Question re: Air Breather Valve on Tea 20's

Brad V · Apr 16, 2012

The air breather valve allows warm oil saturated air to be sucked from the valve cover and into the intake manifold for upper cylinder lubrication.
Since the oil saturated air mixes with the petrol/gas from the carburettor should this then result in the engine burning some oil and leaving an oil residue on the plugs?
My original air breather valve was missing and I drilled out a thick brass washer and inserted a stainless pin through it to keep it clean.
Perhaps my hole is a little too large and I end up having a greater flow of oil saturated air than is necessary.
My engine does not visibly burn oil but when I look at my spark plugs they do seem to have some oil residue on them and think that the way the valve system works that this would be normal.
Is it normal for this type of engine to use some oil during use as the clearances used during this era are much larger that the ones in use today?
I know my modern day car never needs an oil top up between oil changes.
Regards Brad

Charles in Aus. · Apr 16, 2012

Had to do the same to mine before I managed to
source a second hand part, they will not idle well
without this air restrictor. I used an Australian
copper one cent piece as the washer , a one eighth
of an inch hole is the appropriate size,idle speed
was good after this, after fitting the proper part
there was no change in idle , I took this to show
that the one cent piece was as good as the ten
dollar part! . If your engine did not use some oil
it would denote glazed cylinders,minor oil
consumption is far better than none in older
designs of engines.

John(UK) · Apr 17, 2012

When you say that the plugs appear to have oil residue on them, are you saying that the plugs are black and not a much lighter brown like you think that they should be. I have had this conversation before with "Bob in Oz" who tells me that the fuel in Oz when it burns leaves this black film and it is normal. It is due to a different composition of the fuel and he went into it at great lengths with some fuel suppliers. So maybe that is your problem. About the hole in the restrictor possibly being too big, it should only be about 1/8" dia. if if is too large, the Engine will run weak and you will noticeably have to open the Main Jet more to compensate for this, so if the setting on the Main jet is about right, then the hole is probably near enough correct. These Engines are not prone to using oil like you think although an old Engine like you have is bound to be using some unless you have just overhauled it and then you can expect that it wont use any at all. Does it throw out blue smoke when you open the throttle after idling for a short time, this would indicate oil down the Valve Guides, there are no seals used on these guides, this allows some oil to be sucked down on purpose for lubrication purposes.Having said that it should not throw out the blue smoke. Make sure that you have the main jet set correctly as obviously if it is set incorrectly it will use too much fuel and could color the plugs. There are more than one type of adjuster on these Carburettors and one of them has a snub nose needle, this type when adjusted should never be less than one turn open and it is no use opening it more than 2 turns as it will make no difference.The other types should be open about 2 turns for most work but again never less than 1 turn open. Having the main jet open more than necessary will cause excessive use of fuel and could cause the plug color you mention....John(UK)[email protected]

Jerry/MT · Apr 17, 2012

First let me say that I"m not nearly as familiar with the Standard engine as I am with the Z block Continentals.

The way the cankcase vent system works is that the crankcase fumes are vented into the valve cover and the orifice controls the flowrate of breather gases to the carb. Unless there is excessive blowby, there should not be a lot of oil going through the vent system to the carb. If there is, the there is a problem with worn rings or a cracked piston, that are causing the excessive blowby.

Excess oil on the plugs usually manifests itself as a wet oily deposit. A dry, fluffy deposit is caused by too rich fuel/air ratio and that should be able to be adjusted out.

An excessively large orifice would tend to lean out the mixture IF the crankcase fumes have a high air content(low ammount of blowby), or enrich the mixture IF the blowby (combustion byproducts)is excessive.
If you have a dry type coating on the plugs, I would suggest you try leaning the mixture a bit to see if that changes the situation. It might also be advisable to check the compression, both dry and wet, to see if the rings are worn.

The technology in these engines, while far lower than the modern automobile, is such that they are not prone to oil burning. They just plumb wear out.

Brad V · Apr 17, 2012

(quoted from post at 08:25:32 04/17/12) When you say that the plugs appear to have oil residue on them, are you saying that the plugs are black and not a much lighter brown like you think that they should be. I have had this conversation before with "Bob in Oz" who tells me that the fuel in Oz when it burns leaves this black film and it is normal. It is due to a different composition of the fuel and he went into it at great lengths with some fuel suppliers. So maybe that is your problem. About the hole in the restrictor possibly being too big, it should only be about 1/8" dia. if if is too large, the Engine will run weak and you will noticeably have to open the Main Jet more to compensate for this, so if the setting on the Main jet is about right, then the hole is probably near enough correct. These Engines are not prone to using oil like you think although an old Engine like you have is bound to be using some unless you have just overhauled it and then you can expect that it wont use any at all. Does it throw out blue smoke when you open the throttle after idling for a short time, this would indicate oil down the Valve Guides, there are no seals used on these guides, this allows some oil to be sucked down on purpose for lubrication purposes.Having said that it should not throw out the blue smoke. Make sure that you have the main jet set correctly as obviously if it is set incorrectly it will use too much fuel and could color the plugs. There are more than one type of adjuster on these Carburettors and one of them has a snub nose needle, this type when adjusted should never be less than one turn open and it is no use opening it more than 2 turns as it will make no difference.The other types should be open about 2 turns for most work but again never less than 1 turn open. Having the main jet open more than necessary will cause excessive use of fuel and could cause the plug color you mention....John(UK)[email protected]

