freakingfast

My Feedback: (3)

1# What happens at the end of a pylon race? The fuel is pinched off at speed.
2# What product does Dave Shadel still sell? After run oil. (Good stuff by the way)
3# Does a pylon engine see the run time that a average model engine see before it's rebuilt or retired ? I think not.

Not much spent combustion products after a flight in that engine and I betcha he uses a squirt of his oil too.
He's not a good comparison to a weekend flier.

I don't care what brand of nitro containing glow fuel one uses, I couldn't in good conscious, tell a new/ fellow flier not to use after run oil.

jaka

Hi!
Wanna see a rusty rear bearing from a Kyosho .40 GX engine( Same as ASP)?
Fuel: 5% nitro 20% Castor oil!

Compared to a new WIB C4 bearing...

Sport_Pilot

Most of us run the fuel dry, and I bet most use after run oil. Dave has experience with YS and other makes, not just pylon racers. No two strokes get combustion gas in the crankcase, not at all. This was before he sold after run oil. Nitromethane is less corrosive than the methanol and that's a fact that I supported when I posted the corrosion chart.

Sport_Pilot

That looks like oil stains, not rust. There may indeed be some rust. I wouldn't know till I scraped away some of the stains. I have at least one engine that has worse stains than that and its been running fine for a decade or two. It's a Fox .50 and tons of castor stain in the engine.

freakingfast

My Feedback: (3)

I would probably be correct in assuming that methanol, nitro, oil and additives when combined in a catalytic/combustion process with the gases of the atmosphere would create hundreds of new compounds, many caustic and acidic. A fraction of a percent of some acids will eat steel alive in conjunction with the ambient moisture in the air.

The nitro in itself may not be corrosive but what it mutates into with exposure to air or combustion is another story.

The chart you refer to gives a "D" grade to nitric acid and cast iron, the closest ferrous match to a bearing. Keep in mind that chart is manufactures "grade" rating for diaphragm pump housing which factors in acceptable erosion/life, a far cry from what a bearing race can tolerate.

Sure looks like rust on that bearing to me. I've seen varnish/wax too that's not it. "Oil stains" Really?[sm=drowning.gif]

Ken6PPC

[sm=75_75.gif][sm=lol.gif]

Harry Lagman

Sport_Pilot, if you care to do a few simple experiments, you will see that burning Nitro in an engine will greatly increase the chance of corrosion. I run anything from 0% to 30% nitro in my engines, depending on the application. I have run two-stroke engines on the bench both on 15% nitro and 0% back-to-back and have left those engines on the bench for several weeks (no afterrun oil used) and gone back and inspected them for corrosion. Without exception so far, the ones running nitro have shown signs of minor corrosion whereas the 0% engines were free of corrosion. These engines used the same brand and size of bearing.

Blowby is very real in two stroke and four-stroke engines. THere is always some product of combustion going past the piston and into the crankcase; in the case of a two-stroke of course, to be recycled upstairs again. Even ABN or ABC engines have a significant amount of blowby, especially when things start expanding at full power and maximum operating temperature.

Try it out on two similar engines next time you get a chance.

Harry Lagman

Spot on! It's a distinctive smell alright. I was doing a lot of flying at one stage using 20/20 fuel. I had the misfortune of having the cloth (reeking of that familiar "nitro burn" smell) I'd used to wipe up exhaust residue drape itself over the faceplate of my nice shiny Futaba 9CAP transmitter. A week later, I experienced the horror of seeing the permanent tarnishing of that "plastic chrome" finish - the transmitter looks like crap now, thanks to the corrosive products of model engine nitromethane combustion.

Harry Lagman

Couldn't agree more - Good post!

Pilotsmoe

Everything rusts when you live 2 blocks from the ocean, if I didn't put oil(ATF) in my engines after I ran them, the bearings would be covered in rust(stainless or not)[X(]

Sport_Pilot

That smell is there with low nitro fuel, and not there with 100% castor.

In fact methanol has a stronger smell than nitro.

Sport_Pilot

I am currently out of the hobby right now, so it is not convenient for me right now. I hope to get back in, in a few months, so maybe then. For now why don't you try it and show us your results.

Again there is very little burnt fuel in blow by, and any blow by in a two stroke is caught right back up on the next stroke.

I have been in this hobby for decades and have never experienced rusted bearings in my engines, not even those with high nitro.

Sport_Pilot

I did not say there was no rust. Just that from the photo it looked more like oil stains, there are some blotch's on the crank that may be rust, but some crankshafts rust more easily.

Sport_Pilot

Yes I had some bearings and parts that rusted when I lived on the beach, but no problems with engines.

Sport_Pilot

Yes, but nitric acid is probably the least of the worries.

RC-Bearings

My Feedback: (1)

Mike,

They are in the same ROCKWELL hardness RANGE required for bearings but only a point or two lower than bearing steel. The difference in engines is not noticeable.