Ring step area lubrication and low/no oil consumption

[bulwnkl]

So, buster, you and the engineer don't think this is a self-correcting problem? I mean, if very low/no consumption leads to increased wear, then any such engine WILL shortly become an oil user and then last longer. So, the no-oil-burning engine still outlives the oil-burner because the no-burner is just as long-lived AFTER it starts burning oil as the oil burner was from the start.

 

[1sttruck]

"So, the no-oil-burning engine still outlives the oil-burner because the no-burner is just as long-lived AFTER it starts burning oil as the oil burner was from the start."

Unfortunately, probably not. The finish on the cylinders is important, and if they get worn and polished they won't work as well as ones with the proper finish. I guess the finish helps to hold and distribute some oil.

 

[lucky phil]

I'm an aircraft engineer by profession and an aircooled a/c piston engine is so far removed from a modern automotive engine the comparisons with regard to oil consumption and many other aspects are almost impossible to draw.
We had an old saying about Pratt& Whitney R1830 and 2000 engines.The only time you've got to worry about oil leaks is when you don't see any,It means its run out!
Ciao

 

[1sttruck]

There's apples, oranges, and I guess diesels are bananas. Mine uses some oil, more with higher loads, and it's typical. It's a 5.9L inline 6. Most seem to use some oil, which to me makes sense as one needs a bit of oil to minimize ring and cylinder wear. I guess one needs to consider load vs engine life, where the typical car in the US is expected to have a moderate life when used at lower load levels, while a diesel is typically expected to have a longer life at higher load levels.

 

[JohnBrowning]

I think that some oil consumption is always going to take place but some vechiles less so then others. My current Toyota does not consume enough oil dureing it's 6 month oil change intervals to even be discerned on the dipstick.

Some engine designs either due to the design or the materials selected consume a lot more oil then is needed for long life. I also think that we have seen how viscosity,base stock and additive packages all play a role in how much oil an engine consumes dureing the OCI!

I think that 1/2-1 quart of consumption dureing a 6 month OCI is more then enough for any production engine excludeing ultra high performance machines or air cooled machines.

Most oil consumption on modern engines is due to either the rings being to high on the pistons or cheap valve stem seals.

We all know that the low output 1.8L Toyota has used for a long time is prone to consuption. Same thing about almost ever engine GM builds and the older Ford modulars V8's etc......Seeing how their are TSB's for all of the most notorius oil burners from the bigger OEM's tell's us that is not proper to have excsesive oil consuption even if it is common place.

 

[Jimbo]

Even a "small" general aviation engine is huge compared to a motorcyle. The popular Lycoming O-360 has 360 cubic inches of displacement with only four cylinders, and it is a short-stroke design. When you account for thermal expansion, the clearances are quite large. A rebuilt cylinder barrel will we chromed, with dimpled pockets added to retain oil. The rings are plain iron. New cylinders are steel combined with chromed rings. These engines are far from modern auto or motorcyle technology. A quart of Aeroshell 100 (SAE 50) every five operating hours is indeed normal.

The 3350 cubic inch 18 cylinder engines used in the DC-7 could consume the 40 gallons of oil in the tank on a single long flight, such as New York to Paris.

 

[castor]

opposed corvair 4 ???

 

[bulwnkl]

Jimbo, when you say "chromed" (cylinders and rings), are you talking about what would be called 'hard chromed' in an agricultural context? The bright, shiny stuff that's super abrasion-resistant? If so, there was lots of hard chrome in the converted (to run on natural gas) 454 Chevys and industrial Cummins and turbo Cats I used to run for well pumps and generators. If it's hard chrome, that alone will make them use oil.

With the kinds of displacements, rpms, and power outputs being discussed, one wonders why a diesel engine-type construction would not work. Tractor engines work at above 80% output their whole lives and it's quite common for one to last in excess of 8,000 hours before a rebuild. They're warranted for 5,000 hours. They don't need hard chrome and they don't necessarily burn much oil. And yes, some are air cooled. See Deutz's wares.

 

[Blake Sobiloff]

bulwnkl, diesel engines are coming to general aviation, mostly because the leaded gas that is currently used may not be available forever. In fact, outside of North America 100LL is getting much harder to find and extremely expensive ($10/gallon).

Also, there's only one plant left in the world that makes the lead used in 100LL. It is based in Britain and the government there doesn't really like the product they produce, so there's concern that politics may disrupt the supply chain.

(This is all from a pretty good article at AVweb that discusses the "looming crisis.")

The thought is that a diesel would be an ideal alternative to current engines since it could run on Jet A, which is available everywhere. It would simplify distribution and refining. There's a good article at MachineDesign.com with an overview of the Diamond diesel airplanes being sold.

 

[1sttruck]

"...an aircooled a/c piston engine is so far removed from a modern automotive engine the comparisons with regard to oil consumption and many other aspects are almost impossible to draw."

The old air cooled opposed 4 VW engines seem similar, although with much lower power output. The opposed 4 and 6 Porsche engines seem similar, although they seem to be essentially air cooled. And GM's (answer to the Porsche ? :^), the opposed 4 Corvair seems similar. The v12 engines in cars seem to have much lower displacement than similar configurations in aircraft, and not many radials in cars either.

 

[Blake Sobiloff]

Lucky Phil, could you provide the highlights of the significant differences, or point us to a reference that does? I'd love to learn more. Thanks!

 

[427Z06]

quote:

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an aircooled a/c piston engine is so far removed from a modern automotive engine the comparisons with regard to oil consumption and many other aspects are almost impossible to draw.

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Finally. Someone with a clue.

 

[Curious Kid]

Not much for experience here but...

Aviation grade oil, 50 weight, is that the most commonly used weight and with such consumption? Anyone have temps of the oil in the sump in such cases?

I ponder the differences in duty cycles and sustained loading promoting thinning conditions of the oil about the pistons and rings resulting from elevated temperatures. I can't help to ponder the fact of large displacements and sweep area differences between aviation and the smaller everyday air cooled consumer units (auto/lawn and garden).

The note in the post made previously where there was a consumption difference with regular vs. synthetic, I wonder if the consumption had more/also to do with volitility than just oil passing control rings/stem seals.

 

[Steve S]

Piston rings are lubed by the oil in the cross hatch on the cylinder walls.