Dealspeed

My Feedback: (17)

I went out to the shed and spun all three over and they feel gummy but that's about it, not at all gritty so I may be ok, I'll give them a good soak and go from there, thanks for the help

1QwkSport2.5r

The gritty reference is in regard to after the soaking/cleaning. If Saito has a regular type 4-bolt backplate, pop it off to soak it. It will work better and faster than just dunking the whole engine completely assembled.

N1EDM

My Feedback: (2)

Hello Fellow Glowheads,

I obtained a OS 28F heli engine as part of an estate sale. It's in really good shape, but I don't fly Heli's. I noticed that there are other versions of the 28 for aircraft. Does anyone have any of these hanging around, old, rusty, and burned out? My reason for asking is that I need the airplane head for this engine, as well as a muffler.

I just wondered if anyone here had a junker airplane engine that they wanted to sell for parts??

Thanks,

Bob

aspeed

You could just get a friend with a lathe to turn the fins mostly off. I just got a .32F at a swap meet on the weekend too. I will have to make a head, or plug and rethread the glow plug thread hole as it is stripped.

Sport_Pilot

Nitro is not acidic. Nitric acid is only in the exhaust as it burns not the crankcase it reacts quickly and would not be in the crankcase. The crankcase may have other acids. I have not observed any adverse corrosion from using high nitro in any engine. However the mags from a nitro modified a friend had, many years ago. would frost the mag wheels over time from the exhaust.

Sport_Pilot

Why the American flag behind a Japanese engine?

1QwkSport2.5r

So no exhaust residue/contaminants gets blown past the piston ring and thus into the crankcase of a 4-stroke engine? Oil certainly does which is far more viscous than exhaust gas is.

Nitromethane isnt supposed to have any acids in it, but I've heard some "cheap" nitro sometimes does. Regardless of that, burning nitromethane does produce nitric acid in minute quantities and one would have to assume that some of those exhaust contaminants will blow past the ring and into the crankcase. An engine run on fuel with no castor oil whatsoever should not gum up and if an engine does, there are other forces at play that would cause such a situation.

aspeed

We used to run 50 to 80% nitro in our motors. If we did not use after run oil, it would rust the piston cyl. in a few hours. That was of course before ABC came along. We normally used synthetic/castor blends, but the nitro was pretty corrosive. I would guess the bearings didn't like the nitro either, but never noticed. That was 40 years ago when I was a kid. Just another comment, I used after run in a motor that I kind of forgot about, and it turned to tar. I couldn't turn it over at all, and it was quite hard to clean. The piston was down, and it turned freely with ball bearings, but the cylinder was black. I think I used transmission oil, or maybe 3 in 1. What's the lesson here? I don't know, but maybe I will turn over my motors every couple of years to check.

Sport_Pilot

Burning 100% nitro does which is why the dragster drivers wear a mask to filter out the large molecules. But when you add more than half the amount of methanol you don't which is why we don't have to worry about the highly toxic gas. Ok, maybe very very small amounts. And the fuel and air in the cylinder burn from top down and you get fuel and oil in the blowby and almost no exhaust gas.

Sport_Pilot

You cannot burn 80% nitro. At least not unless you run 10% oil. I believe you need at least a small amount of methanol to keep the glow plug lit. I have run 60% nitro with no ill effects. But that was with castor oil so maybe synthetic would have been different. I don't think there have been any 4 stroke engines that can run that much nitro without modifications, that is lowering the compression ratio. Their is no exhaust gas or residual blow by in the crank case of a two stroke. In race cars the corrosion I have seen was immediate, not in a few hours. Not doubting their is no issues with 70% nitro and above as I have not used it but I have my doubts.

spaceworm

Ok, then just what is it that rusts the bearings in 2 stroke engines? My balls don't rust as I use some castor in the fuel and also air tool oil for after run.

Sincerely, Richard
Club Saito #635; Saito 56, 100, 120abc, 130T, 180

aspeed

I only used 80% nitro for a record attempt type flight. I would never use it in a 4 stroke. The rules are now 10% fuel in all the speed classes so it doesn't matter. A good rule IMHO, the .049's seem to thrive on the nitro though. Some guys would mix a bit of propylene oxide with the high nitro, but I could never source it. I have had some rusty bearings, but that was more of a storage problem. I think 4 strokes don't get oil on the lower end, so maybe that is why they have a rusty bearing problem. I can't say for sure, I only have one of those. I normally would run a motor dry before storage, so there would likely be no fuel left in the motor.

earlwb

Ok the corrosion is caused by the oxygen and moisture in the air. That oxygen and moisture mixes with residual acids inside the engine leading to corrosion. There is also some electrolysis or galvanic corrosion that occurs between dissimilar metals. The electrolysis also called galvanic corrosion happens when tiny electrical currents that flow between the different metals. Moisture or water helps to facilitate the corrosion. Oxygen of course is a powerful oxidant and the corrosion of ferrous metals is actually the metal oxidizing and turning into rust metal. The residual acids inside the engine tend to aid in corrosion when water and oxygen is present.

