Posts: 653
Joined: 6/20/2006 From: Hamilton,
OH, USA Status: online
quote:
ORIGINAL: proptop
Guys...got a question here... Have you ever removed the rear cover of an engine (espacially a 4 stroke ) that has sat for a while without flushing, and smelled sort of a nostril burning acrid (kind of like RTV silicone?) smell? I mean it's the nastiest smell I've ever encountered in dealing with model engines.
What is that? Would that be nitric acid smell that I've heard about, as the combustion by-product of nitro...or maybe formaldahyde(sp?)
I was given a collection of engines and none ever had ARO used... Some were fine inside, and some had rust...but especially the 4 strokes with that horrible smell!
Nitric acid does have an acid smell, so I suppose that could be what you were smelling. The fact that you noticed rusting mostly in the engines with the acidic smell, tends to indicate you could well be on to something.
On the other hand, ANYTHING that is closed up for a while is likely to develop some type of odor. Some of the worst smelling water in the WORLD is held inside sprinkler pipes that hasn't been flow-tested for several years.
Posts: 86
Joined: 5/16/2007 From: Rison,
AR, USA Status: online
quote:
ORIGINAL: Sport_Pilot
quote:
I just changed both rear bearings in my evolution and my super tigre,the bearings were not worn out just rusty
If they were not worn, not loose, and not making noise then there was no need to replace them. The shields on bearings will rust long before the bearings. They are also hot enough to bake the castor oil to a red brown stain which is often mistaken for rust.
the cages and races were rusty,as a 2 cycle motors fuel/air has to pass thru the bearings, and given that rust is abrasive, I thought it prudent to change em out to "keep the pinch" so to speak.
Posts: 7727
Joined: 1/21/2002 From: Acworth,
GA, USA Status: offline
quote:
Have you ever removed the rear cover of an engine (espacially a 4 stroke ) that has sat for a while without flushing, and smelled sort of a nostril burning acrid (kind of like RTV silicone?) smell? I mean it's the nastiest smell I've ever encountered in dealing with model engines.
It's not nitric acid as that is not produced till it burns and thus is not in the intake, that is not in the crankcase. Likely it is the methanol reacting to aluminum, and/or possibly castor oil going rancid. Methanol is corrosive with aluminum even without mixing with water. So run the fuel out at the end of the day.
Posts: 4504
Joined: 10/18/2002 From: Rome,
NY, USA Status: offline
quote:
ORIGINAL: Sport_Pilot
quote:
Have you ever removed the rear cover of an engine (espacially a 4 stroke ) that has sat for a while without flushing, and smelled sort of a nostril burning acrid (kind of like RTV silicone?) smell? I mean it's the nastiest smell I've ever encountered in dealing with model engines.
It's not nitric acid as that is not produced till it burns and thus is not in the intake, that is not in the crankcase. Likely it is the methanol reacting to aluminum, and/or possibly castor oil going rancid. Methanol is corrosive with aluminum even without mixing with water. So run the fuel out at the end of the day.
That's the thing SP...I know the history of most of these engines, and the guy who gave 'em to me...known him for 30+ years...and he always ran the fuel out at the end of the day...that's one reason why I'm wondering about this?
Could be residual methanol? Could also be nitric acid too right? I mean if oil gets past the ring in order to lubricate basically the whole engine, I suppose the nitric acid could too, aye?!
The smell is hard to describe...it's just an eye watering, nostril burning YUK!
Edit: Is Formaldahyde the result of methanol's contact with Alum.? I have seen the whiteish "cheese" that can sometimes result, in the carb of a 1:1 race car that ran on alcohol, but the smell wasn't the same.
< Message edited by proptop -- 11/22/2007 3:09:32 PM >
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Posts: 7727
Joined: 1/21/2002 From: Acworth,
GA, USA Status: offline
quote:
the cages and races were rusty,as a 2 cycle motors fuel/air has to pass thru the bearings, and given that rust is abrasive, I thought it prudent to change em out to "keep the pinch" so to speak.
If brownish red, darker than surface rust, it was likely the castor oil varnish mixed with the red dye in the fuel. If it is rust it will also feel rough, varnish is fairly smooth. If rust it will not generally flake off except on or near the wearing surface. I have only had one bad bearing since the 70s, and though I went 15 years without flying the model and the last 4 or so of occasional flying I have had many motors without rust or bad bearings. IMO the trouble of replacing a bearing with a little rust on the cage is not worth the effort and not the price of most motors. I'd rather wait till the bearing is actually worn. I'm not sure you can even be sure its rust till you remove the bearing. Except maybe on large engines where you can get your finger in to touch it.
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Joined: 1/21/2002 From: Acworth,
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quote:
Could also be nitric acid too right?
