research as I can, and I now figure that my oil leaks are due to inadequate crankcase ventilation. Our cars are equipped with a road draft tube that is suppose to suck vapors out when traveling at speed creates a lower pressure at the end of the tube. Of course, this does not work at idle (except if the tube is in the fan slipstream?).

Modern cars seem to use both a pcv valve to route vapors directly to the cylinder intake manifold, and draft tubes that dump into the air intake before the throttle body or carburetor. I am thinking of trying the latter route.

My plan is to contrive a path from the side cover draft tube outlet into the air intake just past the 90 degree turn from the air cleaner. I have a 3/8" fuel hose barb fitting with a 10mm threaded end that I plan to thread into the aluminum intake. I think the intake velocity should be high enough to create low pressure in sync with engine rpm's.

I haven't seen this done and would appreciate any input before I drill a 10mm hole into the carb intake.

Thanks,

Jim
J Barry

Its been done by many. I drilled the carb insulator blocks instead of the carbs or manifold, then used a Y junction and an MGB type PCV valve.
Dave H
Dave Hill

Thanks Dave. Apparently there is a difference as to which side of the butterfly valve is used. Then engine side uses the vacuum created by the piston downstroke. A pcv valve is necessary to regulate the vacuum. I'm proposing to use the air filter side where the flow is steady and in sync with engine rpm. I think the flow velocity should be enough to create an adequate pressure drop similar to what happens in the carburetors as air flows over the jets. If I'm wrong about this, I surely want to know.

Jim
J Barry

Well, I've answered my own question. I made a simple manometer and tried to measure the pressure drop before the carbs. There is basically none at idle. Goosing the throttle (probably to around 3K rpm) gives about 1 inch of initial water column displacement, but it quickly settles back down to about 3/8" max. So no, this method is not going to work.

Jim
J Barry

I fitted one of the Aircraft Spruce venturi systems that Archie McAllister developed for the T cars. Creates a solid vacuum for crankcase ventilation. Any remaining leaks are due to poor gaskets.
M Hyde

I looked up the venturi systems at aircraft spruce, but did not see the MG application. Still, they look really interesting. Can you provide more information - maybe photos of your installation?

Thanks,

Jim
J Barry

Jim this thread shows Archie's original approach https://www.mgexp.com/forum/t-series-and-prewar-forum.46/td-pcv-instalation.4295691/

There is another thread including my RHD application and various images. It is very effective.

https://www.mgexp.com/forum/t-series-and-prewar-forum.46/pcv-valve-use.4528602/page-2
M Hyde

Merv,

Thank you for this, it is intriguing and may well be the solution I'm looking for.

Jim
J Barry

Jim, there is more feedback on this system today from Archie McA, after 11,000 miles of use. https://www.mgexp.com/forum/t-series-and-prewar-forum.46/supercharger-and-pcv-plumbing.4662750/
M Hyde

Thanks Merv. I went ahead and ordered. I like the cheap Chinese catch can too.

Jim
J Barry

Years ago I rigged up a Smith PCV system borrowed off a later MG like an MG B or MG midget. It uses the factory Smiths valve but the plumbing was custom. Seems to work fine and minimizes oil leakage from the rear main as it creates a small vacuum on the crankcase. Would not be acceptable to those who insist on totally stock for concours.







John Quilter (TD8986)

John, how did you plumb into the manifold?

Jim
J Barry

SEE http://www.ttalk.info/TinkerServo.htm for a tap for a power brake system. Mine is a bit different. Bud
Bud Krueger

Based on reports over time the adapted MGB PVC system isn't as effective at reducing crank case pressure and can reportedly play-up with idle parameters. The system that Archie developed doesn't.
M Hyde

This is the easiest system to install and it works! Aircraft Spruce crankcase vac system. PJ

Archie M. picture of exhaust connection.



PJ Jennings

Exhaust connection. PJ



PJ Jennings

@ J Barry Hawaii. Drilled and tapped a hole in the manifold for a pipe nipple. Did add a small tube to spread the vacuum to closer to the center of the manifold where the PVC valve should be but doesn't fit due to the aluminum intake plenum.
John Quilter (TD8986)

Mine leaks only from the real seal. Sometimes it's a little, other times more. Hard to say exactly how much and to what extent it's caused by built up crankcase pressure. That said, the Aircraft Spruce approach seems to be pretty good to assure such pressure is kept to a minimum. My question is regarding additional plumbing and use of a catch can. I would not think the installation of the Aircraft Spruce vacuum attachment would result in anything more than fumes being drawn out, and those would burn off in the exhaust. Am I missing something that warrants a interim catch can? Jim

Jim Rice

Jim there is a solid venturi effect created in the exhaust mounting with the angled edge of the Spruce attachment. That said, I have found very little oil (maybe 1mm) occurs in my catch can over the last 6 months. I did have a small stainless steel gauze in the line to the catch can.
M Hyde

I am in process of installing the system aft of the muffler. Some of the research I did indicates that these systems are not meant for exhausts with mufflers. I phoned Allan Nimmo at AntiSplatAero, who builds the systems and he stressed that these are built for airplanes and the engines go full throttle all the time. He said that people put them both before and after mufflers on airplanes, but that he would be inclined to put it behind the muffler on a car. My thinking is that a muffler is an area of high pressure (lower velocity). The entire exhaust run has to be above atmospheric pressure, with the lowest pressure near the end of the pipe. The exhaust velocity has to be the same on both sides of the muffler, so it makes sense that the lowest induced pressure would be after the muffler. I did a crude manometer measurement after installing the gizmo and found it pulled about an inch of water at idle, which I think is pretty good for this purpose. It's a long run to the back of the car, and I realize that the run should be fairly straight so as to not create a water block.

I'm going to leave out the catch can for now. It probably is not necessary, and installation options are limited.

John Quilter, thanks for the installation info.

Jim
J Barry

We have all successfully used a position before the muffler Jim. Will be interested to see how your position goes, however.

Merv
M Hyde

Merv:

When you installed the attachment, was there any thought or consideration in enlarging or adding additional holes in the side cover gasket to improve ventilation/scavenging? Don't know if that would make any difference or not.

Jim
Jim Rice

Jim, I did think about that aspect but I was more persuaded by the notion of using the Venturi effect offered by this approach to create greater -ve pressure on crankcase gases, while driving. Archie and some others have measured the pressure with useful results.
M Hyde

So the installation is done, and I am astounded at the result. When I put my hand over the open oil filler at idle, the suction is quite strong. I think it is way more than enough for the job. I'm not sure if my front seal leaks are gone, but limited data indicate the situation has at least improved.

We ginned up a new down pipe using 3/4" and 1/2" copper pipe fittings going to 6 1/2 ft of 3/4" hose. A 45 deg pipe fitting (1/2") on the vacuum gizmo helped keep a flat run of the hose. According to the fabricator, the valve in the system is a flame arrester, and not needed for most cars. I kept it on anyway.

Thank you Merv for alerting me to product. I think it is a great solution for crankcase over pressure on our cars. As to the before muffler or after muffler question, I can only say that after muffler works well. My next go-round I may try to make some solid measurements.

Jim



J Barry

Great Jim. I can't take any credit at all as Archie McAllister was the originator of this process, that I also followed. My rear sealant side cover leak disappeared and the front seal one reduced (I do need to fit the new speedi sleeve, front timing cover seal and pan gasket that I have ready to go, if ever I stop driving ...
M Hyde

This thread was discussed between 12/06/2023 and 19/06/2023

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