Lycoming cam wear power loss

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Dan Thomas

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If you starter crank an engine occasionally with no ignition or no fuel it should splash lubricate the cam without introducing blow by moisture.
Not enough centrifugal force at those speeds. And at cranking speed there's almost no oil pressure anyway to supply the crank with oil.
 

Dan Thomas

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Cars have some form of positive crank case ventilation since the 60s. It makes the rings work better so there is less blow by, the engine consumes some of the bad vapors, the oil stays cleaner longer; lots of wins. Except, standard auto pcv needs part throttle vacuum to work, so you have to hook an airplane up like a race car to the exhaust. The bad part comes if the one way valve carbons up and sucks all the oil out. It does it fast. You just introduced something that can help but hurt too. You have to keep on top of it.
For ground, You can make up desiccant packs. You have a hose that slips on the breather and oil fill running to a big pack and try to suck moisture out while parked. The minute you stop an engine, relatively cool air going up the breather tube makes it “rain” in the engine. Pretty much sticks wherever it was last.
PCV doesn't make the rings work better. The liquid-cooled engine, by nature, has lower operating temperatures. and so the engine can be built with much smaller clearances. That alone reduces blowby.

And like I said, you can't suck enough moist air into the engine to get significant water.

1623978544115.png

At 60°F, the air will hold no more than 10.7 grams of water per kilogram of air. How big is a Kg? At standard temp (59°F) at sea level it's 28.7 cubic feet, or a bit more than a cubic yard. 10.7 grams is a bit more than a third of an ounce, about two teaspoonfuls. The inside of a crankcase, full of all the stuff I mentioned earlier, is less than a cubic foot. Take a look inside one someday when a cylinder is off it. A cubic foot of saturated air at 60°F will hold no more than 0.37 grams of water, which is a few drops. Now, consider that the temperature swing required to get those few entire drops of water into the crankcase, if it was pretty much foggy outside, would have to be from ambient to absolute zero, and ALL the water would have to stay in there when it warmed up again. We never see swings like that, of course; it's only a tiny fraction of that, so very little air is going into and out of the crankcase during normal temp swings, even after shutting down a hot engine in cool air. And when the air leaves it takes some of the water with it.

So many are worried about their coastal environment, and then go and run up the engine to circulate the oil to make the engine last longer. It's crazy. A gallon of gasoline generates a gallon and a half of water simply by combining hydrogen from the gasoline with oxygen from the air. That's a LOT of water, and some of it is getting past those rings in a cold engine. It condenses in there and some of it runs down under the oil in the sump, and no amount of dessicant or warm air blown through the case is going to get at it. I've seen sumps rotted out from that.
 

Dana

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Not to mention that the condensed water then mixes with oil and combustion by-products, making an acidic mixture that's even more corrosive than plain water.

I'm building an oil separator for my crankcase breather. I'm still considering whether to pipe the condensed oil back to the crankcase or just collect it and drain it periodically, I've heard good arguments for both. I get a fair amount of water in the current puke bottle, but the breather hose just ends in a can low on the firewall in the airflow. The new separator will be higher on the firewall in a warmer place, hopefully less water will condense out.
 

Dan Thomas

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Not to mention that the condensed water then mixes with oil and combustion by-products, making an acidic mixture that's even more corrosive than plain water.

I'm building an oil separator for my crankcase breather. I'm still considering whether to pipe the condensed oil back to the crankcase or just collect it and drain it periodically, I've heard good arguments for both. I get a fair amount of water in the current puke bottle, but the breather hose just ends in a can low on the firewall in the airflow. The new separator will be higher on the firewall in a warmer place, hopefully less water will condense out.
There are concerns elsewhere that the Airwolf STC'd oil separators that get most of the oil out of the breather exhaust are hurting the engines they're on. The also get the water and water vapor that's leaving and sending it back to the crankcase along with the oil. Totally counterproductive. Much worse in colder weather, since the separator will also be cooling the outflow and condensing more vapor. We had one on a 172, and the ICA specifies a disassembly and cleaning every 100 hours, something of a pain. I took it off and didn't see much difference in the amount of oil on the belly.
 

BBerson

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Not enough centrifugal force at those speeds. And at cranking speed there's almost no oil pressure anyway to supply the crank with oil.
I don't know if oil pressure helps spray the cam lobes or not. If no oil gets on the lobes while cranking isn't that a problem?
 

