RTD

Hi Folks,
hope that you can help me understand what's happening to the bearings in my OS91FX. The story goes ...

1. bought new NTN bearings (exact dimensions of the originals), removed the seals except for front seal on front bearing, and cleaned all the lubricant out with petrol.

2. put bearings in the freezer, applied a little heat on the crankcase and dropped them in without need for any force to make them seat properly.

3. lube them up with a little castor oil - smooth a silk.

4. run the motor (fly the plane) on 15% LV Synth (heliglow) + 6%castor + 5% nitro and the bearings feel silky.

So far so good ... all seems well until ...

I store the plane for a month (I'm not in a humid climate) and now the bearings feel notchy, in fact the motor is slightly locked and needs a little force to turn the crank whenever it sits for extended periods. The notchiness reduces when I flush the engine with fuel but it doesn't feel silky like before. There's a definite rumbling feel to them which you can detect through the crank shaft and hear if your ear is close to the motor. The engine still runs really well but I'm not happy with my new bearings. This problem does not opresent it self with other engines using the same fuel with the same brand and type of bearings (eg. OS46FX and OS40FSR). I don't use after run lube (ATF) unless I plan on parking the engine for several months.

What have I done wrong? Are the special bearings that I should have bought? Should after run be used ALL the time?

Your advice will be appreciated.

w8ye

My Feedback: (16)

They have just corroded. It's time for another new set. Might use some oil after every day's flying?

TimC

RTD, I've learned the hard way to pull the fuel line and run the engine dry while still hot at the end of each flying session. Also I use after-run oil after running it dry. (I live in a dry climate and have had fairly new bearings corrode also).

Flyboy Dave

My Feedback: (21)

Step #2 is where the problem started. When you pulled the bearings out of the
freezer and installed them, you didn't see it....but the bearings produced some
condensation on themselves as they warmed up. This rusted the bearings while
they were still new. When you thoroughly cleaned the bearings, you removed
all the rust prevention. (the grease)

The trick is....don't wash the bearings, just blow off the excessive grease with
compressed air. The remaining grease will protect the bearings from corrosion,
but will wash away in an instant once you start the engine.

I'm sorry you had to learn this lesson the hard way. []

FBD.

canadagoose

My Feedback: (2)

It's hard to believe that your bearings have corroded after only a month, but your description makes it sound like they have or the oil in your fuel is turning hard in a very short time, particles in the balls and race can make them feel that way, your engine shouldn't be getting hard to turn over otherwise. I am not sure of the qaulity of NTN bearings, might want to try another set from a different manufacturer like NSK or Koyo if the bearings have actually corroded. I would put them in a hot antifreeze bath for a couple hours and then use some brake and electrical cleaner to flush them out then oiling them up good and then see what they are like before tossing them in the trash can.

Sport_Pilot

Why remove the seals? Wouldn't they have lasted longer sealed with the lubricant they came with? Or were the seals not rated for our speeds?

w8ye

My Feedback: (16)

NTN is a popular Japanese bearing maker. They have been around a few years. They've worked fine for me. I have three engines with NTN bearing in them.

canadagoose

My Feedback: (2)

I remember my ASP 91 2 stroke had bearings that didn't feel smooth either after sitting for quite a long time ( a couple years ), i kept running it anyways. After quite alot of flights they do feel silky smooth now like they were when new.

britbrat

Leaving the seals in place is a certain way to kill the bearings fairly quickly. The glo fuel will wash the grease out of the bearings, but the seals will prevent the fuel/lube mix from flooding the bearing & supplying adequate cooling & lubrication. There would be a good chance of the bearing actually seizing.

Fuelman

My Feedback: (6)

Next time, before you freeze your bearings, oil them up nice with either castor oil or some air tool oil (assuming you cleaned the manufacturers grease out of them, which does not need to occur), then put them in a plastic bag before freezing them.

The other possibility (much less likely) is that you have injested some dust and it has gotten in the bering ball races.

