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Old Jul 16, 2008, 02:15 AM
Beaver Boy
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Why so much oil?

I've been pondering this for a while now. Why do glow engines use such a high amount of oil? I mean, if you look at a 2-stroke bike engine, or even a lawnmower, they obviously run petrol/gasoline, but only a very small amount of oil (eg, 2%) and they seem just fine.. (although higher quality oils do make more noticeable improvements to wear etc)..

I've noticed that even the petrol model plane engines still run more oil than their motorbike/garden_device counterparts, even of a very similiar design and displacement..

Can anyone shed any scientific light on this?
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Old Jul 16, 2008, 02:56 AM
The reviewer
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Tokoroa
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There are two reasons why glow engines need so much oil:

1. the conrod journals on our little engines are only bushed, they don't have roller bearings like larger engines do. A roller-bearing can operate with incredibly low oil percentages because the vast majority of the motion is rolling not sliding. A bushed journal bearing is a form of hydrodynamic bearing and that requires enough oil to provide a film that will keep the two metal parts (the journal and the shaft it rides on) from touching -- this requires *more* oil.

2. the oils that most US fuel-makers use are pretty low-tech and "cheap". The vast majority of the synthetics found in US fuels are PAG-based (a close relative to anti-freeze). Better oils (namely carefully formulated Ester-based synthetics) *can* be used at lower percentages than the PAG-based oils from Morgans or Klotz. When I can get it, I run oil from Cooper Fuels at 12% by volume and this oil is so good that you can even go to 8% if you're careful with your tuning. Europeans have known about these hi-quality ester-synthetics for a long time and there is a much wider choice over there where the likes of Motul Micro, Aerosynth and Aerosave offer the same kind of low-percentage protection.

So why do US companies persist with less-sophisticated oils that have to be used in higher volumes to provide the same protection? Well I guess because they're cheaper to make they have a higher profit margin and because you need more to do the same job, the sell more and their profits are even higher again.
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Old Jul 16, 2008, 02:59 AM
engine-a-holic
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Scientific answer: the big and upper ends of the conrod are plain bushed. Gas engines have needle bearings there. Less friction, less lubrication needs, less wear and metal fatigue
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Last edited by Patxipt; Jul 16, 2008 at 03:04 AM. Reason: XJet beat me to it
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Old Jul 16, 2008, 06:36 AM
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Xjet, what do you suppose the oils you've been using are? They surely aren't manufactured for the hobby industry. For a high quality synthetic the price Cooper's charge per gallon is very reasonable. So what industry are they coming from? Also, Castor is a good model engine lubricant, why isn't it used at 8-12%?

I've just started running 8% castor in my Enya 46-46 with ignition. We'll see how it does. Peter Chinn's four stroke book suggests that this is perfectly acceptable.
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Old Jul 16, 2008, 11:25 AM
Gentle 'Bella'
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rc_sjo -

I'm not sure what scientific explanation you're wanting.

There would be two areas I can name: engineering and molecular. Since this is a hobby industry and gets most of it's principles from general sources, I'm sure there are factors even the manufacturers don't know. In the case of lubricants, I think they have settled on a fail-safe formula, maybe by trial and error, that modelers can have protection for their motors to cover mistakes and errors in operation towards success and enjoyment.

You'll find that there are a number of modelers that have experimented and found that they indeed need less oil than the usual 20% or so found in commercially available fuel but certainly at their own risk. Trial and error.
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Old Jul 16, 2008, 01:59 PM
Ignint McNugget
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Brother XJet - do you mean to say PEG (polyethylene glycol) where you've written PAG? If not, what does PAG stand for?
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Old Jul 16, 2008, 02:26 PM
And You're Not
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Quote:
Originally Posted by XJet
So why do US companies persist with less-sophisticated oils that have to be used in higher volumes to provide the same protection? Well I guess because they're cheaper to make they have a higher profit margin and because you need more to do the same job, the sell more and their profits are even higher again.
What country is Cooper's from?
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Old Jul 16, 2008, 05:04 PM
The reviewer
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Tokoroa
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Quote:
Originally Posted by Rumple
Brother XJet - do you mean to say PEG (polyethylene glycol) where you've written PAG? If not, what does PAG stand for?
PAG = Polyalkylene Glycol
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Old Jul 16, 2008, 05:05 PM
The reviewer
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Tokoroa
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Quote:
Originally Posted by Jeffery
What country is Cooper's from?
It's from the USA Cooper Fuels
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Old Jul 16, 2008, 05:09 PM
The reviewer
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Tokoroa
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Quote:
Originally Posted by gkamysz
Xjet, what do you suppose the oils you've been using are? They surely aren't manufactured for the hobby industry. For a high quality synthetic the price Cooper's charge per gallon is very reasonable. So what industry are they coming from?
The basic components are used in a wide range of industries where non-petro lubes are required. The secret is choosing the most suitable base-stocks and blending them with a good additive package to provide maximum performance in the rather unique environment of our model engines.

Quote:
Also, Castor is a good model engine lubricant, why isn't it used at 8-12%?
While it is a good lubricant (especially compared to some of the low-tech synthetics) it also has some deficiencies. I wouldn't use with methanol at 8% in a model engine.

Quote:
I've just started running 8% castor in my Enya 46-46 with ignition. We'll see how it does. Peter Chinn's four stroke book suggests that this is perfectly acceptable.
Is your Enya 46 a 4-stroke?
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Old Jul 16, 2008, 06:54 PM
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Xjet, yes that was supposed to read Enya 46-4C.

Fuchs (Aerosynth/save) or Motul would be able to formulate a model specific lubricant. I'm not sure how anyone else would be able to do that.

The others I'm guessing are repackaged products.

Greg
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Old Jul 16, 2008, 07:15 PM
The reviewer
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Tokoroa
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Quote:
Originally Posted by gkamysz
Xjet, yes that was supposed to read Enya 46-4C.

Fuchs (Aerosynth/save) or Motul would be able to formulate a model specific lubricant. I'm not sure how anyone else would be able to do that.

The others I'm guessing are repackaged products.
I know that Coopers formulate their own oil and additive package.
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Old Jul 16, 2008, 08:12 PM
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Too bad he has no information about it on his website.
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Old Jul 16, 2008, 09:54 PM
The reviewer
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Tokoroa
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Quote:
Originally Posted by gkamysz
Too bad he has no information about it on his website.
Just drop him an email.

There aren't a lot of home-brewers in the USA so his site focuses mainly on ready-mixed fuel. He'll sell the oils on request.
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Old Jul 17, 2008, 02:03 AM
Registered User
Australia, NSW, Attunga
Joined Dec 2006
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Quote:
Originally Posted by rc_sjo
I've been pondering this for a while now. Why do glow engines use such a high amount of oil? I mean, if you look at a 2-stroke bike engine, or even a lawnmower, they obviously run petrol/gasoline, but only a very small amount of oil (eg, 2%) and they seem just fine.. (although higher quality oils do make more noticeable improvements to wear etc)..

I've noticed that even the petrol model plane engines still run more oil than their motorbike/garden_device counterparts, even of a very similiar design and displacement..

Can anyone shed any scientific light on this?

G'day Mate,
At least 2 reasons, 1 as stated above, bushes on the conrod big end & gudgeon pin, & 2, the oil takes a lot of heat out of the engine, lower the oil content, & raise the temperature of the engine.
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