TFF

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I have to disagree on the rings. Only since the mid 80s did manufacturers take advantage of low tension rings. Before that there was not too much difference in rings depending on chrome or not. I got chrome rings in one of my Alfas. The full advantage might not be there like water cooled, but it does help. It helps on one friend’s RV until the valve clogged. He wasn’t cleaning it as often as he should. It has less oil consumption than without by more than a quart and the belly is a lot cleaner. All assuming the valve is taken care of.
 

dog

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You are missing what I said about this being airplanes that had just been pulled out and run up prior to inspection and oil change? That's when most water gets into a crankcase: when it's being run up from ambient temperatures. Clearances are larger so blowby is much worse.

I had said:

I have taken the cylinders off an engine that has just been run up (from cold) for oil change and differential compression testing. The filter shows aluminum chips, maybe, a sign that the piston pin plugs are being shaved by the lower ring ridge in the cylinder, or maybe the compressions show a leaking valve. Anyway, there are water droplets between the piston and cylinder and sometimes quite a lot of water in the rocker boxes. This was in engines at a flight school, run hard almost every day. Hangared every night.

I mentioned that "they were run hard almost every day and hangared every night" so that nobody could say that it was condensation from the atmosphere in the engine. I have taken cylinders off airplanes that have come back from long flights and found no water anywhere at all.

Clear now?
Less Foggy.
So you have been adamant that a short run up is the worst thing that can be done to an engine.
I am trying to understand all the different proceses, and what occurs to me is that one
of the largest components of exhaust gas is water vapor,which we have all seen dripping out of the tail pipes of well tuned cars under certain conditions.
So during a short run up of a cold engine,the
vapor content of the exaust gas in the blow by
is sufficient to create liquid water between the
rings and condence in the crank case into noticable droplets.
The example sited of a run up prior to a differential compression test vs long flights
suggests that the rings/piston clearances
change from cold to hot enough to reduce blow by and the resultant water hugely,and the reason we dont see a CLOUD of vapor and smoke on start up is that it is condensing in our engine cases into cam rotting goo.
I dont know the numbers but I suspect that the
water produced by burning a gallon of av gas is
going to be at least one eighth of that.
 

Dana

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The vast majority of the water produced by combustion goes out the exhaust. You see water dripping out of a car exhaust when the engine is first started and exhaust system is still cold enough to condense a lot of that water vapor; add to that all the moisture that condensed in the muffler when the engine was last shut down. Once it’s hot, the vapor passes through the system without condensing. It’s the same with blowby; it will condense in the crankcase of a cold engine, but once it’s warmed up most of it will pass harmlessly out the breather. And yes, there will be considerably more blowby until the piston heats up and the clearances decrease.

You don’t see that vapor cloud when an aircraft engine starts up because the exhaust is much shorter and heats up faster, and mostly points down so the water can drain out after shutdown. Also the prop blast blowing past the exhaust probably spreads it out too thin to see.

Regarding the oil separator, if it’s maintained at a high enough temperature to keep the water from condensing out, all or most of the vapor should pass out of the separator’s vent and only dry oil will be collected. At least, that’s the theory. I’m going to install the separator, and initially not plumb it to drain back into the engine. When I see what I’m collecting, I’ll decide whether it’s advisable to return the collected oil to the engine. Either way, it should reduce the oil on the belly compared to the open can the breather goes into now. I built a similar separator for the Mosler engine on my Fisher 404 and it made a huge difference. On that one I used the return line since the acceptable oil level range was very narrow.
 

BBerson

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If the engine was started and run for only 15-30 seconds each month that would coat the cam with oil. I don't think enough blow by would condense or harm a fresh oiled cam in 15 seconds.
Might need to be lab tested.
I read the Continental A65 manual which a ridiculous storage process. And needs a redo after 30 days!
 

TFF

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I think the real issue is you get startup wear without ever getting use out of it. Might prevent some rust but engines don’t wear much once warm and running. Almost all the wear is cold starts.
 

Dan Thomas

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You don’t see that vapor cloud when an aircraft engine starts up because the exhaust is much shorter and heats up faster, and mostly points down so the water can drain out after shutdown. Also the prop blast blowing past the exhaust probably spreads it out too thin to see.
I often saw the fog behind an aircraft exhaust when on approach at -20°C in the flight school. At low power or idle, the exhaust gets cold enough and the prop slipstream is minimal, and that moisture condenses and leaves a trail behind the airplane.
 

proppastie

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when I decide not to post something after I have written it I have to do this.......delete....it would be nice to have a cancel button instead.
 