BarracudaHockey

My Feedback: (11)

I would bake the crank case for a few minutes so its heated evenly as opposed to a heat gun. I never found a need to freeze the bearings doing that.

Also consider a set of hybrid ceramics from http://www.rc-bearings.com a set for my 50 helicopter engines is less than 30 dollars.

Sport_Pilot

The seals would have to go bad on both sides for the fuel to wash out the grease. If not sealed on both sides what is the point of the grease. Doesn't OS used sealed pre lubed bearings on some of their engines?

canadagoose

My Feedback: (2)

OS does use some sealed greased bearings. My FS91 Surpass II uses one at least on the main rear bearing not sure about the front bearing. A 2 stroke it seems would be a better engine to use them on because oil doesn't need to get through the main bearing to oil a cam and it's followers and bearings. Both the main and front one would have to be sealed with grease.

britbrat

Bearing seals are not hermetic seals -- they will leak low density & low viscosity fluids (like methanol), while high viscosity fluids (grease) are retained for a considerable time -- unless they are flushed out with a solvent.

The examples given are four-strokes. A two-stroke is the worst possible choice for a sealed bearing -- they have high volumes of solvent in the crank-case, swishing around at high velocities & with substantially variable pressures -- just perfect for pumping solvent back & forth past seals.

canadagoose

My Feedback: (2)

I didn't think methanol could act as a solvent for a petroleum based grease.

canadagoose

My Feedback: (2)

I just tried it, methanol does not mix at all with a petroeum based grease. I put some in a cup and dumped some fuel in with it and tried mixing them, the grease acts like the methanol isn't even there.

Sport_Pilot

Bearing seals are hermetic. In fact many are designed with a grease that will melt into a liquid at opereting temperatures. If the right materials are used they should work in two stroke model airplane engine.

Jackster00

I KNOW that Saito uses sealed bearings (front and rear) on their .30 engines. I have two I replaced out of my .30 and they had seals on both sides. Granted, it's a 4 stroke engine, but why should a 2 stroke be any different? The grease would liquify at running speeds, and I would think that is a better lubricant than castor or synthetic oil in a bath of moisture retaining methanol, otherwise, why would this manufacturer leave the seals in?
Also, if the engine is worth anything, it's worth putting after-run oil in it before putting it away for the day. It's just a little more work, but it's really worth it.

Jackster

canadagoose

My Feedback: (2)

I would say that the only reason that 4 strokes are being fitted with sealed greased bearings instead of 2 strokes is that the 4 cycles get corrosive gasses contaminating the oil in the crankcase where 2 cycles are constantly being flushed with fresh fuel and oil, not because sealed greased bearings wouldn't work, bearing problems are just more prevalent in 4 cycle engines. Does anyone know of a 2 cycle glow engine fitted with sealed bearings?

Sport_Pilot

The four strokes main problem with bearings are the worn bits of metal from the rings and sleeve getting into the bearings causing scratches, ball slippage, and spauling.

Lots of problems with rusty bearings in 2 strokes also. IMO some manufactures should try sealed bearings in there two strokes. OS seems to have this problem.

britbrat

Heat it up until the grease is liquid, then squirt the nitrated methanol at it under pressure -- better yet, put some sealed bearings in one of your 2-strokes & tell us about it.

britbrat

Bearing seals are not hermetic -- they are close-fitting & are designed to retain high-viscosity fluids, not low viscosity fluids -- unless they have lip-seals --- & those won't stand 16,000 rpm.

Put some methanol in a sealed bearing & close it up -- the methanol will quickly leak out -- just like it leaks in.

britbrat

The 4-stroke crankcase is not flooded with fuel, so it needs a sealed bearing -- If it was they flooded, they would use open bearings -- just like they do in 2-strokes.

canadagoose

My Feedback: (2)

Niether is a 2 stroke flooded with fuel, have a hard time running if it was.

Flypaper 2

There are sealed brgs. and shielded brgs. OS engines, 2 stroke and four stroke use shielded brgs, no seals. Also OEM brgs. in OS engines is NTN.