We see the black castor build up on pistons and cylinder heads pretty quickly here in the states also (racing engines: Nelsons and Jetts). We run primarily 15% nitro Powermaster (Castor/Synthetic mix). I like to clean up the piston top and head with never dull after about 20 2 1/2 minute runs.

The 80/20 mix that Jaka is talking about is used for FAI racing (not real big in the states) but bigger in Europe and Australia. The reason for 20% castor is due to the high expense of Nitro overseas. Those engines are also running closer to 30k and build up castor varnish pretty quickly.

Optical I R scanner, the lazy way, on the head area in general.

OK, but this is still not accurate enough.

Anywhere you point that IR sensor, you will get a considerably different reading.


I would discount these IR devices as inaccurate enough, to allow a disaster to happen to your engine.

Hi!
Dar ...that is what I call carbon build up...!!
The picture you showed is a typical example of carbon build up inside the combustion chamber and I assume it's there on the piston sides as well.
This carbon build up is a problem when when you want the max from your engines, sport engines as well as other engines.
I agree it's not excessive but it's still there. I have seen much worse.
Using all synthetic oil or a mix of castor and synthetic oil prohibits this.

/Jan K

Jan,


Please enlarge that photo and take a close look.

There isn't a 'build up' of anything there; just a very thin layer of shiny, brown varnish, no thicker than the beautiful, blue anodizing on the outside surface of that head. It is uniform and its thickness is less than 0.02 mm.

Caked carbon/soot is thick and dull (no shine, just black), that accumulates over time, in engines that run with medicinal Castor oil, that has not been cleaned (degummed). I have seen it grow to over 1.5 mm over some past engines' piston tops.


I am sure someone else can post a photo of a really caked up piston...


And... I do use a lubricant package that is 45-50% synthetic oil (lately EDL from Model Technics)..

Hi!
Dar...I have enlarged the picture and I agree it's not that much varnish ...but it still is varnish. And varnish is not good!
You don't get varnish if you run all synthetic oils.
But as it is not that much varnish and as it is in a sport engine you can live with it, it will be no problem.

Regards!
Jan K

The expense of nitro has nothing to do with it. FAI 80/20 fuel is specified only for certain international classes where ultimate power is the deciding factor (CL 2.5cc speed, Pylon and I think one class of free flight). It's purpose is to level the playing field so exotic fuels can't be used. AMA rules are only the local American rules whereas FAI are the international rules used by every other country.

Dar,
To call castor oil degummed is simply a marketing trick. Gum is actually not removed, rather the first pressing of the castor bean has no gum. The second pressing or A grade castor has some green organic material in it. I am not sure this is actually gum.

Thats news to me Downunder. I was under the impression for the lack of Nitro in FAI competition was due to cost abroad. I may have been wrong in including Australia with Europe, but I am pretty sure cost is a factor in Europe.

daven
It's only those few FAI events that specify 80/20 fuel. All the rest of them (like F2B CL stunt which is what I fly or RC pattern) can use any fuel they like. As far as I know the USA is the only country that doesn't operate under FAI rules.