Dan Thomas

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I dont know the numbers but I suspect that the
water produced by burning a gallon of av gas is
going to be at least one eighth of that.
Believe what you want.

Molecular weights of the representative octane combustion are C8H18 114, O2 32, CO2 44, H2O 18; therefore 1 kg of fuel reacts with 3.51 kg of oxygen to produce 3.09 kg of carbon dioxide and 1.42 kg of water.

From Gasoline - Wikipedia
 

Dan Thomas

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I don't know if oil pressure helps spray the cam lobes or not. If no oil gets on the lobes while cranking isn't that a problem?
Oil pressure doesn't spray the cam lobes. The only oil during startup is what was left on them that didn't drip off. Additives such as Camguard can help with that, as can the additive in Aeroshell 15W50. Remember that the oil film only has to be thick enough to prevent metal-to-metal contact, and a few molecules thick is enough for that for a few cycles until the oil gets thrown around after startup.

Lycoming started using roller lifters about 15 years ago, and they convert the old crankcases to take the new lifters during overhaul. It was their answer to the scuffing problem. There are some STC'd solutions, one of which is an aftermarket camshaft that is rifle-drilled to take oil under pressure from its bearings out to the lobes, where it is squirted out small holes just at the root of the lobe.
 

Dan Thomas

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If the engine was started and run for only 15-30 seconds each month that would coat the cam with oil. I don't think enough blow by would condense or harm a fresh oiled cam in 15 seconds.
Might need to be lab tested.

Don't be alarmed by that picture of a rusty cylinder. It was obviously sprayed with salt water after it was cut. Look at the cut surfaces and the flow pattern left in the rust.

Pay attention to what he says starting at 3:39.

Any combustion water vapor getting past the rings is detrimental to that engine and any short run will do more damage than good.
 

dog

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Believe what you want.

Molecular weights of the representative octane combustion are C8H18 114, O2 32, CO2 44, H2O 18; therefore 1 kg of fuel reacts with 3.51 kg of oxygen to produce 3.09 kg of carbon dioxide and 1.42 kg of water.

From Gasoline - Wikipedia
Hey Thanks,looked for that.And wow thats a lot
of water.
All the talk of cam damage has me concerned
for my A-65 sitting there waiting,and have
pulled out a spare cam,which the overhaul
manual specification is that if it looks good it is,the only measurements to check is the journal bearing ,and lift .4”,no four places after the decimal stuff.
I think I will construct a ramshackle analogy of
ICE just bieng underperforming hydrogen technology with bad breath.
 

TiPi

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Oil pressure doesn't spray the cam lobes. The only oil during startup is what was left on them that didn't drip off. Additives such as Camguard can help with that, as can the additive in Aeroshell 15W50. Remember that the oil film only has to be thick enough to prevent metal-to-metal contact, and a few molecules thick is enough for that for a few cycles until the oil gets thrown around after startup.

Lycoming started using roller lifters about 15 years ago, and they convert the old crankcases to take the new lifters during overhaul. It was their answer to the scuffing problem. There are some STC'd solutions, one of which is an aftermarket camshaft that is rifle-drilled to take oil under pressure from its bearings out to the lobes, where it is squirted out small holes just at the root of the lobe.
Cam lobe-follower (lifter) lubrication only works when there is oil AND relative movement between the two at a minimum speed. Cranking or turning the engine by hand does not create enough speed between the 2 surfaces to build the hydrodynamic film (oil film). At these very low speeds, the pressure of the valve spring will overcome the oil film and the contact will be metal to metal (eg boundary lubrication). It is the same concept as for the plain bearings, the oil film separating the crankshaft from the bearing surface requires an oil supply and a minimum circumferential speed to create and maintain the oil film.
The ZDDP and other additives reduce the friction (and damage) at start-up but can't prevent some metal to metal contact.
For more info, check out this: Lubrication Regimes Explained
 

BBerson

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I didn't see what the minimum cranking rpm was for hydrodynamic pressure?
Or if hydrodynamic pressure happens on open cam lobes?
 
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