Ram Jet

Right Dar, a shielded bearing my lose grease, a sealed bearing should not.

Bill

Ram Jet

I don't think I've ever seen a sealed needle bearing. That doesn't mean there isn't any. I can see where a needle bearing would leak. On motorcycles you usually will only find a needle bearing on the small end of the con rod. If a needle bearing is exposed to the outside elements it will have a proper neoprene seal protecting it. That is the case with the old Mercury Hurricane outboad 20 C.I. engines which run needle bearings as crankshaft main bearings.

Bill

Ram Jet

Just a suggestion. If you do clean ball or roller bearings and blow them out with compressed air please resist the temptaton to spin the bearings with the compressed air. It's loads of fun fur you, hell for dry bearings.

Bill

Ram Jet

I agree. On a two cycle I think an outer SEAL not SHIELD is mandatory to avoid crankcase gas leakage and on a four cycle - a smart thing to do. No inner seals or shields.

Bill

DarZeelon

Quote:

ORIGINAL: Ram Jet

...On a two-stroke engine, I think an outer SEAL not SHIELD is mandatory to avoid crankcase gas leakage and on a four cycle - a smart thing to do.
No inner seals or shields.

Bill,


You are new here, so I will have to repeat myself once again.

1. In a two-stroke engine it is not the bearing's job to seal the engine... It is the job of the crankshaft and the front crankcase, in the front rotary valve.
If your engine leaks profusely from the front, a sealed bearing will lessen that 'runny nose syndrome' (or non-stop idling...). But this is just Aspirin to a cancer patient...

Many good engines, like those from Fox and Webra, use an open front bearing, yet produce no noticeable leakage.

2. Your second idea is contradicted by the pros... Bearing outlets tell you to leave the inner seal of your new, grease-packed, double-sealed front bearing in place.

The bearing grease contained within this front bearing, is a much better lubricant than methanol diluted oil-spray, so there's no point in removing the inner seal.

With the grease and both seals in place, this bearing will outlast your engine...


If the bearing has two steel shields, however, it is recommended that the inner one is removed, so as not to interfere with bearing lubrication.

RC-Bearings

My Feedback: (1)

Oh well. Getting in on this one a little late, but here are my thoughts on this subject.

Dar is essentially correct in everything he said. Sealed bearings are used on a lot of engines for a reason. There are two main reasons: 1) There is no lubricant available from the lower end of the engine (YS four strokes, etc), or 2) The engine manufacturer is not able to machine the front of the engine with enough sealing area to prevent excess leakage from the front (Saito, etc). Neither one of these reasons are because of bad manufacturing or design. They are just that way.

A good sealed bearing with the proper grease should outlast the engine. Contrary to some statements here, if the engine is in good operating condition, oil should not get past the seals or flush out the grease.

The inner shield does not need to be removed on a double shielded bearing for oil to get to the inside. The gap between the inner race and the shield is larger than the gap between the crankcase and shaft. Any oil that gets past the case/crank gap will easily get to the bearing. Where else can it go?

Hobbsy

My Feedback: (102)

There are several brands of engines that have no seal on the front of the front bearing, I have never seen one of these bearings dirty or anything but shiny and clean.

Jetdesign

My Feedback: (8)

Hi, I'm new at this and have some questions:
I had a rear (shielded on one side) bearing go bad on an OS engine. I was told by some talented and experienced pilots to replace it with a sealed, stainless bearing packed with grease. This was contrary to the original bearing and the advice of Boca bearings. Upon installing the sealed rear bearing (using an oven preheated at 250* for 10 minutes) the new bearing began to leak grease, which had thinned out due to the (low) temperature.

Is there something wrong with that bearing? Why did it leak? If it can leak warm grease, can't engine oil get inside and lube the bearing?

I agree that the sealed bearing feels more 'draggy' than the shielded bearing; maybe this changes with heat?

Can the seals of that bearing be removed, bearing cleaned and lubed, and used as an open bearing?

The front bearing is shielded; I believe on both sides but I can't remember now.

I ended up having the engine replaced due to another issue. It has a new, shielded-on-one-side bearing in the rear, and I still have the partially leaked stainless sealed bearing. I will use the bearing that came in the engine until there is a problem; what should I do if/when it goes bad?

DarZeelon

Quote:

ORIGINAL: gaRCfield

I had a rear (shielded on one side) bearing go bad on an OS engine.

