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MG TD TF 1500 - Crankcase Ventilation

There is link to a rather interesting articlein the MGA forum ( https://www.mgexp.com/forum/mga-forum.2/mga-crankcase-ventilation-test-results.4476585/ ) that gives me pause to wonder whether my rocker cover vent system is working. How have others who at using pancake style air filters accomplishing RC ventilation? Thanks. Jud




J K Chapin

There are a couple of threads on the US Forum on this very issue for the T series, involving consideration of the MBG PCV system. A more recent development is to use a system to create a venturi effect using exhaust pressure to vent the crank case. Early tests seem to show promise as this does not affect idle-related variables.

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

Because I have had good results from the Smiths PCV system on other BMC cars, I retrofitted one to my TD. This causes a slight vacuum on the crankcase and my car is amazingly oil leak free perhaps because of this.





John Quilter (TD8986)

No impact on your idle John?
M Hyde

Been a long time since I fitted this but I might have adjusted it slightly at the time.
John Quilter (TD8986)

Lonnie, you might find this thread interesting. In my humble, VERY non-expert opinion, you're OK for your planned trip.

Jud
J K Chapin

Looking at John Quilters excellent installation of PCV valve would this involve blocking off the rocker cover vent ?
Gss Smith

I have been running the Archie McAllister crankcase pressure reduction system described in the second post here - for 2 and half years now. I have had no leaks from front or rear seals since.

Merv
M Hyde

I think I have the most recent McAllister modification. See thread titled "Help with modified crankcase ventilation (PCV)".

I did quite a bit of work and research and I think this method is the simplest and best. It uses the exhaust flow velocity to create a negative pressure to suck out the crankcase gases into the exhaust. It has zero effect on carburetion. It is basically an improvement on the stock down tube arrangement.

I elected to insert the device (sort of a pitot tube) behind the muffler, others inserted it before. Both work, I can't say which is better.

Jim Barry
J Barry

Same set up I believe Barry, except my venturi take off is BEFORE the muffler. I changed the original one-way valve after 6 months to one that did not cause sooty build up. It works really well in the rev range of these motors.

Merv
M Hyde

Merv,

Yes, we discussed this before. I measured an inch of water vacuum at idle, which I think is pretty good. The problem I found with going past the muffler was a much longer hose run, and the need to keep the run straight to prevent water blockage. The one-way valve is meant to be a spark arrestor. I installed it, but I'm not sure it is necessary, especially behind the muffler.

The following link shows the vacuum kit being discussed. The blue hose is a safety by-pass, and the black device is the one-way valve/spark arrestor. I saw no need for the safety by-pass or an oil catchment. This device is being sold for airplanes that run at full revs all the time.

In short, the system is simply a hose from crankcase breather (remove the draft tube and install a short pipe) to the pitot tube hose-clamped to the exhaust pipe. A hole has to be drilled into the exhaust pipe to accept the pitot tube.

https://antisplataero.com/product/crankcase-vacuum-kit-complete/
J Barry

Yes Jim. That's the one i bought as well - locally - from an aircraft supplies company. I found that the one-way valve tended to get stuck with soot after a while. Easy to clean but I advised the company and they replaced it. The replacement has never had a problem and stays clean. I also find that the catch can (on the LHS on my RHD car) seems to collect very little oil (condensed vapour), when I check it every 3 months.

Merv
M Hyde

I’ve found these threads interesting in the subject but question the need. It is this a bandaid approach to a problem not being addressed.

I’ve been building stock and high performance Xpags for ten years now. My fast road engine in TD-4834 being my first. The engine was built originally intended to road race but life and plans changed. It was designed with parts for sustained high rpm usage. It is not sedate on the streets. Normal off idle use is 4000-6500 rpm 90% of the time. It now has over 4000 mi on it. The engine has run the SU branded open element air cleaners sold from Moss but now is running screened velocity stacks. I do not have any substantial blow by issues. I’m using a cast valve cover with no ventilation, a smooth cast side cover with twin breathers. No road draft tube. The front and rear seals crank seals are upgraded. Volvo seal up front and the Moss seal at the rear. Lastly I’m using Tom Lange’s “Roadster” gaskets fit the rocker and chest covers. I’m not experiencing any appreciable oil leak issues or blow by venting from chest cover breathers. Again this engine is operated at much higher rpms than most owners of XPAG/XPEGs care to run them. But these engine were intended to be run at 5000 rpm all day long when new. These are sports cars after all and meant to be driven in a sporting manner.

So I guess my thoughts on this subject would be .. is the crank case venting issue more about blow by from a tired engine that needs inspection or faulty prepwork during assembly and break in procedures The road draft tube on the stock engines is certainly large enough to vent a healthy engine. One could also extend the tube with a rubber hose to put its exit point lower and unobstructed to cleaner air flow when the car is in motion. The air flow rushing passed in effect providing the same negative pressure at the exit point just as routing it through the exhaust providing the same venturi extraction effect.

I dare say the only reason there is a vent in the stock valve cover is to extract any condensation that may be trapped from heat cycles, coolant leaks and/or humidity.

Just my thoughts on the subject.

Bill Chasser
TD-4834
TD/c-8151

W A Chasser

Hi Bill,

I'm not an expert by any means, but I did encounter quite a bit of information when I was doing my research. One of the main reasons for crankcase ventilation is to prevent oil contamination from the crankcase gases. The road draft tube can work quite well for this, but it does nothing when the car is not moving. The crankcase gases can also be quite noxious when sitting at a stop light, for example, as my wife can tell you.
J Barry

This thread was discussed between 11/08/2022 and 20/01/2026

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