Some oils work better at protecting metals than other oils do. Castor oil tends to have a strong affinity for metals and thus forms a strong protective film on the metals. This protects the metal from moisture and oxygen. There are some other oils that work well like this too. But not all oils are so protective. Some oils can still let a model engine rust out, even if you submerged the engine in the stuff.

Model engine bearings tend to be quite susceptible to galvanic corrosion. It leads to tiny pitting occurring on the balls or the races. The oil should help keep the parts apart enough to insulate them from the tiny electric currents that could start flowing.

Usually a model engine that had castor oil in it and was all gunked up badly and stuck, can come out looking good with smooth bearings after a thorough cleaning and re-lubing with fresh oil.

aspeed

I have had most rust on bearing cages, not the balls or races. The K&B bearings had some kind of plastic that always seems to gum up in a few days, but loosens when you use it. I guess the plastic would slow down the galvanic reaction more so than a dissimilar metal cage. And yes some cages look pretty nasty mostly from the castor goo. It is hard to tell if it is rust or goo.

N1EDM

My Feedback: (2)

Hi aspeed,

Turning down the head is an option... I used to have that capability when I was working. Now that I'm retired, I don't have access to my old machine shop any more. Yes, it could be turned down if I can find someone to do it. Finding someone with a junker engine is somewhat easier though, ya gotta admit :-) :-)

Bob

aspeed

Ya, it would be better to get a suitable head. A hacksaw and belt sander may work too. I thought I would use that method, to get the worst of it off, and then put it on the lathe to finish it up. I would do it for you, but our postal service would likely be $20 to get across the border. I think on my .32 F, I will have to make a new head. I may use a turbo plug if I go to all the trouble. To use the old head which is stripped, I would have to insert a plug, drill and tap it, and still get the fins off. Then again, mine has squarish fins, to make it difficult, and I don't have any aluminum stock large enough. I got a .32 SX at the same time which looks much better, but the plating is peeling at the very top. Needs a rear bearing too. Crappy OS. I thought they were supposed to be good.

1QwkSport2.5r

Use a Nelson plug instead. Cheaper and last longer.

N1EDM

My Feedback: (2)

I appreciate the thought, aspeed. In the end, I could butcher the head and then sand & file it to final shape, being aluminum. For now, I'm just going to leave it as is. I think I can get a muffler off an old eBay junker engine (heli, like mine) for cheap $$ to get what I need.

Bob

skyrat71

Bob, If you find a .28F junker to rob a head off of, I'll take the rest of it off your hands. Come to think of it, I probably still have an airplane muffler for one if you want it. I run a very beat-up and worn-out 28F in my 1/6 scale Cub with a home-made muffler swinging an 11X4 prop. Never really revs up and sucks down a lot of fuel(blows it out the sloppy bearing seals) but has never really given me any problems. I built the plane around that engine though and dread the idea of chopping the Cub up to fit a different engine into it if this one ever gives up.

aspeed

I can't find a reasonably priced 11/32 - 32 tap, and I already have a tap for the turbo plugs. I get the plugs for $5 from Merlin. They are the same price as his Nelsons and even the regular ones. I like his Nelson plugs though because they take a regular glow clip, not the Nelson type with the bigger hex.

1QwkSport2.5r

I've never seen a Turbo plug cheaper than $10/ea. if you can get them that cheap then go for it. McMaster-Carr has a 11/32-32 tap for $33. That's is a bit steep.

blw

My Feedback: (3)

The only engine that developed rusted bearings on me was one that used only Cool Power. I bought it from a guy and was using CP too at the time. I switched to Omega shortly after that.

aspeed

Oh, the Merlin price seems to have gone up to$7.95 now. I bought a dozen last year at Toledo. He gave me one extra too. He has the Glow Bee flat coil type as well, I haven't tried them yet. At least with the Turbo type there is a variety of companies to try and the flat on the bottom is about 1mm smaller diameter. It does come at a price.

earlwb

Special taps or dies are expensive, as there is a very limited market for them. So they don't make them much. 1/4x32, 11/32x32 are a couple examples.
Yes the tap is expensive. Unless you have a lathe with thread cutting capability, you will need to buy the tap.
But wait till you want to thread something for a Cox .049 engine cylinder. The 17/32-40 taps or dies are rare nowadays and would have to be custom made for a good price.

N1EDM

My Feedback: (2)

I can help a little bit here. McMaster-Carr has both taps in stock at www.mcmaster.com . Look for part numbers 2521A427 for a 1/4"-32 hand tap (about $7) but the 11/32"-32 is pretty expensive as you point out - about $33 each. Look for p/n 2595A638 for that one.

Just my $.02

Bob
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