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Old Apr 04, 2011, 07:50 AM
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Running a OS 40LA RC diesel engine conversion

I used a Davis Diesel Development head to convert a OS 40LA engine into a diesel engine (compression ignition engine). I think the OS 40LA engine works better as a diesel engine than it does as a glow engine.
In this case I used a 12x6 prop on the engine as it likes bigger props as a diesel. earlier I had run the engine with a 10x6 prop, and although it ran with the prop, it didn't want to idle well. As to run with the small prop I had to turn in the compression screw more. But with the bigger 12x6 prop, I can back off the compression screw more to let the engine lug down more. The engine was turning the 12x6 Master Airscrew prop at around 8,600 RPMs.

One other thought is one can use muffler pressure on a diesel engine. it helps with fuel draw at idle having a little pressure to help feed the fuel to the engine.



OS 40LA RC diesel conversion where it idles now (1 min 55 sec)




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Old Apr 04, 2011, 08:17 AM
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Earl, thanks for that, I have an LA .10, LA ..46 and a LA .65 converted to Diesel, they make great Diesels. The .65 though is an excellent glow engine besting some very good glow engines in a 60 sized engine shoot out a few years ago. The Fox .60 won that comparo handily and I think the LA .65 was second.
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Old Apr 04, 2011, 11:51 AM
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Thanks. I still have a Davis Diesel head for a Fox .15 and a Fox .45 too. I plan on firing them up and see how they run too.

I think the Os LA engines made good diesels as they were cost reduced versions of the FP series but they simplified the porting more and eliminated one of the intake ports. That helped the flow characteristics to be more like the diesel engines then. Many of the model diesel engines used two or more intake ports and they didn't have a baffle plate on the piston either. some of the model diesels looked like they had Schnuerle porting for all practical purposes.
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Old Apr 05, 2011, 09:38 PM
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Where is the glow plug?
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Old Apr 05, 2011, 09:44 PM
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Originally Posted by Rusty-Gunn View Post
Where is the glow plug?
There is no glow plug. it is a compression ignition engine, it doesn't need a glow plug.
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Old Apr 06, 2011, 01:07 AM
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I read some where that these motors don't use auto diesel, but a different fuel with the same name. Where do you get this type of fuel?
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Old Apr 06, 2011, 05:40 AM
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http://www3.towerhobbies.com/cgi-bin...&I=LXANCP&P=SM

A quart might not seem like much but will last twice as long as a quart of glow fuel.
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Old Apr 06, 2011, 06:52 AM
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Originally Posted by Rusty-Gunn View Post
I read some where that these motors don't use auto diesel, but a different fuel with the same name. Where do you get this type of fuel?
Yes that is correct. The word "Diesel" as used with the model diesel engines is something of a misnomer. They are actually compression ignition engines that do not use a sparkplug or glow plug to initiate combustion. They do not use vehicle pump diesel fuel. But they do use a special model diesel fuel.
As mentioned already Tower Hobbies sells the Quart cans of Davis Diesel Development fuel. A model diesel generally uses 50% to 60% less fuel than a glow engine does. So a quart lasts quite a while depending on the engine size. Davis Diesel development makes diesel conversion heads for many engines.

You can make your own fuel too. The classic formula is 33% ether, 33% kerosene and 33% castor oil. Some people added a little extra something extra as a ignition improver like maybe 1% or amyl nitrate or something like that.
Variations of the basic formula work well too. Such as 40% ether, 40% kerosene and 20% oil (for ball bearing engines). Really small engines may run 60% to 70% ether, 5% to 20% kerosene and 20% to 25% oil. Some engines like the Drone engines just after WWII actually used 75% ether and 25% mineral oil without any kerosene. Another formula is 60% ether, 20% kerosene and 20% oil for small engines. One can substitute Naptha for kerosene too (Coleman camp fuel for example).

Here in the USA buying ether can be a problem as it is very restricted now, due to the illegal drug labs. But you can get ether in the starter fluid cans for starting automobile or truck engines. John Deere starter fluid cans has the most ether in it with no n-heptane. But other sources such as from Wal Mart work well too. You want the starter fluid that says it has diethyl ether in it without any n-heptane in it. n-Heptane is a relative of ether but it has a slightly higher self ignition temperature and some engines don't like it much. Generally the unscented plain uncolored oil lamp fuel is kerosene.

Now some guys have experimented with zero ether model diesel fuels in the larger size model engines (not the 1/2a 1/8a size engines). In this case pre-heating up the engine and or pre-heating up the kerosene/oil mix before you use it works well. Pre-heating aids the engine in getting the fuel to self ignite under compression by making it easier to reach the self ignition point of the fuel under compression. Previously some guys would start the engine with a ether based fuel and switch over after the engine warmed up good.
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Old Apr 06, 2011, 10:56 AM
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Thank you.
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Old Apr 06, 2011, 11:10 AM
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Our local NAPA store has starter fluid that has "heptane" without the "n-" in front of it.
This can says not for glow plug use.

I've never heard of castor oil until recently, when reading these threads, and have never seen it in our local stores. We do have colman fuel and kerosene though.
What do you guys do to take the starter fluid out of a spray can? Spray it out? Punch a tiny hole in it and pour it out after the pressure drops?
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Old Apr 06, 2011, 12:05 PM
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Here is how to mix model diesel fuel at home:

http://www.rcgroups.com/forums/showthread.php?t=1295580
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Old Apr 06, 2011, 01:48 PM
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They tend to leave the n- off of Heptane a lot.
Heptane is sort of a ether substitute but it has a higher self ignition point than ether does.

Glue Gun's method is good. what I started doing was taking the starter fluid cans and put them in the freezer for a while, to chill them down real good. Then I take the can and over a jar carefully poke a tiny whole in it to let the gas pressure off. Then I can enlarge the hole and pour it into the jar. You poke the tiny hole in the can so that it is above the liquid level. So you can do it from the top or flip the can upside down and do it on the bottom or at the edge too.

what they mean by not for glow plug use is in those automobile or truck diesels that have a special glow plug unit in each cylinder to help in starting the real diesel engine in cold weather.

Oh yeah for model diesel engines you can substitute 20 weight 50 mineral oil for automobiles in the fuel formula too.The early model diesel engine fuel formulas didn't use castor oil in them. The old Drone engines used 75% ether and 25% mineral oil.
You can also use medicinal castor oil from the pharmacy, but it has to be the plain castor oil with no coloring, flavor additives, or sugar added. The plain unadulterated castor oil is the same oil used and sold by the fuel companies.
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Old Apr 06, 2011, 01:58 PM
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Earl,

Was the OS running on your homemade fuel in the video?

Oh and another good thing to add to homebrew fuel is cetane booster. I think my bottle claims that it raises the cetane number of diesel (in this case kerosene) up 5 or something. The higher the cetane, the easier the fuel is to ignite with compression heat alone.
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Old Apr 06, 2011, 02:05 PM
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I was using Davis Diesel Fuel with a little extra castor oil added to it.
I like to use the good stuff as a known good starting point at first, before I try the homemade stuff. so that if I have a problem and the engine won't start or something, it narrows down the troubleshooting issues.
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Old Apr 06, 2011, 03:44 PM
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How does one determine the percent of ether in a NAPA brand Starter Fluid can?

Can any engine be made to use diesel? which brand/size is best?
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