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Thread: Automotive piston rings in Lycomings

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    Registered User 7shannon's Avatar
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    Automotive piston rings in Lycomings

    I have heard of guys using automotive piston rings in Lycomings and continentals, I have a O235 C1 I got for cheap that needs torn down and inspected, and since I am experimental I dont want to pay the huge cost for certified parts, does anyone have part numbers for the automotive rings that will fit the O235 pistons?
    Thanks, Kevin

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    Registered User Toobuilder's Avatar
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    Re: Automotive piston rings in Lycomings

    The little Continentals use common piston diameters with automotive applications, so plenty of people will use gapless rings in racing applications. However, the diameter of Lycoming pistons is well outside automotive applications, so that is going to be your first hurdle.

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    Registered User SVSUSteve's Avatar
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    Re: Automotive piston rings in Lycomings

    My thought is if you're willing to use automotive parts in a hodge-podge fashion (mixing automotive and aviation engine parts), why not just break down and switch to an automotive conversion? I could be wrong but that would be my thinking.
    "Unfortunately in science what you believe is irrelevant."- Orion

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    Moderator Dana's Avatar
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    Re: Automotive piston rings in Lycomings

    Steve, the idea is that specific auto parts are cheaper and functionally equivalent, while the aero engine as a whole is more suited to aircraft use than a converted car engine that was never designed for the aircraft duty cycle (cooling and lubrication in particular).

    -Dana

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    Registered User SVSUSteve's Avatar
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    Re: Automotive piston rings in Lycomings

    Steve, the idea is that specific auto parts are cheaper and functionally equivalent, while the aero engine as a whole is more suited to aircraft use than a converted car engine that was never designed for the aircraft duty cycle (cooling and lubrication in particular).
    I get that. My point being that if the engine is not designed to take it, then it would follow (at least from a basic logical standpoint) that the parts thereof are not designed to take it. I'm not an "engine guy" obviously, but isn't one of the major reasons for piston ring failures is overheating and/or inadequate lubrication. Going with something that isn't designed for the particular use, be it a part or a whole engine, is a potential problem and should not be taken lightly....
    "Unfortunately in science what you believe is irrelevant."- Orion

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    Moderator Dana's Avatar
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    Re: Automotive piston rings in Lycomings

    Yes, but the the lack of cooling or lubrication isn't caused by the piston ring but the other engine components. Many aircraft and aircraft engine manufacturers have used automotive components where appropriate, particularly in years past. I know the original gascolator in my T-Craft was a International Harvester tractor part. Take a Ford piston ring and put it in a box labeled "Continental" and charge 4X the price... such a deal! Basic things like bearings or piston rings don't know what they're installed in. And in many cases, advances in metallurgy mean the modern automotive part may be better than the still-made-to-the-1939-spec "aircraft" part, which really may be just a 1939 car part.

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    SVSUSteve and delta like this.

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    Registered User 4trade's Avatar
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    Re: Automotive piston rings in Lycomings

    541 Chrysler stroker have same bore than std O 235. Couple of things to check before start to play with these ones. Check carefully ring gap clearance, it must be with manufacturers limits, or it will destroy your pistons fast, second one, check those automotive piston rings pressure (against cylinder wall). If automotive rings have much higher pressure against cylinder wall, it might destroy your cylinders quick....otherwise i donīt see much problem to use automotive stuff here.
    Mantraīs like: " it is too difficult" or "it is impossible" is true only for those people who use it...

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    Registered User Toobuilder's Avatar
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    Re: Automotive piston rings in Lycomings

    +1 Dana. In many cases, "aircraft" parts are in fact repackaged automotive or industrial parts. Beware the myth that all aircraft parts are "engineered" for that duty cycle... In many cases, they were simply the cheapest parts around. As for piston rings in aircraft engines, keep in mind they must be compatable with the cylinder wall. The gapless rings used in the Continentals is a trick used in Formula 1, where the cylinders are bored to their maximum dimension, but NOT chromed. If you have chrome cylinders, that takes a different type of ring material.