Garfield,


This is not news!

For some reason, it seems most of those who experience bad bearings, have them in OS engines...

I do not know if OS source 'junk bearings', or if their engine assembly process overloads the bearings, causing them to fail prematurely (I have seen a new OS1.40RX 'puke' its rear bearing the first time ever it was run...)...[:@]

...Or is it because of user error, fuel, behavior, Etc.?[sm=bananahead.gif]

I have an MVVS .49, with about 120 hours on its original bearings.

Quote:

I was told by some talented and experienced pilots to replace it with a sealed, stainless bearing packed with grease. This was contrary to the original bearing and the advice of Boca bearings. Upon installing the sealed rear bearing (using an oven preheated at 250* for 10 minutes) the new bearing began to leak grease, which had thinned out due to the (low) temperature.

Is there something wrong with that bearing? Why did it leak? If it can leak warm grease, can't engine oil get inside and lube the bearing?

I agree that the sealed bearing feels more 'draggy' than the shielded bearing; maybe this changes with heat?

Can the seals of that bearing be removed, bearing cleaned and lubed, and used as an open bearing?

A sealed rear bearing should only be used if there is a source for lubrication for the crankshaft's large journal (which DOES contact the surrounding crankcase, while sealing against it, in the front rotary valve area...) and the front bearing (unless it also is sealed and grease-packed).

Otherwise, this would be wrong advice.

Any sealed bearing can be made into an open bearing, but the grease contained within it may not be methanol soluble... You will have to thoroughly wash it out (making sure no contaminants are inadvertently shoved into it...

jaka

Hi!
If you want your engine to give max power and perform ...get rid of any thing that can produce friction (grease , rubber seals, and metal shields) and use C3 or C4 bearing of good quality like those Swiss WIB bearings with plastic retainers that MVVS, Nelson and JET use in their engines.
Here is a 28x15x7 mm rear bearing (like as most .40-.46 engines use) that is taken from a ASP .40 /Kyosho GX.40 that has been run on a British manufacturers all synthetic fuel containing no rust inhibitor.

A new WIB 28x15x7mm, C4 bearing to the left.

chistech

As far as drag on a sealed greased bearing, the drag will virtually go away once the bearing has heated up to operating temperature. When turning the bearing by hand when cold, it will feel not as free as a non greased bearing. As far as high speed bearings using oil and not grease, there are certain rules. If you have ever changed rear axle bearings on a live axle type pickup or truck you have to grease the tapered roller bearings even though they are lubricated by the oil in the rear. If you don't grease them they will sieze up before the oil can get to them, and applying axle oil will not guaranty they won't either. So, if you put a sealed bearing in your motor and the grease get worked out eventually thru use and is replaced with a mixture of oil and fuel, it is better than starting up the motor with a dry bearing. I will oil my bearings with synthetic oil when installing new. I actually heat the motor first with my HD heatgun to help simulate running temps. Heat helps pull the oil into the crevases. I might not have to do it but it's just my habits. I have been a millright and machinery mechanic for over 25 years and was taught a lot of things by the "old school" guys.

Gungadin

Anyone know of a Stateside source for WIB Swiss bearings ?

w8ye

My Feedback: (16)

Mike Cathey at [email protected] $40+S&H

gkamysz

My Feedback: (19)

Do you have a manufacturer's reference for this? I have to think that NSK talked to OS about the application of their bearings. The NSK bearings supplied in OS four strokes are of their "V" seal variety. This type of seal is a non contact rubber seal. It will not keep grease in, or oil out, when used in a model engine.

Ram Jet

Yes and maybe not under any significant pressure.[sm=50_50.gif]

Bill

ace4-40

They won't. If you squirt oil into the breather it will come out the front bearing. And NSK aren't cheap bearings. Mine last for years. The only failures I've had are from rust and that's MY fault.

DarZeelon

Greg,


Sealed bearings should, under their normal operating environment, keep the grease in and the oil/air out.

This is what they are designed to do.

Pressures inside an engine's crankcase never exceed 2 bar and are mostly much lower than that; varying rapidly from a partial vacuum to low, over-atmospheric pressure.


If sealed bearings are not designed to seal than why does a prominent model engine bearing supplier sell sealed front bearings, as a 'remedy' for engines that suffer from the 'runny nose syndrome'?
Had these bearings not sealed, the engine's nose would remain runny, don't you think?