I missed the fact that it was four stroke motors. Nitric acid is very reactive so it won't be there by the time you open the crankcase up, but it can react with the oil to form other acids. Nitro is also a mild acid in itself, so I suppose with the right exhaust residue it could react with a base and produce some foul chemical. Never had this problem though and I do not use AFO, but do run them out.
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Joined: 10/18/2002 From: Rome,
NY, USA Status: offline
You can usually get a Q-Tip in there and swirl it around to see if it's rust, or varnish, or a combination of both...
Also..if the balls are not bright and shiney...like if they are a dull gray, that means they're getting worn. You can usually see pitting in them too if you use a magnifying glass or "geezer goggles"
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Posts: 4504
Joined: 10/18/2002 From: Rome,
NY, USA Status: offline
quote:
ORIGINAL: Sport_Pilot
quote:
Could also be nitric acid too right?
I missed the fact that it was four stroke motors. Nitric acid is very reactive so it won't be there by the time you open the crankcase up, but it can react with the oil to form other acids. Nitro is also a mild acid in itself, so I suppose with the right exhaust residue it could react with a base and produce some foul chemical. Never had this problem though and I do not use AFO, but do run them out.
I wonder if some engines could be more prone to this (the smell, and/or reaction ) because of (perhaps ) a slightly different alloy used?
The fuels used were either Powermaster or Omega, which are the exact same as the fuels I use, but I very rarely run any 4 strokes.
There's probably some kind of strange "chemistry" going on in there...
< Message edited by proptop -- 11/22/2007 3:19:03 PM >
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Posts: 86
Joined: 5/16/2007 From: Rison,
AR, USA Status: online
Sport; thanks for these words of wisdom,I will keep them in mind next time,but I think the key for me is to run all the fuel out after flying and maybe after run ATF/air tool oil
on another note the bearings that I changed out in the Saito .50 were very rusty and rough, along with the crankshaft and cam gear,the replacement bearings were sealed/shielded so should last longer without rusting,I just hope they get enough lube. they were saito oem replacements
Posts: 211
Joined: 2/2/2007 From: Golden Valley,
AZ, USA Status: offline
I never used an ARO ever til I started reading what guys say on thease web-sites. None of my old engines that were stored for 15-20 years show any sort of rust but they were lubed with gun-oil before storage. I used nothing but "Dukes" back then. Now I'm using P/mstr. 10% synth/castor blend, and am wondering if a good "gun-oil" like Outters wouldn't hurt for an ARO as it's designed specifically to deter rust in fishing reels and guns. I'm also no chemist, but is Morgans issue with ARO's due to the fact that a "bean-oil" (castor) won't mix with a "mineral-oil" ? (atf/gun-oil) Theres gotta be a reason they printed that on the jug I'd think. Intresting thread!
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Joined: 3/20/2002 From: San Bernardino County,
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I always get a kick when I see a Guy at the field put a few drops of some snake oil into his carb at the end of the day, and give the prop a few flicks. It gives him a warm fuzzy feeling, but does nothing for his main bearings. Then there's the guy that pulls the glow plug and puts some drops directly onto the piston. That accomplishes the same thing for his bearings....nothing. I alwys wonder what happens to the glow plug when that foreign oil soaks it on the next attempt at start-up.
Take a look at these pics of one of my engines I pulled down because of a liner flaking problem. See all that nice clean castor oil in the crankcase ? Look at this backplate....it looks like I dipped it in a cup of clean oil, then let it stand for about 10 minutes, then took the picture. My engine internals are covered with, and protected by the the finest oil provided to us on this Planet.
Why would I want to add some other "oil" to this perfect scenerio ? I wouldn't.
I have automatic transmissions, and I use automatic transmission fluid in them. I have air tools, and I use air tool oil in them. I have aero-model engines and I use castor oil in them.
Synthetic oil "flashes" and burns away completely....that it what it was designed to do. It doesn't leave anything behind. That is why your airplane stays cleaner with the synthetic. The castor does not flash (burn) away....it stays and does what it is designed to do....the best part is that it will seek out and lubricate the hottest parts of the engine, while the wimpy synthetic oil runs and hides.
Could one of you ARO guys and non-castor believers look at these pictures and offer an explanation about why I should try to improve this lubrication scenerio ?
FBD.
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Joined: 6/27/2006 From: Glencoe,
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I've never used after run oil since I think it's just another BS item to buy and it doesn nothing for your motor except burn. Been flying since the 80's and never encountered any rust even during the winter months. No issues ever no lost bearings.
It's not the oil, it's how you tune and run your engine. Like some one posted, to each his own.
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RE: DO NOT USE AFTER RUN OILS! - 