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    Registered User Dan Thomas's Avatar
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    Re: Automotive piston rings in Lycomings

    Quote Originally Posted by 4trade View Post
    541 Chrysler stroker have same bore than std O 235. Couple of things to check before start to play with these ones. Check carefully ring gap clearance, it must be with manufacturers limits, or it will destroy your pistons fast, second one, check those automotive piston rings pressure (against cylinder wall). If automotive rings have much higher pressure against cylinder wall, it might destroy your cylinders quick....otherwise i donīt see much problem to use automotive stuff here.
    I have experience with this. In order to "save" money when I rebuilt the A-65 for my Jodel, I used piston rings intended for International Harvester trucks. Same cylinder diameter, same ring thickness. But, here's the bad part: those rings were stiffer, either because they were a hair wider (between the O.D. and I.D.) or because the material (cast iron) had more carbon or had been heat-treated differently, and the rings wore six or eight thousandths out of the cylinders in about 50 hours. Trashed them. Those cylinders are 4130 steel, folks, and the International rings were intended for cast iron cylinders in a cast block. Cast is considerably harder than steel, and a liquid-cooled automotive cylinder block doesn't get nearly as hot as the aircooled steel cylinders of an aircraft engine.

    I won't do that again. Old guys had told me that certain rings were the same as aircraft rings, and they were wrong. Size is only part of it. Sure, I saved maybe $100, and lost four cylinder assembles worth $4500. Big savings, huh?

    Dan

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    Registered User 4trade's Avatar
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    Re: Automotive piston rings in Lycomings

    Dan is right at this one, rings need to be always softer material too, than cylinder, or it will "eat" cylinder walls.
    Mantraīs like: " it is too difficult" or "it is impossible" is true only for those people who use it...

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    Registered User SVSUSteve's Avatar
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    Re: Automotive piston rings in Lycomings

    Quote Originally Posted by Dana View Post
    Yes, but the the lack of cooling or lubrication isn't caused by the piston ring but the other engine components. Many aircraft and aircraft engine manufacturers have used automotive components where appropriate, particularly in years past. I know the original gascolator in my T-Craft was a International Harvester tractor part. Take a Ford piston ring and put it in a box labeled "Continental" and charge 4X the price... such a deal! Basic things like bearings or piston rings don't know what they're installed in. And in many cases, advances in metallurgy mean the modern automotive part may be better than the still-made-to-the-1939-spec "aircraft" part, which really may be just a 1939 car part.
    Thanks for the explanation. I appreciate it since I am still learning about engines.
    "Unfortunately in science what you believe is irrelevant."- Orion

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    Re: Automotive piston rings in Lycomings

    Well I am not that well versed on aircraft engines, however I have flown behind some and I have some experience with engines.

    If the Lycoming engine is anything like the one in the Jabiru I fly, they are intentionally set up to burn some oil, or at least it appears that way as I almost always have to add oil when I check it out for my pre-flight. I ask the mechanic about it and it was his opinion that the engine design is such the oil is needed to lube and cool the cylinders.

    So some of the problem with using auto rings in an air cooled aircraft engine may have to do with the fact that auto engines are designed not to burn oil and keep it all in the oil pan.

    A way around this problem (not enough oil lube in the cylinder) would be to weaken the oil scraper ring so some oil gets by. A friend of mine who raced a Formula car with a 1600cc four cycle four cylinder engine used to deliberate weaken the oil scraper ring to get more top end lubrication. Claimed it increased HP. Don’t know if it did or not, but there always a little smoke coming out of his exhaust pipe. Most of his competitors would look at that and think the engine was ready to blow, but it always keep running.

    Richard

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    Registered User 4trade's Avatar
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    Re: Automotive piston rings in Lycomings

    If the Lycoming engine is anything like the one in the Jabiru I fly, they are intentionally set up to burn some oil, or at least it appears that way as I almost always have to add oil when I check it out for my pre-flight. I ask the mechanic about it and it was his opinion that the engine design is such the oil is needed to lube and cool the cylinders.

    So some of the problem with using auto rings in an air cooled aircraft engine may have to do with the fact that auto engines are designed not to burn oil and keep it all in the oil pan.
    Continental O 200 pistons have oil hole bore between compression ring/ oil rings. That small hole will supply oil between rings and this is why aircraft engines are so (oil) thirsty. This is old relic for time when oil quality was considerably lower than today, some kind of cheap insurance to add lifetime and reliably of engine.