The NSK bearings you are referring to in OS engines... are they really sealed??? It seems they have flexible 'shields', to keep large pieces of grit out, or are simply dysfunctional, or maybe their seals are made of a material that deteriorates and fails, when run in a methanol environment, causing the bearing to puke its grease...


The model engine industry is small... So small in fact, that some suppliers make substandard products for it; yet don't care enough to redesign those that fail.


The 'bozo' modeler will just shell out the cash and replace it anyway, so it can fail once again...[:@][:'(]


A sealed bearing must be sealed. Period.

Ram Jet

Good points Dar. It seems to me that the bearing seal could easily contain the positive and negative pressure pulses created in a two cycle engine's crankcase. I don't think we are dealing with pressures anything like 10 p.s.i. The seal materials ability to function properly in a methanol environment is not something I had given any thought to.

Bill

DarZeelon

Quote:

ORIGINAL: Ram Jet

...The seal materials ability to function properly in a methanol environment is not something I had given any thought to.

You are not the only one who missed that point, Bill...


Some larger glow engine producers failed on that point, when they utilized Walbro carburettors, on glow-fueled engines...

The diaphragms deteriorate over time. This also goes for some fuel-pump/regulator makers, who use the same diaphragms...


The seals installed in most bearings are insusceptible to petroleum based grease, oils and also fuel...

But methanol/ethanol/E85 required even that some components of automotive fuel-injection systems, to avert early failure...

gkamysz

My Feedback: (19)

Dar, are you guessing? Maybe you've read a bearing manufacturer's technical reference supporting what you said? NSK offers 3 types of "seals" The V type is a non contact rubber seal. That's what they call it. Then they have a "light contact", and a "contact seal". Which one will actually keep grease in and oil/solvents out? Zenoah G20 uses an NSK bearing on the nose and it appears to be the contact seal variety. There appears to be no separate shaft seal on the front shaft. The bearing manufacturers also have something to say about grease life in sealed bearings.

Ram Jet

You confirm what I read years ago. If you convert an automobile carb from gas to methanol vearious seals, O rings etc must be changed, and vice versa.

Thank you,
Bill

w8ye

My Feedback: (16)

A two stroke gasoline engine must have a positive seal for the crankcase or the combustion cycle will not work.

A two stroke gasoline engine will not draw fuel if a bearing gets hot and ruins the seal.

The pump in the carb doesn't work either

Ram Jet

Thanks w8. Lessons learned the hard way on a West Bend 580 go cart engine when I was 13 and a 20 C.I. Mercury outboard that had the crank seal surface eaten by wire worms in my dads damp basement. Your confirmation of the importance of two cycle crankcase sealing will help all RCU members. I extensively use Permatex High Tack gasket sealer on all mating surfaces of my engines as insurance - most of the time without a gasket.

Bill

DarZeelon

Quote:

ORIGINAL: gkamysz

Dar, are you guessing?

Greg,


Guessing? Nooooo!

A seal, by definition, should seal, or do you think otherwise?


If it leaks then what do you think it should be called ... a leak, perhaps???

gkamysz

My Feedback: (19)

If you were an engineer that would be a guess, not even a good one. If the supplier offers 3 types of "sealed" bearings the first question that should come to mind is: "What are the differences?" Telling your customer, "well the supplier said it was sealed" won't cut it. If you talked to the supplier and they said it meets your application and will provide "xx" hours of service, then you have covered your tail, and you'd better review the application if it fails. If you looked it up in the manufacturers technical reference, but didn't bother checking with them, that would have been a good guess depending on prior experience with similar applications. If you just picked it out of the catalog and put it into your prototypes and did the tests yourself to prove the performance, that would be OK if you covered all of the possible situations it might experience. There are many ways to go about specifying a parts for an application, but assuming because a word was used in the description is not the best way to do something. Seals have varying degrees of performance, depending on design, application, and how much added friction the mechanism can tolerate.

Maybe you missed the fact that the seals in OS fours stroke are NSK's non contact variety. If there is no contact, how good of a seal is there?. And if the seal doesn't really seal well, how can one assume that grease will stay in and fuel/oil will stay out?

Somebody posted that YS four strokes don't have oil in the crankcase. This is not true. A disk valve which is used to time the flow of air through the crankcase for supercharging would not last long without oil. Oil gets there just like any other four stroke, due to leakage past the piston ring.