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Glow motors and oil content - why so much?


Nigel R
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36 minutes ago, Peter Christy said:

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

 

 

Dont get me started on the 'its castor or nothing' crowd. Its always the same argument. 'my mate tried synthetic back in 1973 and it melted his merco. Im never trying that stuff' 

 

Yea its cool, a lot has changed since 1973. It will be fine. 

 

As a side note, given the propensity for modellers to always think they are right, could it also be that manufacturers just couldnt be bothered with the hassle of trying to explain why newer low oil fuel was good for them? A customer of mine recently bought a new engine and upon telling a well known model shop in the uk about the engine and our new fuel they went out of their way to tell him it was going to ruin the engine, they wouldnt recommend oil that low etc etc. Even when he explained that 7% oil fuel was recommended by us for the engine they still shook their heads and claimed it was no good. 

 

So if a shop reckons they know better than the manufacturer of a product and keep dishing out this incorrect advice, what chance does the average sunday flyer have of making sense of it all. 

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As far as most manufacturers recommending (or historically have recommended) 18% castor, I suspect there is simply a very large dose of "the customer is always right" going on.

 

Anyway I am going to try running a lower percentage oil next time I buy some.

Edited by Nigel R
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  • 1 year later...

Looking for advice on fuel for a Saito 82b. I have been running on a commercial 4-stroke mix with 15% nitro and 17% all synthetic oil. I would like to try lower oil but not sure how low I should go.

 

For this engine I have tried various nitro mixes (all with 17% oil). Anything below 10% does not run well. My next batch will probably have 12% nitro. How much oil should I use?

 

.

 

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My saito 45's and 45 specials all run on the laser 5 optifuel mix as do my OS, Enya and ASP's. In fact, i dont run any of my lasers on laser fuel any more as they are all on low oil so laser 5 should probably be renamed 'everyenginethatisnotalaser 5' 

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Castor is a very old debate, here is one from 2007.

 

There's a lot of good information in there. What I found most interesting was that old engines would tolerate castor, but modern engines built with finer tolerances needed synthetic. My understanding from Andy Green's topic is that all engines will run on synthetic and modern engines could have problems with castor. Nice to read a reasoned debate.

 

Steve

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Yes a never ending story, when I started in around 1966 it was caster, arriving in the south of France I joined a club next to Montpellier airport, where

 didn't have to ask the members what they did, they would tell you 🤣, they all ran with 15% micro Motul a thin red synthetic oil and 2% oc caster which worked for me till I went into Helicopters, that was a different bunch of pilots, they all seem to run on a German clear gooey oil  ( can't remember the name sold by Graupner under the name of Aero syntese and aero syntese 2 )) at 15% which also worked fine without castor but too expensive for me, so back to motul and caster, which over a span of 20 years in my model shop I mixed and sold, till I tried Meccamo model fuel ( made in Marseille ) it cost my 2 customers heli engines and a .90 plane one,  ( at my expense )  so back to my mix, nowadays I buy any cheap junk put 2% castor in and i use that.

Edited by Paul De Tourtoulon
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1 hour ago, Paul De Tourtoulon said:

Obviously you mean that protective coat that will save your engine and bearings when stored,,,

 

 

 

No, it wont. It will polymerise and lock all the balls solid. Once they are locked up, the bearing is finished. 

 

The castor argument is very old (and boring) but it just keeps going as, for some reason, there are those who refuse to accept that it is dead and better options are available. 

I also seriously question the thought process of anyone who will actively look for the cheapest and nastiest fuel they can, and then add castor to it before running it through their brand new engine. Why would you do this? Why would you not try and treat your engine to the best fuel and oil so it can have a long and healthy life? Im sorry paul but your fuel strategy just makes no sense at all. 

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Surely castor was used in early racing engines simply because it could maintain lubrication at higher temperatures than the conventional oils available at the time. The downside is the varnish it created as it cooled down after use at high temperatures. Not a problem with a racing engine as it was likely to be stripped down and inspected before any form of storage. Castor oil can be contaminated by acidic combustion products just as easily as any other oil which can cause a 'chemical' corrosion if left in contact with metals for extended periods. The methanol in glow fuel is even worse being hydroscopic adding to a simple 'rust' type corrosion when air is present. 

 

Modern synthetic oils can handle the temperature at least as well as castor with no 'varnishing' problems. This leaves oil contamination as the only issue. Applying fresh oil to to displace any contaminated oil on internal metallic surfaces is still a good practice before long term engine storage.   

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1 hour ago, Simon Chaddock said:

Surely castor was used in early racing engines simply because it could maintain lubrication at higher temperatures than the conventional oils available at the time. The downside is the varnish it created as it cooled down after use at high temperatures. Not a problem with a racing engine as it was likely to be stripped down and inspected before any form of storage. Castor oil can be contaminated by acidic combustion products just as easily as any other oil which can cause a 'chemical' corrosion if left in contact with metals for extended periods. The methanol in glow fuel is even worse being hydroscopic adding to a simple 'rust' type corrosion when air is present. 

 

Modern synthetic oils can handle the temperature at least as well as castor with no 'varnishing' problems. This leaves oil contamination as the only issue. Applying fresh oil to to displace any contaminated oil on internal metallic surfaces is still a good practice before long term engine storage.   

The High performance kart engines still use castor based oils, the ones with  50 hours between rebuilds on run on basically anything, Rotax doo not recommend synthetics in their 2022 2 stoke top end engines, TKM, Dap Parrilla in the vintage classes all recommend Shell M or Castrol M, these are the engine pulling 19000 rpm not the modern long life engines. 

 

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55 minutes ago, Jason Channing said:

The High performance kart engines still use castor based oils, the ones with  50 hours between rebuilds on run on basically anything, Rotax doo not recommend synthetics in their 2022 2 stoke top end engines, TKM, Dap Parrilla in the vintage classes all recommend Shell M or Castrol M, these are the engine pulling 19000 rpm not the modern long life engines. 

 

I used to race Karts in the early 70s, as part of the South Devon Technical College team. Our Karts competed in Class 4 Standard - basically 200cc Villiers, which could be modified anyway you wanted internally, but had to look standard externally. If you could not exceed a ton down the main straight at Dunkeswell, you weren't competitive! We were very competitive!

 

We had three Class 4 Karts. Two ran on Castor, the third (the one I raced) ran on mineral oil - Molybdenum Disulphide based. Ours was the only engine that did not need repeated rebuilds throughout the season. Indeed, when stripped down between seasons it rarely needed attention!

 

Karts were designed for 10 lap sprints. At the end of the season, we had an hour long endurance race for each class. Each of our karts had a team of four drivers assigned to it. For the endurance race, we used to swap drivers at half distance (you really could not stand any more, physically!). But hold on, I hear you say, that only accounts for two drivers! Well the class above us (Class 4 International - originally 200cc anything goes, latterly 250cc anything goes) only had very few entrants, so Class 4 Standards were allowed to make the numbers up - if you survived your own class' endurance race. Our Kart finished in both endurance races (run consecutively!)  every season I was there. It was the only one of our Karts that did. It was also the only one NOT running on castor oil!

 

--

Pete

 

 

 

Edited by Peter Christy
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