about bearings
 

can someone tell me if a sealed bearing filled with grease and installed in a engine can produce much more friction compared to the older bearing that had only one shield and no grease?

RE: about bearings
 

The grease seals will impart a small amount of drag. The short answer is Yes.

RE: about bearings
 

If you're talking about the smaller front-bearing then I can say from practical experimentation that the difference is so small as to be immeasurable.

While some say you ought to pull the inside seal and flush out the grease inside, the reality is that it makes no practical difference.

The front bearing will long out-last the rear bearing in model engines and the drag of the single extra seal is so slight as to have no effect at all.

In theory, the grease may provide extra drag but even though the bearings are sealed, it appears that oil from the motor eventually flushes the grease out anyway. (yes, even in sealed as opposed to shielded bearings)

RE: about bearings
 

This is from Paul McIntosh of [link=http://rc-bearings.com/]RC-Bearings[/link].

The double-sealed, grease-packed front bearing must be left as it came. It will never need any added lubrication and will outlast the engine itself.

This is true of all bearing types; steel and ceramic balls.


Removing the bearing's inner seal and flushing the grease out will just 'expose the bearing to the elements'... This means FOD, corrosive materials and lubricants inferior to the grease it was packed with...

More drag, sure! But the magnitude is nearly immeasurable.

RE: about bearings
 

For sure you wouldn't want any of that nasty oil we use getting into a bearing. Ummmm, can't think of any other nasty "elements" it might be exposed to... :D

Actually I have to fit a sealed bearing to a Moki M5 I've got because it sprays fuel out the front like nobody's business but I'll be removing the rear seal and getting rid of the grease. And yes Dar, I know where the sealing area is but seeing they only made about 1400 of these engines a long time ago I have my doubts the LHS will have a spare crankcase in stock :).

RE: about bearings
 

As soon as you crank up the engine the excess grease starts leaving the bearing. Within short order the extra drag of the excess grease is gone.

All it takes is a few seconds at full throttle.

RE: about bearings
 

Quote:

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ORIGINAL: downunder

Quote:

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ORIGINAL: DarZeelon
Removing the bearing's inner seal and flushing the grease out will just 'expose the bearing to the elements'

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For sure you wouldn't want any of that nasty oil we use getting into a bearing. Ummmm, can't think of any other nasty "elements" it might be exposed to... :D

Actually I have to fit a sealed bearing to a Moki M5 I've got because it sprays fuel out the front like nobody's business but I'll be removing the rear seal and getting rid of the grease. And yes Dar, I know where the sealing area is but seeing they only made about 1400 of these engines a long time ago I have my doubts the LHS will have a spare crankcase in stock :).

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Brian,


If you compare the lubricity qualities of the bearing-grease the bearing is packed with, to castor/synthetic oil, diluted with methanol+nitro and 'laced' with nitric and other acids...

...Then, yes! That would expose the bearing to some nasty elements...

I suggest you do keep both seals in the bearing, as well as the grease packing.


And as to the crankcase; I do understand you will only be dealing with it 'symptomatically'... But it is definitely better than living with all that goo all over the plane.

Keeping the bearing as it came; seals, grease and all, will make the seal (of the bearing between the crankcase and the crankshaft) a little better...

RE: about bearings
 

smaller sized sealed bearings dont create too much friction because the seals are smaller.

but ie with a 160FX rear bearing, with seals and without seals are like night and day. The sealed bearing on that size feels incredibly heavy to turn.

RE: about bearings
 

Quote:

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ORIGINAL: w8ye

As soon as you crank up the engine the excess grease starts leaving the bearing. Within short order the extra drag of the excess grease is gone.

All it takes is a few seconds at full throttle.

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Jim,


I think you might be wrong... A grease packed, sealed bearing will remain that way...

It is designed to keep the grease in it and the contact seals actually prevent it from leaving and keep dirt; both liquid and solid, from coming in...

What is the point of sealing the bearing otherwise?


Only a damaged seal will cause the bearing to puke its grease.

RE: about bearings
 

I have seen enough of the "sealed" rear bearings in OS four strokes that are gritty or dry that I'm sure they leak and are eventually flushed out or contaminated. The front bearing has a much easier life. Seals are not that tight. They are not meant to hold pressure, mainly to keep dust and dirt out. One has to be specific about the type of seal. There are contact and non-contact types. Contact seals are draggy. I've never seen a "double sealed" bearing to imply anything other than having seals on both sides.

RE: about bearings
 

Quote:

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ORIGINAL: gkamysz

I've never seen a "double sealed" bearing to imply anything other than having seals on both sides.

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Greg,


True, this is ALL it means.

I never meant to imply anything else...


As to seals being draggy... They are drenched in grease and although it is perceptible, the friction is not that great.

Some better contact sealed bearings employ a Teflon lip, to decrease the friction even more.


A sealed rear bearing can be a problem, since it prevents lubrication from reaching the front rotary valve area...