    We have much better alloys for piston material, better oil quality and modern hi comp aircraft aftermarket pistons are like automotive ones, without extra oil holes than original. Oil between rings have only one purpose, lubricate cylinder walls. There is no other purpose, like cooling cylinder walls. Thin oil mist inside of engine is all you need to lubricate properly cylinder walls and excessive oil supply donīt give any real benefits.
    Mantraīs like: " it is too difficult" or "it is impossible" is true only for those people who use it...

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    Re: Automotive piston rings in Lycomings

    I have a gut feeling that some smart guys at Lycoming and Continental might disagree with you...?

    It's worth noting that high compression after market cylinders can also cut deeply into your TBO (for Lycoming's anyway), especially for an experimental engine that has a "real TBO" on-condition which is normally many hundred of hours longer than the stated factory TBO, with correct engine care.

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    Registered User Dan Thomas's Avatar
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    Re: Automotive piston rings in Lycomings

    Quote Originally Posted by Richard6 View Post
    A way around this problem (not enough oil lube in the cylinder) would be to weaken the oil scraper ring so some oil gets by. A friend of mine who raced a Formula car with a 1600cc four cycle four cylinder engine used to deliberate weaken the oil scraper ring to get more top end lubrication. Claimed it increased HP. Don’t know if it did or not, but there always a little smoke coming out of his exhaust pipe. Most of his competitors would look at that and think the engine was ready to blow, but it always keep running.

    Richard
    The cylinder and pistons and rings need very, very little oil compared to the rest of the engine, and in most applications they get far too much. Oil shot into the bottom of the piston by holes in con rod caps, for instance, is for cooling, not lubrication.

    Oil rings can only control so much oil. If too much is flung into the cylinder, the rings begin to hydroplane on it and oil consumption goes way up, along with the spark plug fouling and valve stem coking and sticking that comes with burning oil. The risk of destructive detonation also goes way up when oil is part of the combustion process.

    I spent 12 years in the compressor rebuilding business. Oil control is critical in air compressors, since it will contaminate the whole air brake system with sticky varnish and will cause serious coking and clogging of the discharge passages in the cylinder head. Since there is no combustion happening in there, any oil getting past the rings causes serious trouble. I found that by sticking closely to the manufacturer's bearing clearance specifications I could keep the oil pumping troubles to almost nothing, and warranty claims for oil pumping dropped right down to nothing.

    The trick is to keep those clearances very close so that much less oil escapes the bearings to be flung into the cylinder. The crosshatch in the cylinder wall, as microscopic as it is, holds enough oil for piston and ring lube and will not release the oil into the combustion process (in the engine) or into pumped air (in the compressor). The cooler cylinder wall prevents most of the very thin bit of oil from being boiled off.

    If the compressor suffered an oil-supply failure, the bearings always failed first, long before the pistons or rings ever seized.

    So we need to reduce the amount of oil getting past the rings, not increase it. We don't need much. Aircraft engines will use more oil not because they're dinosaurs but because they're air cooled, and so their temperature range is much larger than a liquid-cooled engine, so the clearances must be larger. Ring gaps and piston-to-cylinder clearances in the Lyc or Continental will be bigger than in your typical Toyota, for sure, and it will use more oil than the Toyota. Yet, when I replaced the Lycs in the fleet, i always followed to the letter the break-in procedures provided by Lycoming and we seldom had to add oil between 50-hour inspections. Many guys will baby a new or overhauled engine, exactly the wrong thing to do, and it will use far too much oil. That engine need high pressures and temperatures to get the rings and cylinders to seat properly, a nice way of saying that they must grind away at each other until they mate closely. Babying it results in the rings riding on high spots that get glazed and shiny and hard, leaving gaps where the cylinder has low spots, so that oil sneaks past the rings and gets into the combustion chamber. The wear stops once the glazing happens and the engine forever after uses oil. It's not, as I say, an old-technology problem; it's an engine-operation problem.

    Dan
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