Glow motors and oil content - why so much?

[Nigel R]

Car and buggy engines seem to be thrashed at high rpm on fuel that contains around 10% oil.

Jon of Laser is now happy with Lasers to be run on the low oil mix (8% ??).

Petrol motors seem to use, what, 15:1 mixes?

Will it really end the world if I run a 10% blend in a decent modern two or four stroke?

 

[James Green2]

I'd be very interested to know people's thoughts on this, good post. ?

[Jon H]

Yep, too much gloop in glow fuel. 

Modern (last 30 years at least) 4 strokes with bronze bushed big ends will most likely be ok down to 2 or 3%. Most petrol converted glow engines use 20:1 (5%) but use less fuel. In terms of oil volume, that probably works out to somewhere in the 3% range in glow terms. Using your 15:1 example, you are still in low single digits. The laser 180 petrol uses 50:1, so about 1% in glow terms, and i have run a 180 glow on 40:1 methanol oil without ill effect. 

2 stroke are slightly different as the fuel dilutes the lubricant making is less effective. Methanol is worse than petrol as a lubricant, but both are functionally the same..ie, useless. I would tend to go for more oil on a 2 stroke than 4 for this reason. Still, as you say, 10% is a great deal cleaner than 18 or 20. 

At the end of the day, a lack of oil will always give the same failure. Big end bearing seizure to the crank pin. If its not seized up, its fine. 

The only thing to watch is running the engine super rich. If you run slobbering rich you will wash all the oil out of the case and that wont do it any favours. But, running rich is bad for the engine anyway so its just another reason not to! 

In summary, i would expect all 2 and 4 stroke engines with bushed rods to run just fine on 5% nitro 10% synthetic oil fuel provided they are tuned correctly (not rich!!) and are cooled in a reasonable way. Engines without bronze bushed rods (Saito) should probably stick to 15% just to play it safe. 

I am happy for customers to run Lasers on the low oil fuel from model technics. Over time i will work to reduce the oil further. Although i am confident 5% would be fine, it would be a little irresponsible to just run with that straight out of the gate just in case. We know 10% is fine due to our own extended testing and i ran 5% on two of my engines for a year without incident, so dropping to 7.5% is a reasonable start for us. 

Edited February 12, 2021 by Jon - Laser Engines

[Nigel R]

Thanks Jon, I had hoped you would add your expert opinion.

I note Model Technics have sold Super Tigre fuel for absolutely ages with only 10% oil content.

One thing

Quote

 If you run slobbering rich you will wash all the oil out of the case and that wont do it any favours

Surely... (potential silly question) very rich mixture would simply mean a higher volume of both oil and methanol sloshing through the crankcase?

 

[J D 8]

                      If you run a two stroke slobbering rich it will run like a four stroke or even like a vintage "hit and miss " standing engine which fire once only once every 6 to 8 strokes.  This would result in a lot of unburnt methanol washing the oil out I recon.

[Jon H]

My comment about oil washing was mostly related to 4 strokes as they only have oil...'down there' so any methanol will dilute it.

However In a 2 stroke the fuel in the crankcase is a vapour and the oil then separates out to do its work. If you have so much methanol that it is sloshing about then you end up with a similar situation. This video (start at 3 mins) shows what i mean. You can clearly see the oil has separated from the fuel and you dont have methanol floating about in there as its all in gaseous form

 

[Martin Harris - Moderator]

Any plans to follow this lead Jon?

?

[Jon H]

not unless the durability improves!

[J D 8]

  Interesting how the oil pools some in the bottom of the crankcase. What happens if the engine is inverted ? Pool in the piston ? probably not given it is being chucked about so much. Would think that piston would get better lubrication and cooling though.

   I have an old Gunson colour tune, a device to help in the set up of old petrol engines.  It allows one to look into the combustion chamber while the engine is running and adjust/tune the mixture. Just fascinating looking at the combustion as it happens.

  A " hero "of mine is Harry Ricardo who was responsible for much of the innovations/developments of the internal combustion engine in the last century many of which are still used in engines today.  In the 1900's he developed and sold a two cylinder two stoke piston engine that instead of using atmospheric pressure to induce the charge it used the pressure developed by the down going piston.  He had little luck selling it to car makers but fishermen used it in their boats, they liked that it ran smoothly and would tick over nicely.

 

 

[Frank Skilbeck]

It looks like the centrifugal forces spin the oil to the wall where the bottom end picks it up , after a certain level has built up it then gets "sucked" up the transfer ports, so the level is not determined by the orientation of the engine. But it would be nice to see the engine running inverted and also a typical four-stroke as well. I suspect on a four-stroke there would be much more oil in the crankcase as there is no real through flow.

This would suggest that the amount of oil in the crankcase isn't determined by the oil content, but the oil content would really determine not how much oil is in the crankcase but how often it is "changed" or renewed, so a 20% oil content would be changed 4 times as often as a 5% oil content, so more beneficial where the oil degrades quickly, so a lower oil content with a higher quality oil wouldn't be an issue. 

BTW my Laser 150, 200v and ASP90 are all running on 10% synthetic oil and there seems to be plenty of oil in the engine.

[Jon H]

I did an experiment a few years ago where i took one of our v twin crankcases and built, essentially, a 180 single with a big hole in the crankcase. It was very interesting watching the crank and rod whizz about and i was surprised how little oil flew out of the hole. Anyway the movement of the conrod past the crank gave a lovely strobe effect and we could see rings of oil moving outward as the engine ran. If anyone has a high speed camera i will knock up another and we can film it

Frank, you are quite right. as with most things quality wins over quantity. 

