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Oil consumption realities

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mikenixon
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Oil consumption realities

#1

Post by mikenixon »

This late in powersports history, when new motorcycles have advanced so incredibly and technical knowledge has become so accessible, I often find myself surprised that riders still don't understand oil consumption, as demonstrated each time I am presented with the argument, common in many quarters, that since the spark plugs aren't oily and the exhaust isn't smoking, then oil consumption isn't happening. This unfortunately is fallacious thinking.

Certainly, how an engine is machined, either the first time or during a rebuild; that is, the quality of the fits and surface finishes resulting, play an important role in oil consumption. In rebuilt engines especially, the lingering (and malingering) adherence by many mechanics to a basically 1940s engine rebuild ethic, wherein clearances were large, cylinder wall finishes coarse, and the word "break-in" actually had meaning, is troublesome. This is not however the way Japanese motorcycle engines are made or how they are remade. 1 Much of the bike engine rebuild community is adrift in a storm of misinfomation and confusion resulting in bad rebuild practices. I deal with it constantly. Open-eyed observation of the design of Big Four engines and a little careful study of their service manuals promise real enlightenment. But you'll not find discussion of this on forums. One of the scandals that saddens me. 2

Obviously, all powersports engines consume oil, and the 50-year old ones we hold dear likely lead the way, for various reasons, not the least reason due to their rock-hard half-century-old valve guide seals. But new engines consume oil also, for reasons not yet considered. Because a telling piece of data and one of the unfortunate ways in which the powersports industry and the public are on different sides of a vast technical chasm 3, is that the Big Four in particular have historically "hedged their bets" for warranty purposes in regard to factory-approved levels of oil consumption, with the infamous "quart per thousand miles" policy. 4 This startling potential is no doubt present in only a random small number of mass-manufactured engines, certainly not many. And it happens by virtue of "tolerance stacking" during production. That is, the target spread of several interconnecting machined internal clearances sliding toward a sum total representing the extreme end of the acceptable range. And by establishing the 1000-mile reference the factory isn't saying they expect all their engines to be like that, only that they will accept the one in several hundred (or whatever the figure is) that might, because it is just too costly to establish manufacturing measures that would prevent its occasionally happening. 5 And hey, most of the production is to spec, and even the few out of spec are "to spec". They say so. -)

But this is not news. Much more importantly, and what you should know, is given the right combination of conditions, it is possible to make even a well-manufactured and well-maintained engine use oil excessively. Because the above-mentioned cases are not the only, or even the greatest, sources of oil consumption. The most significant source of oil consumption in powersports engines is and has been as long as most of us can remember, oil vaporization. Vaporization, that is, the oil frothing and misting and exiting the crankcase as an ether, goes on in all engines no matter their size, type, wear or condition. But none can compare with the phenomenon in the powersports industry's relatively small engines, whose power is necessarily developed at large throttle openings and whose crankcases hold surprisingly small volumes of oil to begin with. 6 So critical in these engines is oil vaporization that motorcycle motor oil developers take pains to rate the vaporization characteristics of their products, something car motor oil technical people don't even think to do. And so dramatic are the possibilities that there are documented cases of brand new single-cylinder and twin-cylinder Hondas virtually running out of oil at the end of a single, long-distance sustained high-speed run. Think Barstow to Vegas. The oil was not burned; it did not appear at either exhaust or spark plug. It simply disappeared. Consequently, I have for most of my career warned the owners, particularly those of smaller bikes, to watch their oil levels closely. But even larger motorcycle engines such as the peculiarly hot-running CBX1000 are observed to vaporize their oil noticably. Oil vaporization is something every rider must keep in mind.

1 This is the biggest problem in the powersports engine repair industry, this fixation on rebuild techniques outdated generations ago, and some that were never legitimate in the first place. There is no such thing as "break-in" of a properly assembled Japanese engine's top end, either at original manufacture or remanufacture. The valves are sealing their best before the engine is ever started, and the rings follow immediately after, by the time the first test-ride is completed.

2 Forums unfortunately universally perpetuate bad rebuild practices.

3 Not just a chasm, but veritable galaxies that place them in different edges of the motoring universe.

4 And some Euro OEMs prescribe to half that, i.e. a quart in 500 miles.

5 In other words, the cost difference between knowing one in several hundred will be almost out of spec and one in several thousand will be is exponential-- it isn't simply spending five percent more in production. As with many things, the cost graph curves upward steeply for only tiny improvements in production processes.