The seal there would be lesser and even wear can result.

RE: about bearings
 

Dar, please note that I said OS four strokes. I don't think a two stroke would suffer from a sealed rear bearing very much. The fuel does come through the intake after all. Liquid_TR mentioned the 160FX is supplied with a sealed rear bearing.

RE: about bearings
 

I get the grins every time I see this discussion, I have several engines where there is no seal on the front of the front bearing, Fox, OPS etc. I have never seen anything but a very shiny new looking front bearing when pulling the prop driver regardles of the engines age or amount of use.

RE: about bearings
 

We should distinguish between sealed and shielded bearings. All of the front bearings I've bought recently have had those thin metal shields on both sides. I pop off the rear shield and leave the front one in place. I haven't purchased any sealed bearings that I can remember.

David

RE: about bearings
 

David,


There are several different opinions...

Most OS .40-.55 engines come with a shielded bearing in front...

The (originally) clone Thunder Tiger Pro comes with a single sealed front bearing.


But as to replacement bearings; if the front bearing came grease-packed and sealed on both sides, I see no reason to remove the inner seal...

Or does anyone here see justification to remove it and to give up the grease packing?

RE: about bearings
 

Dave, try that on one of your Saito's! I put a shielded bearing into the nose of my FA-80 by mistake, and man is that a leaker!

RE: about bearings
 

I guess if the engine's original front bearing was sealed I would replace it with another sealed one. But, so far I don't own any engines that came with sealed front bearings.

The only engine I own that leaks out the front is my OS Max .50. It has a needle (roller) bearing in the front. It may be that this type of bearing is simply more prone to leaking by design.

David

RE: about bearings
 

Oops sorry if i didnt make it clear, i didnt say they are supplied with sealed bearings. Original 160FX rear bearings are open type NSK bearings.

I recently changed 2 sets and I bought sealed type one. But after seeing how much drag they add, i removed the seals and installed the new bearings into the engines.

also on another note, the rear sealed bearing in my OS 56FSa is still in prinstine shape.

If you think your sealed bearing is somehow puked its grease or got contaminated, im definite its seals are damaged in some way.

you can get the seals off of a bearing, remove the grease, check for any damage or roughness, clean with solvent.

if everything is ok, you can repack them with bearing grease (widely available in petrol stations) and put the seals back on - voila. fresh new bearing.

RE: about bearings
 

I was pretty sure while browsing Tower I saw that the 160FX used a sealed bearing.

I've seen the problems with both OS and Saito four strokes with sealed bearings.

RE: about bearings
 

When I've pulled the seals from "sealed" bearings that have been installed in model engines for any length of time there's usually no sign of grease left in them.

The seals are designed to keep a relatively thick grease in but what I think happens is that the much thinner oil in our engines is forced into the bearings over time where it dilutes and utlimately washes that grease out.

Remember that unless you're talking about a labyrinth seal (which isn't what's used on these bearings) there's also the fact that there will be contact between the seal and the rotating inner. Eventually (especially at 15K RPMs) wear will occur and the seal will no longer remain intact - at which time oil will find it easier to enter and flush out the grease.

RE: about bearings
 

Hello, Two important factors relating to bearings, are RPM's and temperature. Bearing manufacturers recommend oil lubrication for high RPM and high temps.
Oil is more capable at carrying away heat and remaining in contact with the balls for lubrication. Grease can be (at temperature) flung away, past shields and seals. Oil in the incoming air/fuel charge would have to fight it's way through the seal to the balls. I think, fit bearings,seals as per engine manufacturers instructions. I repair various machinery on a daily basis and anything that runs at speed is generally oil lubricated.

RE: about bearings
 

You are correct and I think most manufacturers rate their open bearings to higher RPMs than their sealed units.

In our applications, the front bearing (and I'm only taking about the front bearing since very few model engines use sealed rear races) are still operating at very conservative RPMs (compared to the manufacturer's ratings) and also at comparatively low temperatures (due to the cooling effect of the intake charge in the crankshaft in the case of shaft-induction 2-strokes).

In all the bearing changes I've done over the years (on my own and other people's engines) I've only ever encountered *one* front bearing that could not have been re-used if you felt like it - and that was because of massive corrosion). Generally speaking, the front bearing gets a pretty easy life and wears/corrodes at a far lower rate than the rear one - whether sealed or not.

It's interesting to note that there are a growing number of engines that come from the factory with sealed front bearings.

RE: about bearings
 

I'm in complete agreement with you TR. If you worry about real contaminants run with an air filter.

Bill

RE: about bearings
 

Agreed.

Bill

RE: about bearings
 

Yep, save the grease for your auto and trailer wheel bearings, they don't turn 14,000 RPM. Ball, roller and needle bearings require very little lubrication and are manufactured with such percision they require no break-in. Your piston, rings and cylinder are the lubrication hogs.

Bill