Thanks John (UK) and others for your valuable input.
John I was not aware of the fuel issue you mention here in Australia that Bob in OZ discovered and suspect that all is fine as my tractor does not blow any blue smoke.
My Standard engine powered tractor does not have the original Zenith Carburettor and was replaced by a Schebler copy which runs very well.
The only issue I have with it is that since I use it to Slash/Brush hog the paddocks I have adjusted the main jet to 1 1/4 turns open as I don't wish to damage the valves by running it too lean.
My tractor runs the standard type of exhaust and it points in the direction of the safety chains and these are always coated with black soot (NOT OIL)from the exhaust which obviously means that I am running too rich.
I have noted your comments about never running less than 1 turn open on the main jet when working it hard and wonder if I should lean the mixture out to clear up the excess soot issue or should I leave it as it is as It does run great but it must be wasting a great deal of fuel. I would rather run it rich than risk damaging the motor.
Regards Brad

John(UK) · Apr 18, 2012

It is better to run rich than lean of course, but does the exhaust smell of unburnt fuel, if it does you could close the main jet slightly. Don't forget that the "Never less than 1 turn open" applies to the Engine the Carb was designed for and not necessarily the one you have. The jets in the Carb at this time maybe larger that those specified for the Engine in question. From what you say about the black soot on the check chains, it does appear to be too rich, I would try closing it a little and if it is too weak you should notice the Engine is not running correctly, it will be "splashy" in the exhaust rather than a firm power pulse as it fires. You can also get this if the Ignition is too far advanced. But to test if the Carb is set too weak or too lean, adjust the Carb to what you think it should be then run the engine at half throttle, then quickly open the throttle, the engine should speed up immediately without hesitating or throwing out black smoke. Black smoke is too rich and hesitation is too weak. Just keep trying this until you get it set correctly. Only alter the Main Jet setting 1/8 turn at a time.You should also make sure that the Air Cleaner is really clean, you may need to remove it and wash it out. Leave it soaking in some Petrol or kerosene overnight, the following morning allow to drain thoroughly before re-fitting to the tractor and filling with engine oil up to the mark. Make sure that you only adjust the carburettor when the Engine is at working temperature, any less and it will change its tune when the temperature rises. To set the Slow running/idle jet, make sure that the Engine is idling below 450rpm or it will not run on the Idle Jet, it will be still running on the main jet. If you have any other questions about any of this, just email me direct...John(UK)[email protected]

Brad V · Apr 18, 2012

(quoted from post at 08:34:25 04/18/12) It is better to run rich than lean of course, but does the exhaust smell of unburnt fuel, if it does you could close the main jet slightly. Don't forget that the "Never less than 1 turn open" applies to the Engine the Carb was designed for and not necessarily the one you have. The jets in the Carb at this time maybe larger that those specified for the Engine in question. From what you say about the black soot on the check chains, it does appear to be too rich, I would try closing it a little and if it is too weak you should notice the Engine is not running correctly, it will be "splashy" in the exhaust rather than a firm power pulse as it fires. You can also get this if the Ignition is too far advanced. But to test if the Carb is set too weak or too lean, adjust the Carb to what you think it should be then run the engine at half throttle, then quickly open the throttle, the engine should speed up immediately without hesitating or throwing out black smoke. Black smoke is too rich and hesitation is too weak. Just keep trying this until you get it set correctly. Only alter the Main Jet setting 1/8 turn at a time.You should also make sure that the Air Cleaner is really clean, you may need to remove it and wash it out. Leave it soaking in some Petrol or kerosene overnight, the following morning allow to drain thoroughly before re-fitting to the tractor and filling with engine oil up to the mark. Make sure that you only adjust the carburettor when the Engine is at working temperature, any less and it will change its tune when the temperature rises. To set the Slow running/idle jet, make sure that the Engine is idling below 450rpm or it will not run on the Idle Jet, it will be still running on the main jet. If you have any other questions about any of this, just email me direct...John(UK)[email protected]

Once again thank you John for your valued assistance and direction.
I will adjust the carburettor jet to lean out the mixture.
Your view that my carburettor may have larger jets is most likely correct as in the past I have had the main jet adjusted to 1 turn out for towing a small trailer around the property but was reluctant to leave it at this setting when working the tractor hard due to reading about the threat of damaging valves if left at this setting.
Will adjust this week end and let you know how I went.
Thank you once again.
Regards Brad

Question re: Air Breather Valve on Tea 20's

Brad V

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Charles in Aus.

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John(UK)

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Jerry/MT

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Brad V

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John(UK)

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Brad V

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