6 High rpm whips the oil more and smaller volumes heat it more.
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Re: Oil consumption realities

#2

Post by 77Gowing »

Dare I even comment.
1. I have understood that any recipicating engine consumes oil. If it didnt, it would burn up through friction. And, it stands to reason since the bore of "the bowl" is wet with oil and some always gets past the rings, not to mention the potential for leak by with the valve seals.
Indeed when analyzing particulate emmissions some of the particulates can be referred to or classified as wet and dry particulates. With the "wet" being contributed via the lubricating oil. And the dry being contributed by the fuel (unburned that is). At least in the diesel combustion analysis world.
I speak out of turn here but only from personal observation. I haven't much in the way of credentials.
"Vaporization, that is, the oil frothing and misting and exiting the crankcase as an ether, goes on in all engines no matter their size, type, wear or condition." Very interesting and I note the smaller volume of oil will have a smaller heat capacity.
Side comment: few realize that the lubrication system is actually part of the cooling of an engine. Without lubrication, friction is obviously high and things will burn up & wear out. Reduce friction and you reduce heat.

Great article Mike as always. I enjoyed the read. It has been too long since I worked with my combustion colleagues, of who's shoes I was un worthy to tie. But I miss the technical learning environment I used to work in with such capable people to learn from.
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Re: Oil consumption realities

#3

Post by mikenixon »

:)

Yes. The fuel comes into play for cooling also, on some engines more than on others. About the CBX1000 I like to say it is a liquid-cooled engine; the liquid happens to be fuel.
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Re: Oil consumption realities

#4

Post by Track T 2411 »

Another good read, Mike. Might one assume that vaporization is the major cause of the common Goldwing engine trait of 'losing' that initial 1/4 to 1/2 quart of oil right after an oil change if the crankcase is filled to the actual 'fill' line? There's been a few discussions about that...
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Re: Oil consumption realities

#5

Post by mikenixon »

Not having owned a Wing myself I have not experienced that. And none of my customers have ever shared that issue with me.
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Re: Oil consumption realities

#6

Post by 5speed »

you want some "light reading" on oil consumption in brand new automotive engines?
google GM 5.3 liter oil consumption, make some pop corn and enjoy..
they are well known to consume a quart/ liter of oil every 5000 miles.
my 08 sierra goes thru at least a liter between oil changes..more if I'm working the truck hard.
I am pretty anal about checking the level of the oil in all my gas powered vehicles, toys,etc.
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Re: Oil consumption realities

#7

Post by rcmatt007 »

mikenixon wrote: Wed Jan 13, 2021 6:22 pm Not having owned a Wing myself I have not experienced that. And none of my customers have ever shared that issue with me.
this has come up several times at least on this forum. It appears that it is common, if filled to the top of the line" to loose about 1/2 quart. Might just be that it goes out the left side from being parked on the side stand
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Re: Oil consumption realities

#8

Post by mikenixon »

Interesting. Not being argumentative, just, in almost 50 years with these bikes, never heard of it.
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Re: Oil consumption realities

#9

Post by rcmatt007 »

I don't recall it doing that when my 78 was new.... valve guide seals never get hard do they anim-cheers1
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Re: Oil consumption realities

#10

Post by mikenixon »

:)
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Re: Oil consumption realities

#11

Post by mikenixon »

Not really related, because it is about fuel consumption not oil consumption, but an interesting experience. I disassembled an engine this week. The owner complained of high fuel consumption. It's a Honda 550 four and the bike shows 53,000 miles. When the cylinder was removed all four top rings fell out in pieces, and there are nicks in the bottom edges of the cylinder sleeves. The rings are original as shown by their being worn almost in half thickness-wise. Literally. And the pistons show a lot of blowby, likely also 53,000-mile parts. Yet, with all of this the cylinders measure as-new clearance and taper and out-of-round, the valves show minimal use, no recession, and the guides as-new. The scenario shapes up this way: the previous person purchased a new NOS cylinder assembly and a new NOS cylinder head, installed them with new gaskets, and left the pistons and rings as-is. Pretty amazing. An interesting combination, don't you think? Not something you see very often.
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