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Speed,Combat,Scale,Racing => Combat => Topic started by: phil c on June 20, 2018, 04:59:15 PM
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Anybody seen this kind of pattern of black on the inside of a head? This is an LA 25 that's seen some pretty hard combat use. Second one I got, I think. It's been run on 23% synthetic or 20% synthetic, 3% castor, 10-15% nitro.
The patch on the squish band leads from the plug to over the exhaust port.
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Forget a picture? Did you mean this one?
(https://stunthanger.com/smf/index.php?action=dlattach;topic=50585.0;attach=286865;image)
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Anybody seen this kind of pattern of black on the inside of a head? This is an LA 25 that's seen some pretty hard combat use. Second one I got, I think. It's been run on 23% synthetic or 20% synthetic, 3% castor, 10-15% nitro.
The patch on the squish band leads from the plug to over the exhaust port.
Phil, what it looks like to me .....
Looking at the area in the bowl around the plug, I see a heavy baked-on carbon build-up. This then carries on towards the exhaust port. These are the areas where the temperature is lowest(Highest? Not sure.) and the carbon gets deposited there and is the cause of the pattern you see, The other areas are hotter(lower?) and the carbon isn't deposited there.
Even though you use primarily synthetic oil, the small amount of castor oil over extended time and running is the cause.
Bill
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Thanks Bill, kinda double posted there.
The carbon comes from castor and burns on where ever it gets too hot. I've got other LA's and FP's that carboned up the whole head. I think the head pictured was on an engine with a Gardner sleeve, but I'll double check. The Gardner sleeves really run well.
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Phil, maybe there were some rough patches where it should have been more polished. The synthetic might have been able to hang around long enough to cook. Though ylall seem to think it was the castor... I'm just guessing about that. Did you mean it's the second L.A. 25 you've got that did this same thing?Could the two engines have possibly been manufactured in the same lot?
Rusty
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Most engines that get carboned up get it from castor oil. Five or six runs on the old 20% castor will gum up an engine in a hurry. Quite a few guys were taking the plane back to the pits and either cleaning the head or running a load of all synthetic fuel to keep the carbon from building up too much. Thankfully the FAI has gone to a mainly synthetic blend now.
I generally don't keep track of each run and each fuel type. This head was surely run on at least half and half castor for a couple of years before switching to all synthetic.
Maybe it just hasn't been run enough to wash out the carbon.
I suspect also that the port pattern in the LA 25 isn't the best. Perhaps someone else can weigh in on whether the FP 25 gets less/more uniform carbon buildup when it does occur.
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Thankfully the FAI has gone to a mainly synthetic blend now.
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Unfortunately not true Phil:
Para 4.4.5.j of 2018 F2D rules:
Standard fuel shall be supplied by the organisers to the following formula: 10% nitromethane 20% castor oil
lubricant (first pressing) 70% methanol. Fuel shall be mixed by volume.
Most large competitions in the US have gone to 5 Castor/15 Synthetic or 20% all synthetic which helps a lot. Not sure what fuel was used at the "bean Field" as I didn't go this year but suspect it was Castor. Local contests we run our own on the honor system and most guys run 5% or less castor and the rest Syn
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Thankfully the FAI has gone to a mainly synthetic blend now.
Unfortunately not true Phil:
Para 4.4.5.j of 2018 F2D rules:
Standard fuel shall be supplied by the organisers to the following formula: 10% nitromethane 20% castor oil
lubricant (first pressing) 70% methanol. Fuel shall be mixed by volume.
Most large competitions in the US have gone to 5 Castor/15 Synthetic or 20% all synthetic which helps a lot. Not sure what fuel was used at the "bean Field" as I didn't go this year but suspect it was Castor. Local contests we run our own on the honor system and most guys run 5% or less castor and the rest Syn
Perhaps it's still in the works. The NATS ED was told it had passed and Rich's Brew supplied the 22/10/68 fuel used for F2D at the NATS.