Radial Engines; internal maintenance and rust prevention
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  1. #1
    R/C Newbie
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    Jul 2011
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    Radial Engines; internal maintenance and rust prevention

    Hi Guys,
    I just wanted to ask a question regarding after-run maintenance of radial 4-stroke engines. It seems like I get about 4 opinions from every two people I ask so thought I'd post my questions on here to see what ideas come back.
    I have an ASP-400 5 cylinder radial engine. It's the same as a Magnum 400 and I think its a cheaper copy of the OS 5 cylinder radial. Internally, it's quite complex with bearings and timing gear not to mention all the other internal components.
    I've been following a strict after-run regime at the end of each run using after-run oil inside the cylinders and some into the crank case to stop the insides from rusting. I decided to undo the rear of the engine to inspect inside after not running it for about three weeks and found that the crankshaft, con-rod link pins, bearings and other parts covered in surface rust , heavy in some parts. So I ended up stripping the entire engine, washing every last piece of it and reassembling it so it's back to good as new.
    It seems that adding a few drops of after-run oil into each cylinder and even a few into the crank case does little to protect all the internal components of such a large internal cavity.
    How do I prevent rusting from occurring in the future?
    Is one brand of fuel better than another as far as rust prevention is concerned?
    Should I inject kero into the entire crank case to thoroughly wash out all internal components before adding much larger quantities of ARO or ATF?

    Any ideas and advice are greatly welcomed.
    Thanks in advance!

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  3. #2
    R/C God BIG-block's Avatar
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    Feb 2009
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    Not very knowledgeable on radial engines but I think the same theory goes for any engine running glow fuel. I first of all run the engine while I clamp the fuel line and run the engine till it stalls making sure that all of the fuel inside the carb and the crankcase is used up. After that a few drops of ARO in the carb and each cylinder. Crank the engine over a few times to make sure the oil gets spread and coats the internal surfaces. Seal off the carb and the exhaust so that the internals are isolated from the moisture in the air.
    You need two things to make rust. Moisture and steel. If you coat the internal in oil and block off all inlets and exhausts on your engine then there really shouldn't be any way for the rust to start forming. IMO there isn't much more you can do than that. Also how sure are you that it is rust? Can you see any pitting on the surface of the steel components? If you can't then the brown stuff might just be oil residue from the fuel that is stuck on the surface.

  4. #3
    R/C God RogerDaShrubber's Avatar
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    Jun 2011
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    Corrosion needs 3 things, Oxygen, Water and and Electrolyte. It is an electrochemical reaction, electrons move from doner (metal) to receiver (Oxygen) in the presence of water.

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  6. #4

    Join Date
    Oct 2010
    Under your bed
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    squirt some wd4o or rp7 down the carb while cranking it over, it coats everything alot better than through the plug hole

    put ARO in a bone dry engine through the plug hole and then pull the pullstart casing off, its dosnt even hit the crankshaft as its not getting pushed into it!

    and in all my nitro years, i NEVER ONCE used ARO or crap like that, just ran the engine dry and that was that, never EVER had a problem and i never replaced an engine because it wore out.

    i used to snap cranks and casings and heads off but never replaced it coz it was worn

  7. #5
    R/C Newbie
    Join Date
    May 2010
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    Hi All
    Having just pulled down about 40 four stroke engines and replacing bearings etc, you need to look at how a 4 stroke works, no amount of after run into the carby or cylinders is going to get into the crankcase (unlike a 2 stroke) and lubricate the crankshaft, bearings and underside of the pistons whether it's a radial or single cylinder. The nitro that rusts everything is fuel (with oil)that seeps past the piston and spreads a little oil around to lubricate every in there, while it's apart you will see that a few drops in the crankcase breather practically does nothing to remove whats in there. If it has sealed bearings in it and the breather is at the rear, you after run hardly goes anywhere. So while it's apart have a look at where after run goes when you put it in the breather (normally to the bottom of the crankcase), I think you will have to put about 50 - 100cc in and rotate the engine (and plane) around to get the oil to smother everything inside, you could also stand the plane with the breather pointing up and give the engine a quick blast with a starter to turn it over about 10 times to spread the oil, and then either leave the oil in or take it out and block the breather to stop a mess when transporting it. Having to do all this is fiddly and messy but it's probably the only way to stop it happening again.

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