One thing that did occur to me is that plain bearing engines (os FP and LA series for example) may need more oil to help seal the main bearing. As with all plain bearings there is a small clearance there and a nice goopy oil will seal it. I have an old 249 PAW diesel with a worn pain bearing and it blows fuel/oil from the front of the crank and makes a dreadful mess. I might mod it to take some ball races..hmmm

[Martin Arnold 1]

Hi guys.

Just thought I would add my two penneth, have been running all my Saito and OS 4 strokes on 10% oil for the last 15 years or more with no ill effects and I do like to let them rev !! Have been using Model Technics Dynaglo 5, oil is 8% EDL 2% castor, there are other advantages too, more methanol which is after all the fuel and a lot less slime on the model to wipe down.  

[Jon H]

22 minutes ago, Martin Arnold 1 said:

Hi guys.

Just thought I would add my two penneth, have been running all my Saito and OS 4 strokes on 10% oil for the last 15 years or more with no ill effects and I do like to let them rev !! Have been using Model Technics Dynaglo 5, oil is 8% EDL 2% castor, there are other advantages too, more methanol which is after all the fuel and a lot less slime on the model to wipe down.  

The amount of methanol per cc/ml etc of fuel will be greater, but the amount of methanol used by the engine will be the same irrespective of oil content as the ratio of fuel (methanol) to air remains constant. But, a lower oil content and its greater % of methanol per unit of measure means you can run a leaner mix and this improves overall fuel consumption. 

As an example, on 7% oil Lasers only need about 1/3 to 1/2 turn of main needle to be tuned correctly. 

[Nightflyer]

Having raced ic powered cars at National, European and World level now some years back, and still race occassionally people were often looking at fuel mixtures and Jon's comments are right. Manufacturing processes and materials means that bearings and parts in general are to a higher tolerance and quality meaning that oil levels don't  need to be as high as they used to be and some of the fuels used by racers tend to be lower oil content 10-12% synthetic oils, but equally the fuels tend to use higher nitro content levels to that used for general purpose model flying. 

At the same time though there are a lot of model engines out in the world of varying ages so keeping to traditional ratios means they are not affected.  0ver the years I have used various fuels for my flying car racing and model power boating but there are some that are good for all three while some that are good for car racing that are definitely not so good for say power boating. 

[Nigel R]

On 13/02/2021 at 00:33, Jon - Laser Engines said:

However In a 2 stroke the fuel in the crankcase is a vapour and the oil then separates out to do its work. If you have so much methanol that it is sloshing about then you end up with a similar situation.

Ah - I get it now.

With far too much methanol I guess it would not vapourise quick enough?

I can understand the differing needs of plain bearing motors.

17 hours ago, Jon - Laser Engines said:

I did an experiment a few years ago where i took one of our v twin crankcases and built, essentially, a 180 single with a big hole in the crankcase. It was very interesting watching the crank and rod whizz about and i was surprised how little oil flew out of the hole.

I changed bearings on two OS 40s recently. Bench ran them to check all was well immediately after doing so. On one I had failed to tighten the backplate screws (oops) and the amount of oil that was blown past the 'seal' between backplate and crankcase was very high. I guess particular places in the crankcase have the oil pool as per the two stroke video above... by contrast the more normal vent locations clearly do not have any oil pooling there.

[Jon H]

In the case of your leaky backplate you were not just blowing oil out, but the fuel charge itself from the crankcase. In the test i did the only oil in the crankcase was the oil left over after combustion and ejection of the gasses from the exhaust port. Whatever was then stuck to the cylinder wall etc was then scavenged into the case by the rings. Some oil will no doubt go out the window with the exhaust gasses, no idea how much mind you. I could probably test it but tis hardly a vital piece of information

 

Edited February 15, 2021 by Jon - Laser Engines

[Nigel R]

hopefully not fuel charge! they were four strokes.

 

[Jon H]

34 minutes ago, Nigel R said:

hopefully not fuel charge! they were four strokes.

 

ah, i thought 2 stroke 

[Nigel R]

Coincidentally, I have also just run a pair of 46 two strokes which I changed bearings on.

So much oil and mess!

 

[Martin Harris - Moderator]

Lovely!

[Nigel R]

Ha! Not what I was saying at the time...

The most sensitive needle I have ever come across. Runs great at exactly one position.

You can imagine the rest.

[Maurice Dyer]

Hi have been running four strokes on 15% synthetic 5% nitro for years. 

Cheers

[Peter Christy]

A lot of the problem was down to manufacturers insisting on 18% oil minimum, or they would void the warranty!

I was once party to some experiments with glow fuel at 15% oil. Never had any issues with it, and it ran clean. However, for sale to the public, they had to increase the oil content to 18%, as the agents for one of the major manufacturers openly stated that they would refuse warranty claims if the fuel contained less than 18%! As a result, no-one would buy it unless it was 18%!

The only significant difference was that 18% ran noticeably messier!

(This was around 20 years ago)

--

Pete

 

[Jon H]

As we have touched on before Peter, the problem is 5% of a decent oil will lubricate much better than 20% beef dripping. Going back a way castor oil varies in its quality quite substantially and i suspect most mfr's were just covering their backsides. 

 

Also, for years noone complained about the oil, so they just left it as they had always done it that way. Petrol rocked that little boat and now here we are. 

[Peter Christy]

I'm not disagreeing, Jon! I would have happily run my motors on that 15% stuff (it was a very good synthetic - still use it today!). My point is that had the people concerned been more specific - say 18% for castor, less for high quality synthetic - we would have been reducing the oil content for decades now.

 

And you would be surprised (or maybe not!) how many folks out there still stubbornly continue to believe that castor oil is essential for a model engine!

 

Sometimes I despair!

 

--

Pete

 

Edited February 18, 2021 by Peter Christy